JBED
Journal of Building Enclosure Design
An official publication of the Building Enclosure Technology and Environment
Council (BETEC) of the National Institute of Building Sciences (NIBS)
Summer 2006
Comfort and Productivity:
The Fenestration Factor
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Contents
10
Dynamic, Integrated Façade
Systems for Energy Efficiency
and Comfort
Published For:
NIBS / BETEC
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All That Glass?
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32
37
Occupant Thermal Comfort
and Curtain Wall Selection
Architectural Glazing for Sound
Isolation (an Acoustician’s
Perspective)
Window Comfort & Energy
Codes
PRESIDENT & CEO
Jack Andress
PUBLISHER
Maurice P. LaBorde
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Shannon Lutter
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EDITOR
Jon Waldman
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ADMINISTRATION
Shoshana Weinberg, Pat Andress
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ADVERTISING DESIGN
James Robinson
LAYOUT & DESIGN
J. Peters
2006 Matrix Group Publishing. All rights
reserved. Contents may not be reproduced by
any means, in whole or in part, without the
prior written permission of the publisher. The
opinions expressed in JBED are not necessarily
those of Matrix Group Publishing.
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39
Security 41
39
Messages:
06
08
From NIBS President, David A. Harris
Thermal
Comfort
Laminated Glass, Providing
Security against Terrorist Attacks
How Does Fenestration Fit In?
Fenestration
Questions
JBED
Features:
41
From BETEC Chairman, Wagdy Anis
Industry Updates:
45
46
47
50
Tax Credits Made Easy by Choosing
ENERGY STAR®
NFRC Standards, Codes and Fenestration
Research Activities
BEC Corner
Buyer’s Guide
On the cover: The glassenclosed von der Heyden
pavilion at the Perkins Library,
renovated and expanded by
Shepley Bulfinch Richardson and
Abbott at Duke University,
creates transparency by
connecting the interior with
nature and outdoor campus
activity.
Photo by: Albert Vecerka/ESTO.
Summer 2006 5
Message from NIBS
David A. Harris, FAIA
With mold and
other moisturerelated problems
perpetuating,
energy efficiency
becoming more
critical with
escalating energy
costs, and design
professionals and
constructors in
need of reliable
guidance, JBED
will fill a critical
void.
WELCOME TO THE JOURNAL OF Building Enclosure Design (JBED)! The National
Institute of Building Sciences and its Building Enclosure Technology and Environment Council (BETEC) is pleased to team with Matrix Group Publishing to produce this inaugural issue of the Journal of Building Enclosure Design. This new and
important magazine will become an essential information source on research and
development issues related to building enclosure systems for North America.
With mold and other moisture-related problems perpetuating, energy efficiency becoming more critical with escalating energy costs and design professionals and constructors in need of reliable guidance, JBED will fill a critical void.
Through the multi-disciplinary professional members of BETEC and Matrix’s
publishing capabilities, facility professionals across North America will have a new
and reliable source of information through which to improve the performance of
exterior walls, below-grade, roof and fenestration systems and the related impacts on indoor environments.
NIBS’ and BETEC’s past contributions are featured content of the Whole
Building Design Guide (www.wbdg.org). They include the results of numerous research initiatives and symposia, the Envelope Design Guide and form a substantial
portion of the basis for technical and editorial content of our biannual journal. By
distributing it widely to members of NIBS councils, corporate, government and
association personnel, design and construction professionals, and researchers and
academics throughout Canada and the United States, the value of BETEC’s contributions will be greatly expanded.
In addition to BETEC’s focus on building enclosure issues, NIBS and its other
councils have, for nearly 30 years, addressed the broad range of facility-related
issues through hundreds of multi-disciplinary and cooperative initiatives. They include health, safety, security, health care and educational facilities, natural and environmental hazard assessment and mitigation, information technology, standards
and criteria development, facility life-cycle needs, life-lines research and information dissemination to name a few. Please visit NIBS website at www.nibs.org. We
encourage your use of our products and seek your participation in our programs.
Together we can successfully improve the performance of the built environment.
We invite our readers to carefully review this inaugural issue and ask you to
let us know how you like it. Please provide critical feed back to Matrix Group
Publishing or NIBS so we can make this publication better and more responsive
to your needs.
David A. Harris, FAIA
President
National Institute of Building Sciences
For NIBS membership information, go to www.nibs.org.
WHAT IS NIBS?
NIBS is a non-profit, non-governmental organization bringing
together representatives of government, the professions, industry,
labor and consumer interests to focus on the identification and resolution of problems and potential problems that hamper the construction of safe, affordable structures for housing, commerce and
industry throughout the United States.
The Institute’s board of directors consists of 21 members. Six,
6 Journal of Building Enclosure Design
which represent the public interest, are appointed by the President
of the United States with the advice and consent of the U.S. Senate. The remaining 15 members are elected from the nation’s building community and include consumer and public interest representatives as well as representatives of industry. A majority of the
NIBS’ board represents public interest sectors as prescribed in the
authorizing legislation.
For more information visit www.nibs.org.
Message from BETEC
Wagdy Anis, AIA, LEED A-P
“The purpose of
the Councils is to
promote and
encourage
discussion, training,
education,
technology
transfer, the
exchange of
information about
local issues and
cases, relevant
weather conditions,
and all matters
concerning building
enclosures and the
related science.”
WELCOME TO JBED, THE JOURNAL of Building
Enclosure Design.
The Building Enclosure Technology and Environment Council (BETEC), one of the councils of
the National Institute of Building Sciences, along
with Matrix Group Publishing, is pleased to lead
the effort to publish the Journal of Building Enclosure
Design, JBED. This new publication will quickly become an essential vehicle for the dissemination of
information on research and development issues
related to building enclosure science and technology, in full alignment with BETEC’s mission.
With losses due to hurricane damage and other
natural disasters, mold affecting and triggering the
burgeoning asthma population, moisture accumulation determining the durability of enclosures and
shortening their useful service lives, fossil fuel energy sources becoming threatened and energy
costs escalating and the design and construction
community in need of useful information and guidance, JBED is offered to provide just that. The
United States represents all the climates of the
world and designing enclosures for each climate
and building use is a challenge this publication
plans to address.
One of BETEC’s important successes in the recent past is establishing the Building Enclosure
Councils or “BECs” in different cities of the US, in
partnership with the American Institute of Architects (AIA), following the successful precedent set
in Canada. As of this writing, 13 BECs are in place
in most of the climate zones, and at least 6 more
are planned.
I believe the BECs, as they mature, will help
bring building science of the building enclosure to
the mainstream. To contact the BEC’s, go to
www.bec-national.org/ boardchairs.html.
We will be bringing you news and events of the
BECs on a regular basis in this publication through
the “BEC Corner.”
Another recent success of BETEC is the
For BETEC membership
information, go to
www.nibs.org/betec
8 Journal of Building Enclosure Design
publishing of NIBS/ASHRAE Guideline 3: Commissioning the Building Enclosure. As of this writing, the
publication is available for public review free for a
limited time only, until July 21, 2006:
www.nibs.org/ GL3.html. For the first time, commissioning the building enclosure has been organized as a process, in conjunction with ASHRAE
/NIBS Guideline 0, The Commissioning Process. This
has been a substantial effort that lasted two years,
and your feedback would be very helpful.
The Building Enclosure Design Guide, a huge effort of over a thousand pages, is now published on
the web as part of the Whole Building Design
Guide, www.wbdg.org and will be featured in future editions of JBED.
This article will be a vehicle to bring you
BETEC news and its directions in the future.
BETEC membership is open to all organizations
and individuals having an interest in BETEC’s
goals. www.nibs.org/betecmem.html.
We hope you enjoy this edition of JBED. Please
send us your opinions and ideas regarding how to
improve it. The JBED Editorial Board solicits the
articles and submits them for peer review. It is important to make clear that in no way does NIBS or
BETEC control or review the content or claims
made by advertisers in JBED, nor is NIBS, BETEC
or Matrix Group Publishing responsible for the use
or application of any information provided in
JBED.
We look forward to hearing from you. Please
encourage anyone you know who may be interested in receiving a copy of JBED to e-mail
jbed@nibs.org.
Thank you,
Wagdy Anis, AIA, LEED A-P
Chairman, BETEC
Chairman, JBED Editorial Board
Principal, Shepley Bulfinch Richardson and Abbott
All of Alaska in
Zone 7 except for
the following Borroughs in Zone 8:
Bethel
Northwest Arctic
Dellingham
Southeast Fairbanks
Fairbanks N. Star
Wade Hampton
Nome
Yukon-Koyukak
North Slope
Zone 1 includes:
Hawaii
Guam
Puerto Rico
The Virgin Islands
Warm-humid below the
white line
Feature
Dynamic, Integrated Façade Systems
for Energy Efficiency and Comfort
By Stephen Selkowitz and Eleanor Lee,
Lawrence Berkeley National Laboratory
SUMMARY
In a world with growing concerns
about global energy use and carbon emissions, and with limited short-term options
for increasing renewable energy supplies,
highly energy efficient and sustainable
building design becomes a necessity.
Buildings use more than 1/3 of all U.S. energy and more than 2/3 of all electricity—
it is therefore difficult to change national
energy use and carbon emissions without
addressing energy use patterns in buildings.
Architects design buildings with highly
glazed façades in climates worldwide. It is
impossible to “optimize” building performance with static glazings alone since
sunlight/daylight intensity varies dramatically with location, orientation, climate
and time. Providing optimal energy efficiency for owners, and thermal and visual
comfort for occupants, requires dynamic,
interactive façade systems to actively control solar gain, daylight and glare. Successful solutions require proper technology
selection, integration between building
systems and optimized sensing and control strategies.
Although the concepts are well
known, these solutions are not commonly
available today as affordable, specifiable
and reliable packages. We describe recent
project results following several technology pathways that have made progress toward the goal of dynamic façade solutions.
Automated motorized blinds and shades,
integrated with a daylight responsive, dimmable lighting system can provide solutions today.
Working with the New York Times, a
full-scale mockup of part of a typical floor
of a 52-storey, all-glass building was constructed, and a variety of interior motorized roller shades and dimmable lighting
options were extensively simulated,
10 Journal of Building Enclosure Design
tested and optimized. Performance specifications were developed to guide competitive procurement and affordable new
systems were developed that will shortly
be installed and commissioned in the
building, for occupancy in 2007. Looking
forward, we also tested and simulated
electrochromic “smart glass” façade prototypes in three side-by-side full size test
rooms with integrated HVAC and lighting
systems. Energy and demand impacts of
alternate control strategies were also
measured and occupant responses were
also studied.
The control and integration results
from both projects demonstrate that dynamic façade technologies can provide desired energy performance levels, demand
response and load management, and also
reliably deliver visual and thermal comfort
in indoor workspaces.
INTRODUCTION AND BACKGROUND
The “oil shocks” of the 1970s awakened many people to the realization that
overall energy use in buildings could be
reduced with better design and improved
technology. In a nation where single glazing was the norm in most buildings, windows were commonly the thermally
worst element from a perspective of both
heat gain and loss. The regulatory response was typically to minimize window
area and to require thermally improved
technology, i.e. double glazing. The immediate crisis also stimulated a new look at
passive solar heating and daylighting, two
design approaches that attempt to capture benefits from window performance,
but neither approach reached mainstream
practice before energy availability and
prices stabilized and the design profession
returned to a largely “business-as-usual”
approach.
Thirty years later, new environmental
challenges have made their way to the
newspaper headlines and to the practice
of building design and operations. At any
given time, building designs reflect the influence of a wide range of issues and
trends. These include not only the technical constraints of available technologies
but also economic, cultural and business
trends and market drivers. Glass is recognized as a key element in the architectural
expression of the building, provides occupants with a visual connection to the outdoors and provides daylight indoors to enhance the quality of the interior work
environment. The building envelope
serves an important functional role to help
maintain proper interior working environments under highly variable external environmental conditions. The primary technical challenges of envelope environmental
control include heating, cooling and lighting energy use and electric demand, and
the final design decisions impact not only
the owner who pays for the energy use
but society at large due to resource depletion, carbon emissions, and other related regional and global environmental impacts.
The conventional approach to façade
design in the U.S. has been for the architect and owner, to determine glazing
areas and orientation, leaving the engineering team to select a glazing solution
that provides some degree of damage
control using static thermal and solar control technology. The strategy then required provision of large (typically oversized) HVAC systems to provide thermal
comfort and provision of interior shading
to manage glare and provide visual comfort. When highly glazed façades have
been specified in the past the glass selection was normally heat absorbing and/or
reflective, thus providing some control of
radiant gain but at the expense of daylight.
Prior to the 1980s, most glazing was single
glazed, and although double glazing is now
the dominant glazing choice, many designs
still use thermally unbroken metal framing, resulting in relatively high conductive/convective loads that are neutralized
by powerful HVAC systems at the building
perimeter. These peak perimeter zone
heating and cooling loads are often the
major factor in sizing building HVAC systems, adding significant cost to the building. Properly operated shades and blinds
might reduce loads, but no engineer
would trust that manual operation would
consistently provide sufficient control to
“rightsize” chillers and HVAC distribution
systems.
A variety of business, market and technical forces have conspired to change design practice over the last 20 years. Building energy codes and standards have been
tightened, reflecting a growing societal interest in energy efficient, sustainable designs. Owners have shown a renewed interest in providing more comfortable and
productive work environments in the context of “green buildings”. Glass and façade
manufacturers now offer a wider range of
affordable double glazing system solutions
that provide better thermal and solar control without sacrificing daylight e.g. spectrally selective low-E glazings.
These advances came at a fortuitous
time because the growing interest in highly glazed façades makes new demands on
designers and manufacturers. The new
challenge is to provide a fully functional
and integrated façade and lighting system
that operates appropriately under a wide
range of environmental conditions and addresses the full breadth of occupant subjective desires as well as objective performance requirements. These rigorous
performance goals must be achieved with
solutions that are initially affordable and
cost effective and then must operate over
long periods with minimal maintenance if
they are to be accepted and purchased by
building owners. The current high level of
uncertainly and risk, both real and perceived, must be reduced by generating
objective performance data that demonstrates the viability of these solutions.
In prior studies we used extensive
computer simulation studies to analyze
and optimize the designs of high performance façades. In this paper we describe
recent results from two field tests of
integrated, high performance façade systems that, in partnership with manufacturers and building owners, are contributing
toward reaching these challenging performance goals.
simultaneously controlling sunlight admittance while admitting adequate daylight to
offset electric lighting needs. These control issues are shown schematically in Figure 1 below. In the remainder of this
paper we focus on the sunlight/daylight
control optimization issue.
PERFORMANCE REQUIREMENTS IN
HIGHLY GLAZED BUILDINGS
If all owner, occupant and society performance needs must be
met with high performance
façades, glazing systems alone will
be inadequate. Glass selection
might provide good performance
where glazing area is judiciously
limited on an orientation basis in
climates that are not severe, but if
one chooses to use large glazed
Figure 1
areas on most orientations in a
Schematic of control logic to manage dynamic window system and dimmable
wide range of climates then new
lighting. A smart controller must be capable of responding effectively to a wide
range of input conditions, shown on the left.
performance capabilities must be
added to even the best of today’s
glazing technology.
THE CHALLENGE OF DYNAMIC CONTROL OF
Thermal losses in winter can be adSOLAR GAIN AND DAYLIGHT IN ADVANCED
dressed by specifying highly insulated glazFAÇADES
ings. A standard, U.S. glazing today is a
We explored two pathways for develdouble glazed unit with low-E coating and
oping high performance façades that are
gas fill, attaining a center glass U-value of
fully integrated with automated dimmable
about 1.4 to 1.6 W/m2-C in typical conlighting systems, and are responsive to
changing owner and occupant needs. We
structions. Even lower conductance levels
first examined technology that is widely
may be needed, not so much as an energy
available, although not commonly used,
saving strategy but to minimize thermal
automated shades and blinds, to provide
discomfort and condensation. Furtherdynamic control of solar gain, daylight and
more the overall conductance of the comglare. We then looked to the future and
plete façade system is typically worse than
examined the use of emerging “smart
the glazing alone since it includes the
glazings”, specifically electrochromic glazmetal framing elements and glass edge
ings. In both cases, integrated daylight
conditions, so overall façade conductance
dimming controls are essential to reduce
can be 10 per cent to 40 per cent higher
lighting energy use, and in both cases conthan the glass conductance, depending
trol strategies that address occupant
upon framing details and glass areas. The
needs for comfort and performance are
National Fenestration Rating Council
balanced against building owner needs to
(NFRC) has developed standardized, acminimize building operating costs. While
curate methods to rate the performance
extensive parametric computer simulation
of complete window and façade systems.
of façade and building performance is a
Highly insulating glazings still require
critical element of these studies, computadditional development but the bigger
er modeling alone is insufficient to address
challenge is dynamic control of sunlight to
issues such as glare and subjective remodulate solar gain, daylight, view and
sponse to the indoor environment, and to
glare. There are two fundamental issues
understand and solve problems in a manto address in control of sunlight: 1) the
ner that leads to change in the marketmechanism(s) to physically control intensiplace. Therefore, each of these research
ty e.g. absorption, reflection; and 2) the
efforts relied on field tests and each incontrol logic by which the change in
cludes studies of human factor issues as
transmittance is triggered and activated.
well as engineering optimization.
Finally one should note the challenge of
Summer 2006 11
1. COMMERCIALLY AVAILABLE
SOLUTIONS: AUTOMATED BLINDS
AND SHADES
Blinds and shades are used in most
U.S. buildings today but unlike European
experience, virtually none are motorized
and few are externally mounted. The assumption is that that these shading systems are available for occupants to control localized glare and solar gain but they
are not relied on to control building envelope performance. Accordingly, most energy standards do not provide any credits
for systems that rely on occupant action
since the response is unknown and uncertain. Furthermore, engineers will generally
size HVAC systems assuming worst case
operating procedures—e.g. that the shading systems are not operated as planned.
Large glazed areas, even if heavily tinted
and reflective, may be insufficient to fully
control glare on sunny days.
the U.S., nor are systems that further link
the blinds to dimmable lighting controls.
Beginning with “off the shelf” blind and
lighting components, we developed and
tested an integrated, automated blind and
daylighting system in two identical sideby-side test rooms in a southeast facing
office building in Oakland, CA (Figures 2.1
and 2.2). Large cooling and lighting energy
savings were achieved, peak electrical savings were measured and the resultant automated systems were acceptable to occupants in a limited occupancy study.
Despite the success of the demonstration,
the lack of a cost-effective delivery system
managed by a single vendor or groups of
vendors continues to limit use of such systems.
The project illustrated the market obstacles from a building owner and manufacturer perspective in terms of who
serves the “systems integrator” role when
shades to highly transmissive veiling
fabrics. Although mechanically simpler
than blinds, once the fabric is chosen the
shade systems have more limited optical
control than blinds, largely based on their
position between up and down. It is possible to layer blinds or use optically variable
fabrics but this is not common practice.
An extensive field test program was conducted using an automated shade system
in conjunction with a high transmittance,
all glass façade for the New York Times
headquarters building, now under construction in New York City. The 52-storey,
140,000 m2 building will utilize fixed exterior shading and fritted glass in some loca-
Figures 2.1 and 2.2
Smart controls on the automated blind systems (left photo) keep direct sun out of the space, reducing glare and cooling loads. The same hardware system with different control strategies (right photo) admits sunlight to offset heating loads but creates excessive glare.
AUTOMATED VENETIAN BLIND AND
INTEGRATED DAYLIGHTING SYSTEMS
Venetian blind systems are widely
specified for control of solar gain and
glare. Because both the optical properties
of the slats and their tilt can be controlled,
they provide a wide range of optical and
solar control. But a number of field studies have shown that manually operated
blinds are rarely controlled in an optimal
manner. Adding sensors and controls and
automating the blind operation should
permit better control of both energy use
and comfort, assuming that the proper
control strategies can be successfully developed, implemented and maintained.
These integrated, automated control
systems are not yet commonly available in
12 Journal of Building Enclosure Design
the different system elements are provided from different vendors. Development
of smart, automated blind systems is
more advanced in Europe and Japan. Although a growing number of these systems are now being installed in buildings it
is still difficult to find measured performance data that clearly demonstrates the
overall energy use of such systems.
AUTOMATED MOTORIZED SHADE SYSTEMS
AND INTEGRATED DAYLIGHTING CONTROLS:
NEW YORK TIMES BUILDING
A second widely used operable shading system is based on roller shades.
Roller shade systems can utilize different
fabrics encompassing a wide range of solar
optical properties, ranging from blackout
tions (Figure 3.1) but will require interior
shades for sun control and glare control
and for thermal and visual comfort as well
as energy management.
The exterior of the building utilizes a
transparent floor-to-ceiling, all-glass
façade that encourages openness and
communication with the external world,
consistent with the owner’s dedication to
creating a high quality work environment
for their employees. Low partitions were
used to reinforce the sense of openness
and to let the daylight penetrate deeper
into the space. The cruciform floor plan
(Figure 3.2), with distances from interior
offices to façade of less than 7.6 m, permits view in three directions from most
Figures 3.1 and 3.2
Left (page 12): Exterior view of an all-glass façade and
shading system. Above: cruciform floor plan showing enclosed offices located toward the core.
locations within the perimeter zone. With
a generous ceiling height, a window-toexterior-wall ratio of 0.76 and a glazing
transmittance of Tv=0.75, daylight was
anticipated to be abundant throughout the
entire perimeter zone even with the exterior fixed shading system.
Overall solar heat gain would be a concern in any highly glazed façade. In this design, it is controlled with spectrally selective glazing (the glass solar heat gain
coefficient is 0.39 and the U-factor is 1.53
W/m2-°K) and with an array of exterior
fixed ceramic rods designed to block and
diffuse some sunlight as shown above.
Even with these systems, the owner understood that the transparency of the
façade would generate potential glare and
visibility problems for employees using
computers, so the owner wanted to explore the use of automated roller shades
as a means of managing window glare. As
well, conventional manually operated interior shades may have degraded many of
the key design features that made the architectural design so compelling in the
first place.
The building owner had sufficient foresight to begin addressing these critical
lighting quality and façade issues early
enough in the design process while there
was still time to explore potential dynamic
shading options and to evaluate and
Summer 2006 13
procure them for the final building. A survey of the marketplace by the design
team did not locate any vendors with
suitable products that fully addressed the
thermal and luminous issues in an affordable, integrated, and reliable package.
While dimmable lighting and motorized
shades have long been used as niche market products in corporate boardrooms,
the challenge for the owner was to push
the marketplace to respond with solutions with new, improved functionality,
suitable for an entire building but at lower
cost.
Based on LBNL’s prior research and
field testing, a partnership was created
between The New York Times, its design
team and LBNL to address this problem.
A full-scale 401 m 2 daylighting mockup
was constructed near the building site and
a number of vendors were invited to install their existing shading and daylighting
equipment. The mockup was extensively
monitored by LBNL in partnership with
the vendors over an 18-month field test,
with support from the New York State
Energy and Research and Development
lighting controls. A further objective of
the public agencies supporting the research was to help broaden the market
interest in these systems and design approaches with visits to the mockup from
other design firms and owners.
The fully furnished, full scale mockup
reproduced the southwest corner of a
typical floor (Figures 4.1 and 4.2). The
mockup was divided into two test areas.
Two different shade manufacturers and
two different manufacturers of dimmable
lighting systems installed systems in each
area with different types of sensors and
control strategies. The objective of the
test was not to perform a side-by-side
comparison of the two “competing” systems but rather to understand how vendor decisions regarding control infrastructure and design might impact actual field
operation. The end goal of the monitoring
phase was therefore not the selection of
one or another of the manufacturers’
products in the mockup but the development of a performance specification that
would be open for bid by any vendor.
Over 100 engineering parameters
Figures 4.1 and 4.2
Photograph of mockup interior (left) and RADIANCE nighttime rendering of the same space
(right). RADIANCE simulations were used to explore shading and lighting issues for conditions that
could not be tested in the mockup.
Authority (NYSERDA).
FAÇADE PERFORMANCE RESULTS FROM THE
NEW YORK TIMES DAYLIGHTING MOCKUP
The project was structured around the
availability of this unique full scale mockup. The New York Times mockup test
program was designed to: 1) enable vendors to demonstrate features of their systems; 2) fine tune their systems to meet
the evolving requirements of the building
owner; and 3) understand the benefits
and limitations of each manufacturer’s approach to shade management and day14 Journal of Building Enclosure Design
were measured continuously (1x/min,
24/7) in the mockup, including lighting energy use, work plane illuminance and distribution, various parameters related to
visual comfort, control operations, exterior solar conditions, and other environmental parameters. Monitored data was
collected over 9 months from December
21 to September 21 to capture the full
range of solar conditions. During this
time, the manufacturers were permitted
to tune their systems to obtain optimal
performance and improve their designs.
The building owner, upon seeing the effect of their initial control specifications,
tweaked some control settings to obtain a
system that better met their needs. In
some cases, manufacturers altered their
systems in response to interim performance data from LBNL when it was
demonstrated that the owner’s specifications were not being met.
At the end of the monitoring period,
The New York Times incorporated what
they learned into an open procurement
specification. Procurement specifications
for the lighting controls and for automated
shading systems were let out to all eligible
manufacturers for competitive bidding.
The winning vendors were then invited in
a further partnership with The New York
Times and LBNL to demonstrate performance capabilities of their final systems
in the daylighting mockup prior to installation in the headquarters building. The intent of this approach was to reduce risk
and uncertainty in all aspects of the procurement process, leading to assured performance at lower costs, and motivating
manufacturers to extend their product offerings.
More detailed analysis of technical results is available on the
LBNL website (see references). Initial testing
demonstrated that the
window and automated shade system provided useful daylight
throughout the 13.4 m
deep perimeter zone,
enabling significant
dimming of the electric
lighting throughout
much of the zone. For
this building design,
with its all-glass façade and minimal interior obstructions, even on the northwest
side the daily lighting energy savings were
20-40 per cent at 3.4 m from the window
over the nine-month monitored period in
Area A. The shading systems were controlled to provide a bright interior environment and control window glare. Lighting energy savings were substantially
greater in zones daylit bilaterally from
both the south and west façades in Area
B. In this area of the mockup savings averaged from 50-80 per cent at 3 m from the
façade and still achieved an average of 40
per cent at 6 m.
These daylighting savings were
achieved with a shading control strategy
that consistently blocked direct sunlight
and adverse sky glare but also reduced interior daylight levels, lighting energy savings, and access to view. The fabrics under
consideration in the roller shade systems
had an openness factor of three per cent
with an associated visible transmittance of
about six per cent.
To extend the test results, extensive
simulation studies of the impact of different shade control strategies were conducted. A prototypical virtual floor was
constructed for use with the Radiance
daylighting simulation model. The occupants’ view conditions and glare at 22 different task locations on each floor were
calculated for a lower floor (floor 6) with
extensive external obstructions, and for
floor 26 with largely unobstructed views.
This modeling confirmed that specific
shade fabric choices and control strategies
would influence the magnitude of energy
savings and likelihood of experiencing
glare conditions.
Controlled occupant studies were not
conducted but over 200 Times employees
had a chance to spend time in the mockup. The owner’s employees clearly preferred the brighter daylit space compared
to the darker, less daylighted spaces that
most currently occupy. They found the
quality of daylight to be palpably different
in the morning versus the afternoon and
were delighted with the subtle shifts in
color, intensity, sparkle and mood
throughout the day.
Glare control and the competing desire for openness and daylight remains a
challenge. The mockup provided very
powerful testing capabilities, allowed extensive exploration of alternate control
strategies under a range of sun and sky
conditions. Based on both mockup test
results and extended simulations, in the
building the shading systems will be fully
automated to respond to direct sun and
window glare and thus be responsive at
each task location to the specific requirements of the occupants and work groups,
window orientation, and degree of
Summer 2006 15
obstruction and/or daylight reflection
from the urban surroundings.
The automated shading and dimmable
lighting not only provide energy savings
but a demand response potential as well.
Studies are underway to determine how
to use the smart controls to bring the
building to a “low power” mode of operation that would allow essential building
functions to continue while substantially
reducing overall electric power use on a
hot summer day if the stability of the grid
was threatened. The automated shades
and dimmable lighting are a key element
in the demand response strategy. The final
step in this project will be to commission
the installed systems and verify that performance meets the design specifications.
Major construction will be completed in
2006 with occupancy in 2007.
2. THE ARCHITECTS’ HOLY GRAIL:
SMART GLAZING SYSTEMS
If the dynamic control of transmittance
was incorporated directly into glazing layers, some of the limitations of motorized
shades and blinds might be avoided. Researchers have been pursuing the quest
for switchable “smart glazings” for over
20 years and the laboratory accomplishments are now becoming available for initial purchase and use in buildings. As with
shades and blinds, the actual energy and
comfort performance in a building will depend on the interplay of the intrinsic
properties of the materials and the operating strategy of the building. These operating strategies must be developed not
only for energy and load control but to
meet occupant needs in terms of comfort
and productivity. As with the shade and
blind studies above, field studies in test
rooms and mockups are an important adjunct to the extensive computer modeling
studies that have already been completed
to quantify performance benefits and potential energy savings.
FIELD TESTS OF ELECTROCHROMIC “SMART
WINDOWS”
In 1999, the window systems in the
two test rooms in Oakland were retrofitted with a first generation electrochromic
window. The optical system changed from
a clear state with a transmittance of 51
per cent to a dark state transmission of 11
per cent. The system performed well
16 Journal of Building Enclosure Design
although full switching could take in excess of 15 minutes and the coatings had a
noticeable blue tint in the switched mode.
Detailed technical results are available on
our website.
In 2002 we constructed a new test facility at LBNL with three side-by-side test
rooms with unobstructed south views.
The entire glazed façade (3.5 m x 4 m) for
each room can be replaced. The lighting
power and the heating and cooling in each
room is individually monitored and the
rooms have a full array of illuminance and
luminance sensors for monitoring. Two of
the rooms were fitted with electrochromic samples over the complete
façade as shown in Figure 5. Since the
prototypes were of limited size the current façade requires 15 glazing panels.
Extensive engineering tests in the facility were conducted over a two-year period to explore the energy savings achieved
with different control strategies. We operated the electrochomics over their full dynamic range, testing different control
strategies designed to optimize lighting
savings, cooling savings and visual comfort.
We compared lighting and cooling loads
with automated electrochromics to results from the room with fixed glazing and
shading, with and without daylighting controls. The electrochromic systems were
able to consistently beat the energy use of
the conventional façade design but the de-
tailed results were highly dependent on
operating assumptions and specific control
strategies. The testing focused on the
challenge of the control optimization between glare control and daylighting energy
savings, with associated studies of cooling
impacts and peak demand impacts.
We also conducted human factor studies in this facility (Figure 6) to determine
desired operating and control parameters
of the glazing and lighting systems and to
better understand the issues associated
with smart glazing control strategies. Early
results suggest that the lowest transmittance level of the current glazing prototypes, three to four per cent, is usually adequate for most glare situations although
additional glare control was desired by
some occupants. However, switching the
entire façade to very low transmittance
levels to control glare often requires that
electric lights be turned to full power levels. New architectural design approaches
such as separate vision and daylighting
glazings, as well as improved switching
control strategies were then studied to
address this issue. Initial results show that
it is desirable to divide the façade into two
elements that would be designed and controlled differently. A lower “vision” window might have a lower transmittance
and would be designed to manage glare at
a perimeter workspace. This will tend to
have low transmittance values when sun
and sky glare are present so that LCD
screen visibility is not compromised. The
upper “daylighting” window would have a
higher visible transmittance and be managed dynamically to control solar gain but
admit adequate daylight so that the primary room electric lighting is off or
Figure 5
Exterior view of LBNL Façade Test Facility. Two rooms
at left have electrochromic prototypes installed, the room at
right is a control room with spectrally selective glass and
blinds.
Figure 6
Interior photo of façade test room configured for occupant
response testing.
provide active control of fenestration
transmittance and associated control of
electric lighting in building interiors are
now available and have been shown to be
capable of good performance and others
will emerge.
However it will take better and cheaper hardware, additional exploration of systems integration solutions, new sensors
and controls, improved commissioning, a
better understanding of occupant needs
and preferences, and better real time,
adaptive controls to fully realize the potentials of these emerging technologies.
Future building envelope design and operations will be increasingly integrated with
other building systems to achieve these
performance levels.
Figures 7.1 and 7.2
CCD photo of workstation (left) and false color luminance map (right) produced from image at left and 5 additional photos. Luminance map provides a dynamic
range of 5000:1
dimmed as much as possible. This approach adds to the design and control
complexity but delivers better amenity
and increased energy savings.
Better tools are needed to quantify the
visual environment in conjunction with
subjective and objective user studies in
these spaces. We have developed new
glare assessment approaches using CCD
images and processing of high dynamic
range image data to quantify, display and
understand these complex environmental
parameters that directly impact occupant
comfort, satisfaction and performance
(Figures 7.1 and 7.2). These techniques
can be used in the field to evaluate existing buildings as well as in a lab test environment.
REFERENCES
Extensive additional information on
these projects can be downloaded from
several LBNL websites:
• References for the New York Times
project can be found at: http://
windows.lbl.gov/comm_perf/newyorktimes.htm.
• References for the Electrochromics
project can be found at: http://windows. lbl.gov/comm_perf/electrochromic.
• A complete searchable list of LBNL
window and daylighting references,
from which current papers can be
downloaded can be found at:
http://windows.lbl.gov.
ACKNOWLEDGEMENTS
We acknowledge the active support of
numerous LBNL colleagues on the teams
that carried out the projects described
here, and the participation of other partners and consultants referenced at the
websites above. This work was supported
by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of
Building Technology, State and Community Programs, Office of Building Systems of
the U.S. Department of Energy under
Contract No. DE-AC03-76SF00098, by
the California Energy Commission, Public
Interest Energy Research Program, and by
the New York State Energy Research and
Development Authority.
■
CONCLUSIONS
A growing interest in daylighting and
sustainable design has led architects in the
direction of using highly glazed building
façades. Balancing the need for view, glare
control, thermal comfort with solar load
control and daylighting energy savings is a
complex challenge. In order for these designs to meet often contradictory performance objectives, they will need to
have a degree of active, reliable management of solar/optical properties of the
building envelope that has rarely been
consistently and economically achieved in
buildings. Some of the technologies to
Summer 2006 17
Feature
All That Glass?
Is there an appropriate future for double skin façades?
By Donald B. Corner,
Professor of Architecture, University of Oregon
INTRODUCTION
Building techniques have been shared
across the Atlantic Ocean for hundreds of
years. Anglo-American settlers preparing
to move westward into the Appalachians
were fortunate to have learned about log
cabins from Scandinavian immigrants. Standardized 2x4 light frame construction traveled from the United States to Europe and
returned much later as the Swedish factory crafted house.
In recent years we have seen the first
landings of a new import, the double skin
façade. American architects are attracted
by the appearance and the performance of
double skins, even though the benefits are
hard to quantify. They will pursue this new
option despite a growing body of technical
literature that questions the effectiveness
of the form (Lee, LBNL, 2006). We have
had the same experience with the opening
example of industrialized housing.
There is a field, littered with well documented failures, that designers visit again
and again because it is so seductive in concept, if not reality. The double façade is an
equally powerful concept. Thus, American
architects will try on these new enclosures, and their reasons for doing so will
be as varied as they have been in Europe.
As in Europe, their motivations will go beyond effective control of daylight and thermal comfort.
This narrative examines frames of reference that have shaped European applications of the double façade and from this
body of experience, outlines a critical perspective on the future of this technology in
the United States.
A SUMMARY OF DOUBLE SKIN TECHNOLOGY
Double skins are multiple leaf wall assemblies in the transparent or largely
transparent portions of a building façade.
They range from the vernacular storm
window to the closely coupled, all glass
façade that is the focus of this paper. Double skins of any form include an outer
façade, an intermediate space and an inner
façade. The outer leaf gives the building
weather protection and acoustic isolation
where high noise levels are present on the
exterior. The intermediate space can be
used to buffer thermal impacts on the interior. Through the use of open slots and
operable dampers in the glass planes, it is
possible to ventilate the interstitial space
on warm days and admit sun warmed air
to the interior rooms on cool days. In
most cases operable shading devices are
placed in the intermediate zone where
they are protected from damage. Double
glazing of the inner façade provides the
optimum thermal barrier, while single glazing of the outer façade is sufficient to create the buffer space.
Double skins require the designer to
sort through an imposing array of choices.
A decision tree must include the following
fundamental questions:
• How much of the outer façade is glass
and what is the relationship of that glass
to the primary structure and to the
other elements of building enclosure?
• What types of control are needed over
the passage of light, heat, air and sound
at the transparent portions of the
façade?
• How will the two façade layers and the
space between them be developed in a
rational and effective construction
strategy?
• How will access be provided to clean
the glass and maintain the operable
components located inside the buffer
space?
An expansion of these basic points,
prepared by this author, will appear in the
forthcoming The Green Studio Handbook
(Kwok and Grondzik, in press). Case studies and details can be found in widely distributed European texts (Herzog et. al.,
2005 and Oesterle, 2001).
PLACE AND CULTURE
As elements of architecture, enclosure
Figure 1 - Office Block Remodel, Stuttgart, Germany, 1996. Behnisch Sabatke Behnisch.
Summer 2006 19
systems have a significant and fascinating
cultural component. Façade openings in
Europe have always had numerous “switches” in them, operated by the building
Figure 2 - Hannover Messe A.G., Hannover, Germany,
1999. Thomas Herzog + Partner.
Figure 3 - Helicon Building, London, UK, 2000. Sheppard
Robson International.
Figure 4 - Plantation Place, London, UK, 2005. Arup Associates. Architects.
20 Journal of Building Enclosure Design
user. Traditional windows in Italy have an
outer layer of louvered shutters, glass in a
casement sash, light filtering curtains and a
solid inner shutter of wood. Each can be
deployed to block, filter or admit elements
of the exterior world. In the United States
we have used building technology to eliminate switches, as insulating glass eliminated
the storm window.
European double façades are expanding the benefits of switches, using technology to automate rather than eliminate
them. In commercial buildings a large percentage of the glass remains operable with
building ventilation coming directly
through the façade. The first new applications of double skins were “re-wraps” of
existing buildings, such that the operable
outer leaf works in tandem with the original façade to enhance building performance through both the heating and cooling
seasons (Figure 1). This strategy remains
one of the most cost effective applications
of the double skin.
From these beginnings, the new
façades rapidly progressed to become
spectacularly intricate machines that contribute to a wide variety of building climate
functions. Thomas Herzog’s Hannover
Messe A.G. is a mature example of a “corridor façade,” with the inner glass leaf set
back on the floor slab around the entire
perimeter of the occupied space (Figure
2). The façade expression is dominated by
its role in the ventilation scheme. With the
service cores removed from the central
block, the buffer space accounts for 22 per
cent of the remaining slab area. This is an
investment in passive strategies that few in
the U.S. would be willing to consider.
The quality and performance expected
of German buildings is part of their culture
and manifest in their regulatory system.
Office buildings must provide workers
with daylight and fresh air through an operable window within a specified distance
from each station. German texts make it
clear how these requirements have fueled
the development of double skins (Oesterle, 2001). However, as energy conservation goals have risen, all the components
and systems have improved and the potential for savings through the addition of a
second skin has become less. As the examples will show, German architects have become more focused and strategic in their
use of the double façade.
THEMES OF PRACTICE
In London, the exuberant use of technical systems has long been part of the commercial building culture. The Lloyd’s Bank
(1986, Richard Rogers) and the New Parliamentary House (2000, Michael Hopkins)
both have ventilated façade cavities in addition to their more famous expressive elements. The engineers and architects at
Arup and Arup Associates have had a
formative influence on “high tech” work.
Using extruded sections and machined fittings, in the 1980’s Arup crafted robust
and expressive external shading devices
that cantilever off the building façade (One
Finsbury Avenue, London, UK, 1984, Arup
Associates). The work of Peter Rice added
large expanses of suspended glazing to the
British vocabulary. Once these two themes
of practice were firmly established, the
double skin became a logical progression.
Adding a glass leaf to the outside face of
the cantilevered shading structure allows
the fixed louvers to be exchanged for
much more effective operable systems and
admit diffuse light on overcast days and
track the sun when shading is an issue.
The Helicon Building in London offers a
dramatic example (Figure 3). Engineered
by Arup, the building has a monumental
double façade suspended over the south
entry. Inside the stack ventilated cavity are
gigantic louvers. Not far away, Plantation
Place offers a different integration of the
two venerable themes (Figure 4). The
façades are made with a repetitive unit
curtain wall system. Close to street level
the modules are matched to suspended
external shades made of stone, in response to the context. As the floors
mount, the plan steps back to form twin
towers dominated by interactions through
the skin. The same façade unit develops a
cantilevered cavity with maintenance access and an outer leaf of glass shingles that
are open jointed to discharge the heat absorbed in the small scale, operable louvers.
This building does not function in all the
modes of the German examples, but it
also has far fewer moving parts. It is part
of the trend in which architects are trying
to capture the major benefits of a double
skin through more efficient means.
BRAND IDENTIFICATION
The Arup offices in London occupy a rehabilitated building with a double skin
façade at the street corner. It is therefore
one of the most potent of motivations,
marketing. Arup is projecting a contemporary image of the environmentally responsive building that has enormous appeal to
corporate clients. Returning to the Helicon
Building, with the monumental façade, one
must note that other faces are tempered by
a much more reserved version of the same
thermal chimney approach. The core of the
building receives its light from an atrium
space. The huge system above the entry
hangs in front of a shallow band of offices
no greater in volume than the façade cavity
itself. That this flamboyant gesture survived
the hard sums of a commercial project is a
testament to the power of brand identification and the role of the double skin in realizing that ambition. Another vivid exemplar
is a building on a prominent site in central
Stuttgart (Figure 5). It has the shape of a
teardrop with the pointed end reaching out
toward a main thoroughfare. The plan becomes so narrow that fully one third of the
outer glass leaf has nothing behind it except
the cavity space.
THE UNIVERSAL, ALL GLASS FAÇADE
The RWE headquarters in Essen is a
beautiful cylindrical tower that is considered by many in the field to be the most
elegant of double skin façades (Figure 6). It
faithfully realizes the historic imagery of
Mies Van der Rohe’s project for an all glass
skyscraper and strives to develop the
“neutralizing wall” advocated by Le Corbusier many years ago. This building, and
others like it, are driven by a renewal of
modernist theory, now with the technical
means available to try to realize those visions. The Essen tower is defined as a corridor façade, segmented at each floor
plate. It is also a unitized, double curtain
wall with cross-over ventilation between
adjacent cells so that the intake and exhaust air streams are separated. The
façade elements demonstrate a commitment to repetitive production, although
they are so precise and intricate they
should in no way be referred to as economical. The cylindrical shape optimizes
the surface to volume ratio, but it also
makes the building indifferent as to solar
orientation. This is the double skin proposed as a universal solution that can be
deployed with equal enthusiasm to the
north, south, east or west.
There is, in Frankfurt, a newer tower
that makes an interesting comparison (Figure 7). The work of Schnieder + Schumacher responds to the modernist legacy
with equal intensity. Here the glass cylinder is pure, without accessory elements at
the top or the base. The original concept
called for buffer spaces that would ascend
in a spiral similar to Norman Foster’s
“Gherkin” in London (Swiss Re, 30 St.
Mary Axe, 2004). In Frankfurt, the building
has no major tenant to foot the bill and
double skin techniques are reaching down
into a speculative market that demands
greater efficiency of means.
As constructed, a square floor plan
with a very simple glass façade is developed inside the protection of the outer
cylinder. The difference between the two
shapes produces four segmental buffer
spaces, two in front of partitioned offices
and two as “winter gardens” outside of
open desk space. The cavities are segregated every four stories by a full circular
floor plate. The outer leaf, executed skillfully by Gartner, has operable units in the
upright triangles of the ornamental façade
pattern. These ventilate the buffer spaces
on demand. The scheme is beautiful in its
conception, but again indifferent to solar
orientation; a triumph of theory over the
realities of nature. The cylinder is once
more proposed to minimize surface area,
but since the building is so often in cooling
mode, a concern for skin losses is a suspicious motivation.
GREEN ARCHITECTURE
The double skin takes a different role
on the palette of architects who try to
connect to nature rather than neutralize it.
Exemplary of this approach is the work of
Behnisch, Behnisch and Partner, with climate engineering by the well known firm,
Transsolar, also of Stuttgart. This team has
worked closely on a number of projects
including the NORD/LB headquarters in
Hannover, Germany (Figure 8). For
Behnisch and Transsolar, the double skin in
not a preconceived solution, but just one
of many tools taken up in order of their effectiveness. In fact, the double skin may be
quite far down that ranked list.
At NORD/LB the first concern is connecting the building occupants to the richness and variety of the environment outside the glass. This includes views, ample
Figure 5 - Landesbank Baden Wurtemberg, Haus 5+6,
Stuttgart, Germany, 2004. Wohr Mieslinger Architekten.
Figure 6 - RWE A.G., Essen, Germany, 1997.
Ingenhoven Overdiek Kahlen and Partner.
Figure 7 - Westhaven Tower, Frankfurt, Germany,
2003. Schneider + Schumacher.
Figure 8 - Norddeutsche Landesbanke (NORD/LB), Hannover,
Germany, 2002. Behnisch Behnisch and Partner.
daylight and natural ventilation through
windows controlled by the occupants. A
slender ring around a generous courtyard,
NORD/LB has extremely shallow floor
plates, even by German standards. Portions of the building have offices on only
one side of social corridors. With the use
of glass partitions, a spectacular quality of
light washes through the building at all
times. This is an architecture that intends
to maximize the skin to volume ratio, not
minimize it.
Double skins at NORD/LB have been
22 Journal of Building Enclosure Design
used in only two zones, and in both cases
for very specific reasons. First, they have
been applied to the long face of the building where needed to block traffic noise
from a multi-lane boulevard. This again is
driven by German space quality standards
and sound walls are recognized as one of
the corollary benefits that justify the double envelope (Osterle, 2002). A second
application has been made on the southwest face of the 16-storey tower that was
added to the scheme to provide offices
for the board of directors. The entire
building is fitted with automated, external
shading louvers. At the higher levels these
shades would often be forced to retract
into their shelters on windy days if it were
not for the protection offered inside the
buffer space. The afternoon heat gain
through this one exposure on breezy
summer days was considered unacceptable, motivating the second leaf of glass.
At the lower levels, where wind velocities never reach the critical level, the external louvers are free to deploy as needed. Where a covering layer of glass is not
required by wind or acoustics, none is applied. This clearly demonstrates that in
the climate of central Europe, shading is
the design issues, not thermal losses, even
for a building with such an extensive surface. There is an interesting cultural footnote. On the quiet streets of this German
town, shading louvers can extend all the
way down to the sidewalk without any
sign of damage. In the United States we
might need the outer glass just for protection from vandalism.
The sound wall at NORD/LB happens
to occur largely on a north face, so the
double façade there returns little benefit
in the dissipation of heat. However, it
does have a second role in providing fresh
air to offices that would otherwise face
auto exhaust. The large interior courtyard
of the building is a reservoir of clean air.
This air is drawn through a flat plenum
under the lowest office level. (Corresponding to the white volume at the base
of the detail: Figure 9). In the relevant
sections, baffles direct air into the base of
the façade cavity and it is drawn by stack
effect through louvers at the top of the
façade. The occupants are then free to
enjoy a clean and quiet source of fresh air
through the operable windows of the
inner skin. This simple transformation
eliminates the need for vent panels in the
sound wall; openings that would compromise the acoustic performance.
Transsolar also teamed with Allmann,
Sattler, Wappner on the design of an office
complex in Munich (Figure 10). A low rise
element again wraps the edge of the site
with a really robust sound wall against the
autobahn. There is an office tower in one
corner with a more conventional form
than NORD/LB. The scheme demonstrates a full palette of environmental
strategies: shallow floor plate with easy ac-
cess to the perimeter, concrete structure
with radiant cooling, operable glazing
across the entire façade, displacement
ventilation using a podium floor, a wind
driven exhaust stack and a fan assisted
supply sharing the same vertical shaft, an
evaporative cooling tower on the roof operated at night, ground source wells operated during the day. Air flows in the
rooms are boosted by small fan coil units
at the perimeter that fit under the podium
floor. These are fed with hot and cold
water but no air duct system is required.
Munich has district heating so there are
no on-site strategies for that side of the
energy equation.
Fitting in among these strategies is a
double façade for the tower. It is so simple in its concept and crisp in its detailing
that it could easily be mistaken for a single
leaf assembly (Figure 11). The façade is a
unitized curtain wall with an overall depth
that is not much greater than standard
wind mullions. The inner leaf of insulating
glass is divided at chair rail height into two
operable units. The cavity is partitioned at
the same point and contains operable
shading louvers in the upper region. The
outer leaf is a perforated stainless sheet in
the lower zone and plate glass above.
Generous amounts of ventilation air can
be taken through the perforated metal by
opening the lower sash. The larger, upper
sash is the vision zone and the true double
skin. By simply allowing the perforated
metal to overlap this unit slightly at the
top and the bottom, there is free ventilation of the cavity behind the outer leaf of
glass. This can be used to dump heat gain
from the shades or to admit a moderated
air flow by opening the upper sash behind
its protective outer leaf. It was first
thought that projecting fins would be
needed to create turbulence and to ventilate the cavities. Flow modeling revealed
that the strips of metal mesh, top and bottom, were adequate on their own.
It is remarkable how simple this double skin system has become. The key to
the scheme is that maintenance access
comes through the fully operable inner
glass leaf. In the United States, this would
in itself be a very radical proposition, but
in Germany a large percentage of operable glass is a given in the building culture.
For visual continuity, the low rise portion
of the complex has the same cladding
units on the courtyard façade, except that
the outer leaf of glass in the upper zone is
omitted. This repeats the lesson that protection of the external shading devices
from wind velocities at height is the primary motivation for the double skin. Allmann, Sattler, Wappner and Transsolar
have identified the performance attributes
that are needed from the façades and
achieved these with directness, clarity and
true elegance.
EXPLORATIONS IN THE AESTHETIC DOMAIN
The technical benefits of the glass double façade have not yet been established
with the certainty of those for the rainscreen wall. Nevertheless, we have already seen that, like the rainscreen, the
double skin is a trigger for aesthetic explorations that run far beyond the functional
basis of the concept. Herzog and De Meuron, Swiss architects of the first rank,
completed very sophisticated double
façades early in their rise to international
prominence. Their “re-wrap” façade in
Basle (SUVA Building, 1993) is a marvel of
piston actuators and glazing technology.
By contrast, their Laban center for Dance
in London (Deptford) is wrapped in a simple layer of polycarbonate panels (Figure
12). The wall section displays all of the attributes of a double façade: open grills at
the base, operable vents at the inner leaf
that draw air from the cavity, maintenance
gangways between the skins that so far
have seen limited use. But, these are not
the driving forces behind the design. Subtle tinting of the polycarbonate gives the
flush façades an abstract, lyrical quality as
they hover above an earthy, post industrial
context. Inside, the dance studios receive
a serene wash of colored light so beautiful
that the 2003 RIBA Stirling Prize could
have been won for this effect alone (Figure 13).
The tour de force of glass façades remains Peter Zumthor’s Kunsthaus, Bregenz (Figure 14). Here the building is clad
from parapet to ground plane with identical laminated panels. No other material is
present except for the front door and the
stainless steel brackets that support the
glass. Inside is an equally minimalist structure. Each gallery fills a floor, with art displayed against the turned up edges of concrete “trays” that are suspended three
times above one another like memo boxes
Figure 9 - East façade detail, NORD/LB. Behnisch Behnisch
and Partner.
Figure 10 - Münchner Tor, Munich, Germany, 2003.
Allmann, Sattler, Wappner.
Figure 11 - Façade unit, Munchener Tor. Allmann, Sattler,
Wappner.
Figure 12 - Laban Centre for Dance, Deptford, UK, 2000.
Herzog & de Meuron.
Figure 13 - Studio interior, Laban Centre. Herzog & de
Meuron.
Summer 2006 23
contemporary response to the expectation that a house for art should itself be
art. So great has been the acclaim for this
aesthetic that the use of open glass shingles has in return influenced more traditional double skins like that at Plantation
Place in London or the Deutsche Post
Tower in Bonn (2002, Murphy/Jahn).
Figure 14 - Kunsthaus, Bregenz, Austria, 1997. Peter
Zumthor.
Figure 15 - Genzyme Center, Cambridge, MA, USA, 2003.
Behnisch Behnisch and Partner.
on the corner of your desk. Light
penetrates the building at the tall interstitial spaces and filters into the galleries
through a translucent glass ceiling. The
façade cavity contains the steel framing
necessary for the outer leaf of glass and
extends below grade to light staff space in
the basement. There are operable shading
devices in the void, but the light levels
across the ceilings drop off so quickly it is
not clear how much shading is really needed. However, this is not a façade to be
measured with instruments. The outer
glass shingles overlap side-to-side and
overhang top to bottom, producing a prismatic surface that is endlessly fascinating as
the sun moves across the sky. While the
interior defers completely to the featured
works of art, the exterior represents a
24 Journal of Building Enclosure Design
CONCLUSIONS
There are certainly major themes that
drive the design of glass façades: optimize
the harvest of daylight to reduce lighting
loads, reduce thermal gains in buildings
that are almost always in a cooling mode,
and perhaps control surface temperature
at the inside face of the glass to maintain
human comfort. A comprehensive analysis
of costs and benefits in a double skin is difficult because it touches virtually every aspect of the building, from structural form
to occupant behavior. Andrew Hall, head
of the façade engineering group at Arup,
cautions that double skins, in and of themselves, rarely save money or energy (referenced in this discussion was the seminal
article by Gertis, 1999). The façade concepts must result in significant savings elsewhere in the design. A dramatic reduction
in mechanical cooling equipment would be
one such contribution. Hall acknowledges
that there are also forces of market and
fashion that brush aside rational analysis.
He warns of architects who take the approach that, “in the double skin we have
the solution, now what was the problem?”
To advance appropriate building we
must have the patience and maturity to
use the double skin as a complement to
simple and logical controls of the building
climate. Even though it is an intrinsically
“natural” strategy, the double skin can be
abused, thrown in the face of nature just
as designers have done for decades with
mechanical cooling. We must deliberately
work our way down the list of green building strategies, applying the most effective
first and the double skin only in its turn.
NORD/LB shows us that the results can
be a rich environmental experience as well
as a good engineering solution. The Genzyme Center, also by Behnisch, is the best
American application so far, but the façade
systems were value engineered to the
point that they have little of the elegance
of the native German examples (Figure
15). We must recognize this weakness in
the American building culture. Facing our
energy future, we cannot afford to be reductive in our thinking. While it is fair to
demand true performance, we must also
be willing to make pioneering investments.
Over the history of architecture, the building façade was never meant to be inexpensive. It holds far too much importance,
both technically and culturally. We must
allow ourselves well reasoned excursions
into the aesthetic domain. These have the
power to inspire creative research into the
effective means of architecture.
ACKNOWLEDGEMENT:
The interviews and site visits that form
the basis of this article were funded by the
John Yeon Center for Architectural Studies
at the University of Oregon.
INTERVIEWS:
• Thomas Auer, Transsolar, Stuttgart,
May 2005.
• Peter Clegg, Feilden, Clegg, Bradley,
London, April 2005.
• David Cook, Behnisch Behnisch and
Partner, Stuttgart, May 2005.
• Andrew Hall, Arup Façade Engineering,
London, April, 2005.
• Stefan Holst, Transsolar, Munich, May
2005.
• Mikkel Kragh, Arup Façade Engineering, London, April, 2005.
• Martin Werminghausen, Behnisch
Behnisch and Partner, Boston, August,
2005.
REFERENCES:
• Gertis, Karl. “Sind neuere Fassadenentwicklungen bauphysikalisch sinnvoll Teil 2: Glas-Doppelfassaden (GDF)”
Bauphysik, Heft 2/1999. Berlin: Ernst
and Sohn, Wiley-VCH, 1999.
• Herzog, Thomas and Roland Krippner,
Werner Lang. Façade Construction Manual. Basle: Birkhauser, 2004.
• Kwok, Alison and Walter Grondzik.
The Green Studio Handbook. Oxford:
Architectural Press, in press.
• Lee, Eleanor and Lawrence Berkeley
National Laboratory. “High Performance
Commercial Building Façades.” Public
Interest Energy Research Program: CEC
500-2006-052-AT15. Sacramento: California Energy Commission, 2006.
• Oesterle, Eberhard. Double Skin
Façades. Munich: Prestel, 2001.
■
Feature
Architectural Glazing for Sound
Isolation (an Acoustician’s Perspective)
By Jeffrey L. Fullerton, Acentech, Inc.
ABSTRACT
For most buildings, glazing is selected
for its thermal or optical performance.
However, there are numerous buildings
where exterior noise impacts are a factor
in whether the interior space will function
properly. Often, the most important element for reducing intrusive noise is the architectural glazing. This paper discusses
the acoustical tests and ratings of glazing
systems, various upgrades to architectural
glazing and several case studies where improved sound isolation from exterior
noise was achieved using architectural
glazing.
INTRODUCTION: ACOUSTICS 101
Sounds propagate through the air as
pressure waves. Normal human ears are
sensitive to a wide range of varying sound
pressure. To simplify the representation of
these acoustical pressure waves, the pressure levels are represented in a logarithmic ratio expressed in decibels, or dB.
Human ears are more sensitive to midand higher- pitched sounds (the “treble”
component), compared to lower frequency sounds (the “bass” component). This is
represented by the so-called A-weighting
filter for measuring sound, noted as decibels, A-weighted, or dBA.
Since sound levels are reported in logarithmic decibels, they
are inherently
non-linear.
As a result, comparing the loudness of
various sounds may not be as simple as it
appears. For example, studies of human
responses to sound levels have shown
that changes of 3 dB are considered a
“just noticeable difference” and changes
of 5 dB are considered to be “significant”.
Changes of approximately 10 dB are perceived as a “doubling” of the sound level.
A 20 dB change is perceived as being
“four times louder”.
To provide some perspective on various sound levels, the following environments or sound sources are described
below.
Rural Neighborhood: 30 to 40 dBA
Urban Neighborhood: 40 to 50 dBA
Speech (at 3ft): 55 to 80 dBA
Traffic (at 100ft): 65 to 80 dBA
Aircraft Overflights: 65 to 110 dBA
ACOUSTICAL PERFORMANCE TESTING AND
RATINGS
The two primary types of acoustical
tests for exterior glazing are either conducted in 1) a laboratory; or 2) in an installed condition, referred to as a
field test. Based on these two
types of tests, there are two ratings for quantifying the acoustical
performance of glazing systems.
1) Laboratory testing
Laboratory testing is intended to provide a standardized and repeatable test of a
building construction relating to
its performance for sound transmission. The tests are standardized by ASTM E90-04, where all
of the details regarding the laboratory, the test specimen, the test protocol, test conditions and measurement
procedures are specified. The thoroughness of the standards is intended to pro-
26 Journal of Building Enclosure Design
vide test results that are comparable and
repeatable in any laboratory that meets
the ASTM standards. A list of laboratories
accredited by the National Voluntary Laboratory Accreditation Program is available
at the National Institute of Standards and
Technology website: www.nist.gov.
There are a number of strengths and
potential weaknesses to the results gathered from laboratory testing. It is important to understand that laboratory tests
are generally conducted on a particular element of a building construction, rather
than an entire composite construction.
For example, manufacturers often test individual elements such as windows or
doors in order to demonstrate their product’s specific sound transmission performance. While it is often useful to know the
relative performance of one product versus another, it is often more important to
relate that performance to the other elements of the façade in order to understand the performance of the composite
construction. Also, keep in mind that laboratory tests are conducted under ideal
conditions. Accordingly, the results from
laboratory testing are generally considered to be the ideal performance of that
product, and may not be as achievable
when installed by a typical contracting
crew. These considerations should be
considered when applying laboratory test
data to a specific project.
2) Field testing
Field-testing provides a means of conducting a test of an actual, installed construction. In most cases, these tests measure the performance of the entire façade
rather than a particular element in the
façade, though this is also addressed in the
field test standard methodology. The field
tests are standardized by ASTM E966-04,
where all of the details regarding the installation, sound source, test protocol,
test conditions and measurements are
specified. The standard is intended to provide a methodology for comparing the
test results to laboratory results or other
field tests that are conducted to the same
standard.
The most significant strength to field
testing is how the installed product performed. Depending on the quality of installation of the test specimen, the
performance may closely represent what
might be expected for a typical installation
of that particular composite construction.
Ratings of glazing systems in this range and
higher may be adversely impacted by the
incorporation of a window framing system, which often degrades the performance.
ACOUSTICAL PERFORMANCE RATINGS
The results from the sound transmission tests can be reduced to several single
number ratings. The most commonly used
ACOUSTICAL UPGRADES FOR
rating is the Sound Transmission Class
ARCHITECTURAL GLAZING SYSTEMS
(STC), determined by ASTM E413-04.
Architectural glazing can vary dramatiThis rating is determined by comparing
cally in sound isolation performance. The
the sound transmission loss data from the
following sections describe a variety of diftest results to a weighted transmission
ferent window glazing options with differloss spectrum that represents the STC
ent acoustical performance.
contour. The one drawback of the STC
1-inch thick insulated glazing unit:
rating is that it assumes a sound source
In many areas of the country, a common
with a spectrum similar to human speech.
glazing assembly that is used on commerFor this reason the STC rating is often a
cial projects is a 1-inch thick insulated
poor predictor of sound isolation for low
glazing unit, consisting of 1/4-inch thick
frequency sources such as music, mechanlites separated by a 1/2-inch thick airical system or transportation noise (see
space. This glazing generally provides a
below). An example of test data comlaboratory rating of about STC 35 and
pared to the STC contour is shown in FigOITC 30, though depending on the frame
ure 1.
it is installed in, the ratings may decrease
More recently, another rating was deby a few points. This glazing provides acveloped which is called the Outdoor–Inceptable sound isolation from exterior
door Transmission Class (OITC). The
noises in rural or quieter areas, or when a
methodology of this rating is defined in
moderate amount of intrusive noise is acASTM E1332. This rating is determined by
ceptable.
calculating the difference between the
Insulated glazing unit with glass
product’s sound transmission loss perpanes of different thicknesses: An alformance and a standardized exterior
ternate 1-inch thick insulated glazing unit
source spectrum. The standardized
spectrum is an average of three transportation spectra: a freeway, a railroad passby and an aircraft takeoff.
The resulting number is intended to
relate to the perceived sound levels in
the interior receiving space as the result of an impact from a transportation
source. At this time, this rating is not
as widely used as the STC rating,
however, it can often be calculated
provided that sound transmission loss
data for a product is available.
There are several publicly available
acoustical performance data sets for
glazing. The two most common data
sets are provided by Solutia (a Monsanto company, formerly named
Saflex1) and Viracon. These data sets
provide the performance of only the
glazing systems, without a window
framing system. As a result, these data
may somewhat overestimate the performance of a window product with a
frame, particularly when the STC ratings of the glazing exceed STC 40. Figure 1
Summer 2006 27
could consist of lites that have different
thicknesses. For example, one lite might
be 1/4-inch thick, while the other might
be 3/16-inch thick, resulting in a 9/16-inch
airspace. Laboratory test data indicates
that this glazing unit can achieve a slightly
higher STC rating of 37. This is attributed
to a reduction of the resonance of the system by using the different thickness lites.
However, it is interesting to note that this
window achieves the same OITC rating
(OITC 30) as the previous 1-inch insulated
glazing. This would suggest that the increased performance indicated by the improved STC rating may not be noticeable
to an occupant, if the exterior noise
source is similar to the OITC standard
spectrum.
Insulated glazing unit with laminated glass: Another alternate of the 1inch thick insulated glazing unit could
comprise one lite that is laminated. The
laminated lite could be 1/4-inch thick and
be used in combination with another 1/4inch thick lite separated by 1/2-inch to
create a 1-inch thick glazing unit. Laboratory test data achieves an STC rating of
39. This is also attributed to a reduction of
the resonance of the system by using the
laminated pane, which is a damped system. As with the previous example, it is
interesting to note that this window
achieves only a slightly improved OITC
rating (OITC 31). The perceived difference of this glazing unit compared with
the previous examples may not be noticeable to an occupant.
Of practical interest, it is recommended that for acoustical reasons the laminated lite be installed on the interior of the
glazing unit. This arrangement allows the
lamination to remain closer to the occupied temperature, at which the lamination
performs more effectively. Laminated
panes that are subjected to colder temperatures perform similarly to non-laminated panes of glass.
Insulated glazing unit with larger
airspace: When the thickness of the window unit can exceed 1-inch, other options
are possible for improving the sound isolation performance. For example, a 1-inch
deep airspace between two 1/4-inch thick
lites can improve the acoustical performance to a rating of STC 37; the OITC rating remains at 30, indicating that the perceived difference to the occupant may not
28 Journal of Building Enclosure Design
be significant. The drawback of such a
system is that the thicker insulated window unit may require a different (potentially non-standard) framing system to install this glazing unit. As a result, this may
not be a cost-effective improvement to
consider.
“Storm sash” upgrade: In many remedial projects, it is not possible or costeffective to remove the existing window
to improve the sound isolation. Many
times the most effective solution is to introduce a secondary window system that
captures an airspace of two-inches or
more with respect to the existing window. Many people consider such an additional window akin to a “storm sash”. This
type of upgrade can be performed on the
exterior (if space allows) or interior (if the
exterior of the building cannot be modified).
With this upgrade, the airspace between the existing and new windows is a
significant factor that largely determines
the amount of sound isolation improvement that may be possible. It is suggested
that airspaces of two-inches are the least
that should be considered, but larger airspaces can provide even greater benefits.
The thickness of the secondary sash is
generally not considered as significant a
factor. Testing on a recent project demonstrated that with an airspace of 5 inches, a
1/4-inch secondary pane was the most
cost-effective upgrade to implement2. The
acoustical performance of systems that include the secondary sash can start at STC
40 and OITC 33 and may even achieve
higher sound isolation performance depending on the construction of the façade,
depth of the airspace, or thickness of the
secondary glazing.
Potential issues to consider with
upgrades: Acoustical upgrades to window systems can occasionally introduce
the following detrimental effects: trapped
condensation, thermal performance reductions, the need for heat treating of
glazing, and difficulty in cleaning.
Trapped condensation can result in any
window systems that are not well sealed.
This results from humidity entering the
airspace between the two panes of glass
and condensing on the cooler surface.
The magnitude of the condensation is dependent on the humidity and temperature
differences across the glazing system. It is
occasionally possible to control this effect
by using the building’s HVAC system to
maintain a lower humidity level. Alternatively, it is also possible to introduce passive airflow vents for the cavity between
the window system to maintain airflow
that will minimize the condensation.
The thermal performance with a secondary window system can decrease with
larger airspaces. This is due to convection
within the cavity transferring more of the
heat to the colder surface and with a larger airspace, the convection can become
more effective. Studies have shown this
convection can reduce the thermal effectiveness of the window system.
Airspaces between windows can trap
heat that may build up to excessive levels
within the cavity. As a result, manufacturers and installers often recommend heat
treating the lites that create the cavity.
This heat treating introduces a residual
surface compression in the glass, which
improves its ability to resist breakage
from thermal stresses [citation WBDG].
The drawback of heat treating is the additional cost for the project.
A practical issue with acoustical upgrades relates to cleaning the cavity between the two window systems. Typically,
installed secondary window systems are
not sealed and therefore present the potential for dust and dirt to enter the cavity.
To clean within this cavity, it is necessary
to allow for the secondary lite to be operable or removable. It is important to devise or select an operable or removable
system that maintains a reasonable seal
around the secondary sash when it is not
being cleaned. Tests have demonstrated
that cam locks and continuous hinges can
provide the means to allow for the secondary sash to be operable and maintain a
good acoustical seal.3
CASE STUDIES
The following case studies all involve
acoustical upgrades of window systems.
They include projects at an extended stay
hotel in an urban setting, commercial office space under a runway departure, and
a residential development under a runway
departure.
Extended stay hotel in an urban
setting: The patrons of the hotel were
complaining of being awakened by construction activities in the neighborhood,
which began early in the morning. They
were also complaining of late night bar patrons causing a commotion when they left
the bars in the late evenings and early
mornings. The hotel did not want to have
any more disappointed guests or continue
to foot the bill for refunds.
The existing window systems consisted of operable double hung aluminum
windows with 1-inch thick commercial
grade glazing. The dimensions of the windows were about four feet wide by about
four feet tall. The windows were mounted within sills that included an additional
five inches inside the guestroom. The exterior of the building was an old masonry
construction within interior stud framing
and drywall. This substantial façade construction meant that the sound isolation
weakness was the windows.
The deeper than average sills provided
a good amount of space for mounting secondary window systems inside the guestrooms. With this arrangement, the exterior of the building was not impacted
visually, which helped the project avoid
any review by the local architectural
board. Testing after the installation
demonstrated a substantial improvement
of the sound isolation. The overall noise
reduction was measured to be approximately 7 to 10 dB better, which was perceived to be a noise reduction of 35 per
cent to 50 per cent. This dramatically reduced the complaints from the guests,
which greatly satisfied the hotel managers.
They now market their guestrooms as
providing superior sound isolation from
the surrounding urban environment.
Commercial office space under a
runway departure: A new commercial
office building was constructed in an area
that had been previously used for industrial facilities. The site was less than one mile
from a runway with the departure flight
track passing directly over the building.
Shortly after initial occupancy, tenants
began to complain about noise. The noise
from the departures was interrupting
phone conversations and meetings. The
developer requested a sound isolation upgrade that would provide effective sound
isolation, but, at the same time, be as affordable as possible.
A study of the noise impact yielded interesting results. It was learned that the
runway operated infrequently under
unique wind conditions that occur mainly
in the spring and fall. In total, the runway
was used for only about 15 per cent of
the departures during the year. While this
infrequent usage may seem to be a benefit, it was actually a detriment since it resulted in very intense use during those
short periods. When these unique prevailing winds occur, every departing flight
would use this runway, which meant that
aircraft were passing over the site approximately every three to five minutes. This
frequent departure schedule was particularly distressing to the tenants. Another
interesting find from the complaints was
that the noise was most bothersome on
the side of the building that saw the backside of the planes as they departed; the
occupants who would watch the planes
approaching the building were not adversely impacted by the noise of the overflight.
There were several significant issues
relating to implementing the upgrades.
The recently completed building was already partially occupied at the time of this
work. This presented complications for
accessing the windows, performing the
upgrades and scheduling the work. Fortunately, the second of the two building that
comprised the project was still in design,
so the window upgrades being considered
could be incorporated in the construction
plans from the start.
The base building windows were a 1inch thick insulated glazing unit in individual window frame systems, or in two sections of curtain wall. The exterior façade
of the building consisted of masonry with
an interior stud construction, resulting in a
fairly effective sound isolating construction.
To determine the most cost-effective
upgrades, in-situ testing was proposed
with three different potential upgrades to
be considered. The 3 interior sash options
that were tested included a 1/4-inch thick
annealed lite, a 1/4-inch thick laminated
lite and a 3/8-inch thick annealed lite. A
secondary framing system was installed
within the existing window system to
allow for quick changes between the various options. The frame was located
where it achieved an airspace of five-inches from the base building windows. The
tests included cam locks and a continuous
hinged installation for facilitating the removal of the secondary lites.
The test results demonstrated that the
various options performed relatively similarly. The 1/4-inch thick annealed lite
achieved an improvement of about 10 dB,
while the 1/4-inch thick laminated lite
achieved a reduction of 11 dB, and the
3/8-inch annealed lite provided a 13 dB
improvement. The contractor assisted
with pricing the various options. The developer eventually determined that the
1/4-inch annealed lite provided the most
cost-effective option to implement. The
tests also demonstrated that the cam
locks provided slightly better performance over the continuous hinges. Based
on the locations of the complaints, the
upgrades were only performed on the
two façades that faced the departing jet
exhausts. The same upgrade was planned
for the future office building project during the design.
Residential Development under a
Runway Departure: A new residential
development was planned near the office
building project described above. Based
on the experience at the office buildings,
there was significant concern with locating residences in this area. The most significant concern related to the potential
for sleep disturbance due to late night or
early evening aircraft operations. There
was also concern about interference with
conversations and listening to TV and
music.
Unlike the office buildings, the developer was required to demonstrate that
their project would achieve an interior
sound level goal recommended by the
Federal Aviation Administration (FAA).
The goal was to achieve a yearly daynight average sound level (abbreviated
LDN) of no more than 45 dBA. The airport’s own noise contours indicated that
the proposed residential site was exposed to yearly day-night average sound
levels exceeding 70 dBA.
There were several complicating issues for this project. First, the annualized
average sound levels do not take into account individual flight events. It is entirely
possible to achieve the LDN 45 goal and
still have significant sound levels intruding
on the residence from individual departures. It was estimated that sound levels
of 70 dBA were possible from louder aircraft departures. This sound level could
result in sleep disturbance issues for the
Summer 2006 29
residents. Another concern from the developer’s perspective was the cost of
meeting this requirement.
In order to understand the noise impacts on the proposed site, an analysis of
over 1,500 aircraft operations was performed. These data provided a means to
relate the aircraft type, departure time,
departure height, and frequency of the
departures to determine a representative
sound spectrum at the exterior of the
building. This sound spectrum was applied to the various windows that were
being considered. Sound transmission
level data from various window manufacturers were used to determine the interior sound levels for selecting acceptable
windows for the project. This was compared to the sound isolation performance of the pre-cast concrete façade,
which provided relatively good sound
isolation performance for the non-glazed
portions of the façade.
The noise study and the discussions
with the window manufacturers provided several useful results. First, it was
possible to achieve the interior sound
30 Journal of Building Enclosure Design
level goal with typical commercial grade
glazing by limiting the size of some windows (the smaller window sizes reduced
the exposure of the interior space to the
aircraft noise). Second, the upgrades
were installed in standard window framing systems to minimize the cost of the
upgrades, as non-standard framing is
often considerably more expensive.
Third, the upgrades typically included
laminations or deeper airspaces to
achieve the interior sound level goal.
Post-construction testing has demonstrated that the window performance is
consistent with the program goals for
noise reduction. Subjectively, aircraft departures were perceived as relatively
quiet and unobtrusive to the residents.
There is an interest in surveying the occupants to understand their day-to-day
experience and perception of the aircraft
noise impacts.
CONCLUSIONS
Architectural glazing can be selected
to provide improved sound isolation for
interior occupants of buildings. There are
several existing standards for performing
laboratory and field-testing, which includes the derivation of single number
ratings (STC, OITC) for the test specimens. Various upgrades for improving
the acoustical performance of glazing
systems can be considered. There are
several concerns to keep in mind and
avoid when considering upgrades to window systems. These include glass thickness and type, and the depth of the airspace. Several case studies demonstrate
that the use of architectural glazing can
successfully improve the sound isolation
for building occupants.
REFERENCES
1. Monsanto/Saflex, Acoustical Glazing
Design Guide, 3.3-3.6, 1989.
2. Fullerton, J. and Najolia, D. “Aircraft
Noise Exposure along South Boston’s
Waterfront Development.” Proceedings of Internoise 2002, The 2002 International Congress and Exposition on
Noise Control Engineering, N400.
3. Whole Building Design Guide website: www.wbdg.org
■
Feature
Occupant Thermal Comfort
and Curtain Wall Selection
By Susan Ubbelohde, UC Berkeley
IN SUSTAINABLE BUILDING DESIGN,
ANNUAL energy use becomes a primary
metric for curtain wall performance. To the
extent that the curtain wall allows undesirable thermal transfer, whether through admitting summer solar radiation or through
winter heat loss, energy is used to counteract this transfer and keep the occupants
comfortable. Current rating systems for
sustainable performance, such as LEED™,
substantially reward reduced annual energy
use (USGBC 2002). State building codes
similarly emphasize annual energy use as a
primary metric of building performance.
Data from the state of California, however, indicate that energy costs in state
buildings are equal to only five per cent of
labor costs for the same buildings. This
means that a one per cent increase in productivity of state employees is equal to 100
per cent of the energy costs for the buildings that house those employees. If productivity can be related to occupant comfort,
such comfort issues will challenge energy
use as a primary measure of building performance.
Sustainable buildings are delivering
Figure 1 - View of the proposed building from the north
indicating the northwest curtainwall and roof-top photovoltaic array (rendering courtesy of the architect).
Figure 2 - (a) Full building section cut through NW and
SE curtainwalls and (b) Plan for typical office floor.
32 Journal of Building Enclosure Design
improved interior environments that result
in increased occupant satisfaction, which is
then reflected in documented increased
productivity, recruitment and retention. A
2003 report on sustainable building (Kats et
al. 2003) cites productivity increases of 5
per cent and absentee rates down 40 per
cent after employees moved into the renovated VeriFone building in Costa Mesa, California. Similarly, the Firstside Center Building in Pittsburg, Pennsylvania which received
LEED™ Silver Certification, reports increased productivity, reduced absenteeism,
better recruitment and significantly lower
turnover related to the improved interior
environment. The Herman Miller SQA in
Zeeland, Michigan, demonstrated increased
productivity and significantly increased employee satisfaction over the previous facility
(Herwagen 2000).
More specifically, occupant thermal comfort is highly valued by office building occupants and research shows that many buildings fall short. Thermal comfort and
acoustics are the only interior environmental
factors that receive a less than satisfactory
rating from 34,000 respondents in the Center for the Built Environment Web-based
Occupant Survey (Huizenga 2003 and Abbaszadeh 2006). Thermal comfort and ability to control indoor air temperature has
been ranked as the most important and
least satisfactory of interior environmental
factors in office buildings (BOMA 1999).
Occupant thermal comfort became a
critical issue in the recent design process for
a sustainable San Francisco, California office
building (Figure 1). During the schematic design phase, analysis identified cooling loads
as a major factor in building performance.
Specifications related to cooling loads and
energy use (Solar Heat Gain Factor, SHGF,
and Visual Transmission, Tvis) became a
prime factor in glazing decisions. However,
as the design team moved in the design development and contract document phases,
occupant thermal comfort during winter
months became a critical issue in the final
curtain wall design and specification.
SCHEMATIC DESIGN: COOLING LOADS AND
GLAZING SPECIFICATIONS
This sustainable office building of
267,000 square feet was designed for a
height constrained downtown site. The 11storey building fills out the volume of the
site, with typical floor-plates that average
140 feet by 184 feet around a central core
(Figure 2 a and b). This develops deep office
bays of 63 feet on the northwest and southeast orientations, with narrow bays 34 feet
deep on the northeast and southwest. The
floor to ceiling height, and therefore the
head height for the daylight glazing, is held
to 9 feet 10 inches due to height restrictions
on the site and the deep beams necessary
for the long spans. The northwest curtain
wall is canted and fully glazed, while the
northeast and southeast corners are developed as punched openings to reflect the design of the 1977 building to the northwest
owned by the client.
With the project tightly bounded in
terms of building massing and orientation,
the design team focused quickly on curtain
wall performance issues. To identify the relative factors in building energy use (for example, heating, cooling, lighting, solar radiation)
DOE2.1e modeling software was used for
parametric analysis of envelope thermal
loads. The input model described the entire
building and was well defined with architectural detail that included surrounding site
shading. A California Energy Code Title 24
compliant envelope was developed for the
base building. Hour-by-hour simulations of
nine zones per floor and ten floors of offices
were run with the San Francisco Typical Meteorological Year (TMY) climatic data (California 2005). While San Francisco is undeniably a temperate climate zone, local
conditions of fog, winter rains, cooling winds
off the Pacific Ocean, and three to five day
periods of “heat storms” caused by winds
DESIGN DEVELOPMENT: WINTER THERMAL
COMFORT
As the design moved into the DD phase,
the design team and the owner were interested in eliminating the perimeter heating
system. This would require maintaining the
interior surface temperature of the curtain
wall close to air temperature so that occupants near the window wall could remain
comfortable, including on cold winter mornings during building start-up hours. By
Cooling Loads
Typical Floor
25
6000
5000
20
4000
3000
10
kCal
15
MBTU
decreasing the overall U-value and thermally
breaking the frame of the curtain wall assembly, the interior surface temperatures of
the curtain wall could be controlled and the
mechanical system would not be required
to make up for radiant loss by the occupants
to the building envelope.
A full team including the architects, curtain wall contractors, glazing manufacturers,
the construction administrator, the general
contractor, daylighting and energy consultants, and a cost consultant developed a
range of curtain wall options for consideration. The glazing specifications that impact
cooling performance and daylighting (SHGF
and Tvis) were consistent for all options,
while the glass configuration, frame design,
overall U-value and costs varied across the
options. The U-values of the curtain wall assemblies are described in Figure 5.
The final seven options were then evaluated by the metric that is well known and
understood—annual energy use. The results
(Figure 6) were convincing in terms of the
contribution that daylighting would make to
energy savings and the performance of the
light redirecting glass. However, annual energy use did not make a clear case for any
one of the curtain wall options, except to
identify the worst performing (and least expensive) which had no thermal break in the
frame and the best performing (and most
expensive) option.
Since these options had developed in
large part due to concerns about occupant
thermal comfort, it made sense to try to
quantify the comfort performance of the
seven curtain wall assemblies. Comfort is a
much more difficult performance characteristic to quantify than energy use. Comfort is
most evident when it is absent; discomfort
causes complaints, reduced performance
and local or individual modifications to a
workspace such as sweaters, space heaters,
desk fans and aluminum foil over windows.
ASHRAE Standard 55 is the accepted standard for occupant thermal comfort in nonresidential buildings. Comfort is quantified
by a calculated Predicted Mean Vote (PMV),
an index that predicts the mean value of the
votes of a large group of people on a sevenpoint thermal sensation scale. Additionally,
the Predicted Percentage of Dissatisfied
(PPD) quantifies the percentage of thermally
dissatisfied people (ASHRAE 1992).
The analytical process developed to predict winter comfort conditions throughout
2000
South East (8)
West Corner (1)
South West (5)
North West (2)
North east (4)
South Corner (7)
East Corner (6)
5
1000
0
0
1
2
3
4
5
6
7
Month
8
9
10
11
12
Figure 3 - Typical floor cooling loads.
Figure 4 – Test cell of southeast façade mounted in artificial sky for tests. 1. Front Silvered Mirror 2. Redirecting
Film 3. Building façade mounted in the side of Artificial
Sky 4. Light Meter Array.
U-Values
2.50
2.00
1.50
Window-Assembly U-val
Frame U-val
Glass U-val
2.00
.50
0
Visionwall
Kawneer
7500 w/
1.25"
Alpen
Kawneer
7500 w/
VEI-2M
WW
Improved w/
1"
Alpen
WW
Improved w/
1.25"
Alpen
WW
Improved w/
VEI-2M
WW Standard w/
VEI-2M
Figure 5 - U-values of the seven curtain wall options.
Energy Use
71
71
69
68
67
KBTU/Sq Ft/Year
from the California Central Valley provide a
varied set of conditions and extremes for
building performance.
The initial runs, without lighting and mechanical systems, isolated and quantified
heating and cooling loads attributable to the
building envelope. Heating loads were relatively low, with the northeast and northwest
zones demonstrating the highest demand.
The southeast curtain wall developed the
highest cooling loads due to solar radiation.
The southwest façade benefited from some
site shading conditions and the other orientations were less challenged by solar exposure (Figure 3).
The overall annual cooling loads led the
design team to place a high priority on daylighting and shading in the curtain wall design. A series of DOE2.1e parametric simulations for each orientation were run, using
solar loads to compare and evaluate glazing
types and shading strategies: spectrally selective glazing versus standard, exterior
overhangs, interior light shelves, horizontal
louvers, mullion caps, canted glazing, etc.
Additional physical modeling using a mirrorbox artificial sky quantified the performance
of two types of light-redirecting glass: insulated glass with specular internal louvers for
the northwest clerestory glazing and lasercut prismatic glazing for the southeast
clerestories (Figure 4). By the end of
Schematic Design, the high performance
spectrally selective glazing with redirecting
clerestory glazing was selected. Shading devices for all orientations were designed to
optimize daylighting performance and minimize summer cooling loads.
With the cooling loads optimized, annual
energy use simulations were developed to
compare the performance of mechanical
system options. A chilled water system with
thermal storage was selected as it delivered
the least annual operational cost and required the least kWh.
66
65
No Okasolas Serraglaze
Okasolar Serraglaze Included
64
63
62
61
60
59
58
Visionwall
Kawneer
750 w/
1.25"
Alpen
WW
Improved
1.25"
Alpen
Kawneer
WW
Improved 750 w/
VEI-2M
w/ 1"
Alpen
WW
WWStandard
Improved w/VEI-2M
w/ VEI-2M
Figure 6 - Annual energy used of the seven curtain wall
options, with and without daylighting contributions and
light redirecting glazing.
ANALYTICAL PROCESS
Product Data
Weather Data
(San Francisco)
Window 5
LBNL
Glazing Performance
Building
Geometry
Therm
LBNL + Partners
Surface
Temperatures
Fishey
LOISOS +
UBBELOHDE
Mean
Radiant
Temp
DOE2
LBNL + Partners
UCB Comfort
UC BerkeleyASHRAE
Air Temp
Humidity
Air Motion
Metabolic Rate
Clothing
PMV - PPD
Radiant Asymmetry
Figure 7 - Analytical process used for thermal comfort
modeling of selected office bays.
Summer 2006 33
the office floors was simplified by selecting
five bays for simulation (NE corner, N, NW
corner, S and SE corner). For each of these
bays, the PMV and PPD was predicted for
each square foot of the office bay starting at
the window wall and moving 30 feet toward
the interior. The comfort calculation
methodology is described in Figure 7 (and in
greater detail in Ubbelohde Buildings IX).
Axonometric graphs were developed for
Figure 8 - PPD results for the
NE corner office bay with curtainwall option 1. The two horizontal scales represent distance
Figure 9 - PPD results for the NE
from the skin of the building and
corner office bay with curtainwall opthe vertical scale represents
tion 2. The two horizontal scales repPPD.
resent distance from the skin of the
building and the vertical scale represents PPD.
Figure 10 - Equal comfort graphic for best performing curtain wall option.
Figure 11 - Equal comfort graphic for selected (middle)
curtain wall option.
Figure 12 - Equal comfort graphic for worst performing
curtain wall option.
34 Journal of Building Enclosure Design
each curtain wall option and each bay (Figures 8 and 9). The degree of occupant dissatisfaction was reflected in the higher per
cent PPD (graphed on the vertical axis) and
the distance of dissatisfied occupants from
the curtain wall (horizontal axis). The graphs
quantified and compared the comfort performance of the curtain wall options in standard international comfort metrics and
made visible the effect of the curtain wall
temperature on occupant comfort.
There is no direct correlation between
PPD and the need for a perimeter heating
system and the design team still needed
some input on the issue of perimeter heat.
By analyzing the hours per year of occupant
discomfort with the best and middle performing curtain wall options, the annual energy use and cost of heat required in the
perimeter zone was quantified. The annual
levels of demand ($3,475 total annual heating costs for building perimeter zones for
the best option and $7,494 for the middle
option) enabled the owner to select individual radiant heaters rather than ducted
perimeter heat as the backup system if
there were occupant complaints.
In additional conversations with the
owner and design team a second strategy
was developed to comparatively describe
the comfort performance of the seven curtain wall options. A grid of mean radiant
temperatures moving from the curtain wall
back into the office bay was calculated for
each curtain wall option. A sectional drawing
of the office contained a desk located where
the MRT equals 71˚F to 72˚F for each option (Figures 10-12). For the best performing option, the desk was located at the window wall, but as the curtain wall options
allowed more thermal transfer, the desk
was moved away from the wall to indicate
locations of equal comfort. The description
of potential floor area lost to discomfort (as
much as 26,000 square feet with the unbroken frame option) was the most effective
means of communicating the relationship
between curtain wall performance and occupant thermal comfort. The owner selected the middle curtain wall of the seven
based on cost and occupant comfort.
CONCLUSION
While annual energy use is an important
metric for building and curtain wall performance, it cannot tell the whole story. Cooling
loads and daylighting are highly effective in
reducing annual energy costs for non-residential buildings but do not give a clear picture of the building performance during
cooler mornings and winter months, even in
a temperate climate like San Francisco. For
this office building, analytical methods and
descriptive techniques were developed by
the authors to describe the thermal comfort
implications of curtain wall design and specifications.
REFERENCES
• Abbaszadeh, S., L. Zagreus, D. Lehrer
and C. Huizenga, 2006. “Occupant Satisfaction with Indoor Environmental Quality
in Green Buildings.” forthcoming in
Healthy Buildings 2006, Lisbon, Portugal.
ASHRAE. 1992. Standard 55-1992R.
• BOMA What Tenants Want: 1999
Boma/Uli Office Tenant Survey Report.
Urban Land Institute, January 1999.
• California Code of Regulations. Nonresidential Compliance Manual For California’s
2005 Energy Efficiency Standards. Publication Number: CEC-400-2005-006-CMF
Published: April 2005 Effective Date: October 1, 2005. www.energy.ca.gov/title24
• Judith Heerwagen. “Do Green Buildings
Enhance the Well Being of Workers? Yes”.
Environment Design and Construction, 2000
• Huizenga, C. and Fountain, M. 1994-97.
UCB Thermal Comfort Program version
1.07
• Huizenga, C., L. Zagreus, E. Arens and D.
Lehrer. “Measuring Indoor Environmental
Quality: A Web-based Occupant Satisfaction Survey.” Proceedings, Greenbuild 2003,
Pittsburgh PA, November.
• Kats, G., Alevantis, L, Berman, A. et al.
The Costs and Financial Benefits of Green
Buildings. A Report to California’s Sustainable Building Task Force, October 2003.
• THERM.<http://windows.lbl.gov/software/therm/therm.html>
• Ubbelohde,S., Loisos, G. and Philip, S. “A
Case Study in Integrated Design: Modeling for High-Performance Façades”. Building IX Proceedings. Performance of Exterior Envelopes of Whole Buildings IX,
December 2004.
• US Green Building Council. 2003. LEED™
(Leadership in Energy and Environmental
Design) Reference Package for New Construction and Major Renovations. Version
2.1. WINDOW5.
• <http://windows.lbl.gov/software/window/window.html>
Feature
Window Comfort & Energy Codes
By Jim Larsen, Cardinal Glass
HEAT TRANSFER RATES THROUGH MOST windows are significantly greater than the adjacent insulated wall. This includes both
winter heat loss and obviously summer heat gain. Figure 1
demonstrates how quickly the roomside surface temperature of
glass can drop in response to cold weather.
It’s important to analyze window comfort implications before
settling on an energy strategy that may compromise the livability
of a space. As an example, take the situation of trading out “efficient” windows for an efficient furnace. On paper, the total energy consumption may look to be the same, but Figure 1 tells us
that the occupant will be exposed to cold windows during the
extreme weather.
COMFORT BASICS
Comfort can be evaluated with a statistical index called predicted percent dissatisfied (PPD)1. The calculation of PPD requires
a knowledge of room conditions (air temperature, air velocity,
humidity, and mean radiant temperature), and the occupant conditions (clothing level and metabolic rate). When comparing two
conditions, a lower PPD is desirable as this reduces the risk of
occupant discomfort.
Some common examples where cold weather PPD will be
improved (lower):
• Increase thermostat setting;
• Adding layers of clothing; and
• Increase level of physical activity.
During hot weather the converse of these will improve comfort as well as increasing air movement and/or reducing humidity.
of MRT varies with the occupant location relative to the window,
the size of the window and the room side surface temperatures
(typically taken as glass temperature). Figure 2 compares three
components of the MRT impact (size, proximity, and glass temp)
at 70°F inside/0°F outside to the change in PPD near the thermostat (no MRT shift).
Solar gains represent a high temperature radiant source that is
handled independently of the room/ambient MRT. From research
work performed by the Windows and Daylighting Group at
Lawrence Berkeley National Laboratory2, a correlation has been
developed that shifts the occupant comfort based on total solar
gain. Figure 3 shows this offset for two levels of solar radiation
and two levels of window solar gain.
The National Fenestration Rating Council (NFRC) has completed a research project3 that carries these comfort concepts
forward in much greater detail than presented here. Interested
WINDOW SPECIFIC INPUTS
Radiant conditions will be the primary driver on window comfort issues. Mean Radiant Temperature (MRT) expresses the occupant interaction with a window during cold weather. The value
Figure 1: Roomside Surface Temperature vs. Outdoor conditions
Figure 2: PPD vs. Window Conditions and Thermostat Settings
Figure 3: Solar Offset to Window Comfort
Summer 2006 37
readers are encouraged to follow the
reference listed for further background.
TABLE 1: EQUAL COMFORT FOR CHICAGO HOUSE
Low Solar Gain
Double Pane
Single Pane
Low-E
Clear
Clear
COMFORT VS. CODE: A REAL WORLD
Winter Thermostat Setting
70°F
72°F
73°F
EXAMPLE
In 2003, the Building America proSummer Thermostat Setting
78°F
74°F
73°F
gram supported the development of a
Energy Increase vs.
—
26%
50%
Habitat for Humanity duplex in the
Low Solar Gain Low E
Chicago area. This structure used envelope improvements, which included
low solar gain low-E windows, to
achieve an energy performance that is 37 per cent better than
boundaries for 32 per cent of the hours in a year. Compare this
the model energy code. The windows used in this project can be
to less than 10 per cent of the hours for the base case of low
represented by the line labeled as ‘Quad’ pane in Figure 1. The
solar gain windows.
winter design temperature in Chicago is about 0°F; reading up
The folly of the equipment for envelope trade-offs can be exthe quad pane line we see that the glass temperature will be aptended all the way to single pane windows. The combination of a
proximately 55°F at this design condition. Assuming this is adehigh efficiency furnace plus a high efficiency air-conditioner gets
quate comfort—we can now compare the comfort implications
the single pane windows back to an equal energy score, but the
from alternative energy strategies.
building space is now uncomfortable for 50 per cent of the hours
The same energy performance can be accomplished using orin the year!
dinary double pane windows along with a high efficiency furnace.
Faced with uncomfortable windows a homeowner can chose to:
The metrics listed below suggest, however, that these two struc1. Tough it out;
tures are very different.
2. Move away from the window;
1. Peak cooling loads increase by 18 per cent. This creates an
3. Leave the room;
extra burden for the electrical utility to generate sufficient
4. Add or remove clothing layers;
electricity reliability during hot weather periods.
5. Close the drapes and/or open the window; and
2. Carbon emissions increase by 12 per cent. The Midwest uses
6. Turn the thermostat setting to “comfort”.
mostly coal for electric generation.
Table 1 shows that in spite of paper “equivalence”, homeown3. There will be 989 hours in the winter when the double pane
ers could drive an energy increase approaching 50 per cent with
glass is colder than the 55°F benchmark for the original low
a simple vote of the thermostat adjustment.
solar gain low-E.
4. There will be 260 hours in the summer where, despite the
CONCLUSIONS
presence of air-conditioning, more than 30 per cent of the ocIn comparison to most elements in the building envelope,
cupants will be dissatisfied. This compares to 0 hours with the
windows are “first responders” to weather changes. Inefficient
low solar gain low-E glass.
windows will be cold in the winter and hot in the summer.
5. The house with double pane windows is at risk for solar overThe general populace would expect an energy efficient house
heat 760 hours during the swing season. This is not an energy
to be comfortable year round. If, as envelope designers, we allow
consumption measure, but indicates the level of involvement
paper trade-offs that fail the consumer comfort expectations,
needed by the home owner either through operation of
we’ve failed our professional responsibilities. More importantly
drapes/blinds or opening of the windows to vent excess heat.
these paper savings, given over to the control of a homeowner,
All told this “equivalent” structure will be outside the comfort
could destroy any semblance of a national energy policy and lead
to dramatic cost overruns and supply disruptions.
REFERENCES
1. ASHRAE 2005 Handbook of Fundamentals, Chapter 8; and
Standard 55-2004. http://www.ashrae.org
2. LBNL research paper available through ASHRAE via URL:
http://resourcecenter.ashrae.org/store/ashrae/newstore.cgi?ite
mid=7354&view=item&page=1&loginid=8813121&priority=none&words=window %20comfort&method=and&
3. NFRC comfort research: www.nfrc.org/documents/
UCBThermalComfortFinalReportFeb72006.pdf
4. Building America Habitat for Humanity duplex: www.eere.energy. gov/buildings/building_america/cfm/project.cfm/project=EEBA%202003%20HfH%20Duplex/state=IL/full=Illinois/city=Chicago
■
38 Journal of Building Enclosure Design
Feature
By Valerie L. Block and Tammy Amos,
DuPont Glass Laminating Solutions, Wilmington, DE
Laminated Glass, Providing
Security against Terrorist Attacks
PROTECTION AGAINST TERRORIST
ATTACKS IS now a common theme in the
design of government and commercial
properties. Americans witnessed terrorism
firsthand in 1995 with the bombing of the
Alfred P. Murrah Federal Building in Oklahoma City that resulted in the deaths of
168 men, women and children. Three
years later, two United States embassies in
East Africa were the targets of terrorist attacks that left 224 people dead and many
more injured. These two events, and others like it that have occurred around the
world, have led to a heightened awareness
of the need for greater security in both
government and commercial buildings.
DIFFERENCES IN GLASS BREAKAGE MAKE A
DIFFERENCE
Annealed glass is made by floating
molten glass over a bath of molten tin in a
furnace. The glass ribbon is gradually
cooled to room temperature through an
annealing process that also removes residual stresses that may have formed during
manufacturing. While there are many beneficial uses of annealed glass in buildings,
after an explosion, annealed glass breaks
into long, jagged shards that can cause serious injuries.
Tempered glass is a safety glazing material, according to the Consumer Product
Safety standard 16 CFR 1201. Tempered
glass is made by reheating annealed glass in
a furnace to approximately 1150 °F, which
is then rapidly cooled by flowing air uniformly onto both surfaces. The cooling
process locks the outer portion of the glass
in a state of compression and the central
core in tension. Although tempered glass is
considerably stronger than annealed glass,
it is not retained in its frame when breakage occurs. Instead the glass breaks into a
myriad of relatively small pieces of glass.
Laminated glass is often specified in
windows, doors and façades needing blast
protection because it provides impact
safety. The interlayer used to bond two or
more pieces of glass together provides
glass retention after a bomb has been exploded, and in doing so, minimizes the
chance of flying glass injuries to building
occupants or passersby. In addition, this
glass retention feature helps maintain the
integrity of the building envelope against
further vandalism after a terrorist attack
has occurred.
IMPACT RESISTANCE AND ENERGY SAVINGS
Glass retention is desirable in glazing
installed in seismic regions, as well as in
residential and commercial fenestration
intended for use in hurricane-prone areas.
Impact resistant glazing in properly designed frames keeps a home or building
intact during a severe weather event, protecting occupants and the structure itself
from collapse and interior water damage.
Window and curtain wall companies have
applied the knowledge gained from impact testing of hurricane products to the
development of products that offer bomb
blast protection.
Laminated glass not only contributes
to the overall performance of the window
by its ability to remain integral in its frame
if breakage should occur, but it can also
deliver acoustical benefits in terms of reducing outside noise. From an energy savings point of view, laminated glass can be
made with high performance glass and/or
coatings that result in a high visible light
transmittance and low solar heat gain coefficient.
While architects may specify laminated
glass for security, the cost justification can
often be measured in terms of energy savings expressed through lower utility bills.
APPLICABLE STANDARDS AND TESTS
ASTM F1642 Standard Test Method for
Glazing and Glazing Systems Subject to Airblast Loading (available at www.astm.org)
provides testing information for the glazing
or fenestration system in either a shock
tube or open-air environment. The
Windows in the Wilkie D. Ferguson, Jr. Federal Courthouse, Miami, Florida were made with laminated glass to
provide both hurricane impact and bomb blast protection.
Historic renovation included blast resistant windows at the
National Courts, Washington, D.C. Photo courtesy of
Masonry Arts.
standard also includes criteria for the classification of fragmentation. Currently, a specification to accompany the test method is
under development.
The ISC Security Design Criteria adopted by U.S. General Services Administration
in 2001 requires a balanced design of window systems to four specified levels. At the
minimum level, any glazing is acceptable. At
the medium level and high levels, the preferred glazing systems include tempered
glass with security film on the interior surface and attached to the frame, laminated
glass, or blast curtains. Monolithic annealed, heat strengthened and wired glasses are unacceptable glazing products.
Specifications for windows, skylights
and glazed doors are provided in the U.S.
Department of Defense Unified Facilities
Criteria (UFC) Minimum Anti-terrorism
Standards for Buildings. The UFC criteria
Summer 2006 39
references ASTM F2248 Standard Practice for Specifying an Equivalent 3-Second
Duration Design Load for Blast Resistant
Glazing Fabricated with Laminated Glass,
a static design methodology. Except for
retrofit applications, fragment retention
film is not considered a glazing alternative.
This year, the American Architectural
Manufacturers Association published
AAMA 510-06 Voluntary Guide Specification for Blast Hazard Mitigation for Fenestration Systems (available at www.aamanet.org). The document establishes
standard test sizes for fenestration system
evaluation and comparison.
THE DESIGN PROCESS
The design process may be different
from project to project. In some cases, an
experienced blast consultant will be required to conduct a vulnerability assessment
and recommend blast loading requirements
in terms of pressure and impulse, as well as
the acceptable level of performance for the
fenestration system. Blast consultants often
design programs to test proposed systems—at laboratories with shock tubes or
in an open-air arena setting.
40 Journal of Building Enclosure Design
The U.S. State Department now has
three standard designs for small, medium
and large embassy projects that are constructed on a design-build basis. Blast resistant exteriors are part of the master
plan for the security of these buildings.
Fenestration design for embassies has
been addressed by U.S. State Department
standards, which call for a higher level of
performance than other blast resistant
window and curtain wall systems. Special
attention has been given to attachments
and frame details of these systems. One
such system incorporates vertical and horizontal tubes or muntins that support the
laminated glass in the window. The system is designed to transfer the load from
the glazing to the structural muntins and
frame and ultimately to the adjacent structure (Valerie Block and David Rinehart,
“Security for U.S. Embassies,” Glass, June
2004, pp 67-68).
commercial building projects. Because
building codes in the United States represent minimum standards of construction,
it is unlikely that mandatory requirements
for security will be established any time
soon for commercial construction. As a
voluntary solution, building owners and insurance companies may be the pivotal
force in driving the adoption of security
glass solutions.
It is clear that designers are placing a
greater importance on the combined benefits of hurricane and seismic resistance,
bomb blast and forced entry protection,
and better acoustical and energy performance. Laminated glass installed in a properly designed fenestration system can deliver all of these benefits, but most
importantly, it can protect people inside
and outside of buildings from glass-related
injuries and the buildings themselves from
catastrophic collapse and damage.
■
TRENDS FOR THE FUTURE
As terrorist threats increase, the concern for building protection is expanding
from government buildings—courthouses,
military housing, and embassies—to
Valerie Block is a Senior Marketing Specialist
with DuPont™ Building Innovations™,
Wilmington, DE. Tammy Amos is a Marketing Specialist with DuPont™ Glass Laminating Solutions, Wilmington, DE.
Feature
How Does Fenestration Fit In?
Where have we been, where are
we now and where are we going?
By Barry G. Hardman, National Building Science Corporation;
James D. Katsaros, Ph. D., E. I. Dupont de Nemours and Company
A SIMPLE PURPOSE
Fenestration has one primary purpose
and that is to hold glass. This article first
reviews glass, then sash (that holds the
glass in the window frame), then problems with today’s fenestration installations, and finally a new forward-looking
concept currently under development—
an installation process that utilizes gravitywater management principles.
Glass has been an important building
material for millennia and, until 1960, glass
had very few changes. When the Pilkington brothers invented the float process
for glass manufacture, it opened up the
doors to a plethora of new and exciting
glass products.
Through 1960, glass was a fairly basic
material, which came in just a few colors
(clear, grey and bronze), which could be
made obscure by rolling a pattern on it
while it was still hot.
RECENT INNOVATIONS IN GLASS
In the past 40 years, glass manufacturing has become an extremely sophisticated industry that has developed glass that
can be used for energy savings, safety,
sound control, impact and blast resistance, photovoltaics, privacy (switchable
New glazings with spectrally selective low-E coatings can
reduce solar heat gain significantly with a minimal loss of
visible light (compared to older tints and films).
glass) and the list goes on. In the not too
distant future, electrochromic glazing will
contribute further energy optimization in
commercial buildings.
WINDOW FRAMES, SASH AND
INSTALLATION INSTRUCTIONS
At the turn of the last century craftsmen, carpenters and builders would build
their walls in such a manner as to include
the window frame. The craftsmen used
common wooden mill stock which was
designated by part numbers in the architect’s and mills’ catalogs, to integrate
window sills, jambs and head frames into
the building. They used proven water
management details, such as slopes,
shiplapping and drip chamfers.
Architectural detail books often gave
examples of good vs. faulty methods of integrating the frames (using the mill stock)
into the wall. Window sills, for example,
always ran well beyond the jambs and
were sloped, allowing water to freely run
off and be delivered to the outside of the
cladding. The tops of window frames
were also integrated with the cladding in a
shiplap fashion that guaranteed water was
drained to the exterior, using gravity.
Sealants were not available, thus frame integration into the wall relied on known
physics—simply stated, water likes to run
downhill.
SASH WAS INSTALLED LATER INTO THE
WINDOW FRAME
Around 1910, mill companies, which
also provided the mill stock to the craftsman, usually manufactured sashes (the
framework portion of the window that
holds the glass), which could be either
glazed or unglazed, and they were sold
separately to the builder to install into the
previously integrated window frame that
was part of the wall. Everybody used the
same sizes, mill stock and methods, therefore windows were uniform throughout
the industry, and sizing was based on available glass, which was sold by even twoinch increments.
PREASSEMBLED WINDOW UNITS—LOST
INSTALLATION PRINCIPLES
Early in the twentieth century, the
United States was well into the Industrial
Revolution and one of the innovations
from that entrepreneurial time was the
prefabrication of the window frame and
the sash as a whole unit. Thus, the window as we know it today was born.
Unfortunately, with that came the uncertainties of installing these pre-manufactured assemblies into the wall correctly
with procedures that allow for good
water management.
WINDOW AND INTERFACE LEAKAGE
DOCUMENTED
Most windows eventually leak. In particular, the window-wall interface often
leaks. That is why there was a need for a
national consensus installation standard.
Examine the abstracts for patents filed on
window systems over the last couple ofcenturies—they attempt to address an
ongoing problem—window leakage into
the wall cavity.
Summer 2006 41
Studies define water and air leakage
paths:
• June 1980, Air Leakage in Newly Installed Residential Windows: Lawrence
Berkeley Laboratory, University of California–Minnesota Energy Agency, John
Weidt, Jenny Weidt, Prepared for the
U.S. Department of Energy. Rate of Air
Leakage through Installed Exterior
Windows, Uninstalled, Windows and
Jobsite.
Conclusions: Manufacturers’ laboratorytested products always fell significantly
short of the rating when in the field. Purchasers of products rely on ratings for
product selection. Air Leakage is most
severe in corners, interlocks, and sills.
AAMA method of tabulating air leakage
(by crack-foot length) was deemed misleading.
Interface between window and wall:
“The air leakage performance of the
crack between the window unit and the
wall has a significant effect on the air
leakage performance of the entire window unit as installed.”
• Durability by Design guideline published by the Partnership of Advancing
Technology in Housing (PATH): “Most
leakage problems are related to improper or insufficient flashing details or the
absence of flashing.”
• Water Penetration Resistance of Windows–Study of Manufacturing, Building
Design, Installation and Maintenance
Factors, By RDH Engineering Ltd.,
Vancouver 12/31/2002. “… the dominant leakage paths of concern are those
associated with the window to wall interface, both through the window assembly
to the adjacent wall assembly and
through the window to wall interface
with the adjacent wall assembly.” The
study recommends redundant systems, sub-sill drainage for all windows.
• Journal of Light Construction, November 2003, based on CMHC / HPO
study: “35 per cent to 48 per cent of
newly installed windows were found to
leak through the window unit itself,
through joints between the window and
the rough opening, or both.”
“100 per cent of installed residential
windows examined after years in service
were found to leak either through the
window unit itself or at points of attachment to the building.”
42 Journal of Building Enclosure Design
NATIONAL CONSENSUS INSTALLATION
STANDARD: ASTM E 2112
Through 1995 there were no clear directions on how to install a window. In
1995 an ASTM committee was formed to
write the first fenestration installation
standard. The first edition was published
in 2001 and covered four basic methods
to integrate windows into the wall and
membrane to form a system. This document, known as E 2112 Standard Practice
for Installation of Exterior Windows, Doors
and Skylights, was developed with energy
in mind, as significant energy losses were
occurring due to the window-wall interface.
E 2112 is loaded with excellent information, however, its one major drawback
is that it assumes that windows don’t leak
in their joinery. Any leak in the joinery, unfortunately, would become trapped in the
wall cavity and be forced to the interior. It
is common knowledge today that windows will leak in their corners, if not immediately, then at some point after their
installation, when the weather-stripping,
vinyl, sealants and other components succumb to UV exposure, moisture and thermal expansion. That is not necessarily a
bad thing; it is not uncommon for the
complexity of this product. Therefore,
window manufacturers are acknowledging
that there is a distinct possibility of corner
leakage on their products sometime in the
life cycle of the product.
In 2001, the ASTM E 2112 committee
started working on the next iteration of
the document, which is being published
this year (E 2112-06). This document
recognizes the reality that there will be
joinery leakage and provides details and
methods to install a variety of sill pan
flashings under the window. Admittedly,
this is still just a recommended feature but
the majority of the committee hopes that
someday it will be required under windows where known joinery leakage occurs. The new standard also recognizes
self-adhered flashing.
Why is that so revolutionary? Well, up
until eight months ago there was no credible standard for determining the serviceability or durability of self-adhered flashings. There was no in-service track record
of continued performance during their
service life. In reality, eight months ago,
duct tape or even masking tape would
have been allowed to be used as “flashing”, as there were no standards. In 2005
AAMA came to the rescue with AAMA
711 Self Adhering Flashing standard. While
the standard is still far from complete, for
the first time it establishes criteria to be
able to compare one product against another for a particular application.
INNOVATIVE BUILDING MATERIALS ADD TO
COMPLEXITY OF INSTALLATION
The struggle which began early in the
twentieth century continues today, even
though we have developed a national installation standard and have sealants,
membranes, weather-stripping, gasketing,
and the list goes on. The fact is, every innovation seems to have added more complexity to the installation. And the struggle
continues.
REALITY CHECK—REMOVAL AND
REPLACEMENT
What do roofs, water heaters and windows have in common? They all leak
eventually and have to be replaced. They
all have a limited lifespan which is less
than that of the building. More energy-efficient versions are made available continuously.
It is reasonable to assume that you will
have to change your water heater in ten
years so it has been installed in a manner
that makes it fairly simple to remove. The
roof has a predictable life as well and so
replacement is easily accomplished. Best
of all, for both the roof and the water
heater, the removal is non-destructive to
the rest of the building.
Now the window installation, by comparison, is bizarre. They are installed and
embedded in the wall so deeply that only
destructive technology can be used to remove their deeply ensconced roots. They
are glued, screwed, nailed, covered with
membranes and cladding on the outside
and then embedded by gypsum, plaster,
paint, finish, stools and aprons, just to
mention a few, on the inside. Why in the
world do we install windows so deeply
among the layers of the wall, that you literally cannot get it out without destroying
the wall?
CODES AND CHANGES
In spite of the integration of all building
code bodies into the International Code
Council (ICC), one might expect that
code would require quality window installation. Factually, there is very little in the
code that deals with installation of fenestration and its flashing. In the past several
code cycles a little language is starting to
creep in, which primarily requires manufacturers to supply installation instructions
to the builder at the time of delivery of
the product.
Which manufacturers, you may ask—
windows, membranes, sealants, flashings?
Who knows? The codes have embraced
membranes to be installed on the exterior
of the building, which is starting to come
into effect now. Strangely, codes do not
define flashing. The new version of E 2112
clearly defines flashings and how they are
used.
MODULAR INSERT FENESTRATION SYSTEM:
A NEW-OLD CONCEPT FOR INSTALLATION
Consider a forward-looking concept
where the builder is given a seamless,
molded, robust receptor that is specially
designed to marry with all standard windows and is based on standard sizes. Simplistically, this is a four-sided pan system
which is molded and has no joints to leak.
It integrates with the building’s water-resistive membranes and forces drainage to
the outside of the cladding—just like the
old master builders and architects knew,
previous to the innovation of the preassembled window unit.
This new system does not rely on the
water being evacuated via the membranes
in the wall cavity, but rather, diverts it immediately to the exterior of the cladding.
Think of the benefit to the builder. He will
be able to put the receptor in at any time
when building the walls. This installation
would then allow for a later window installation without penetration of claddings or membranes.
The builder would then be
able to finish the walls, add
cladding, sheetrock, paint, clean
the cladding—without the windows being in place. At a point
when the builder felt it best to install the windows, he would
come by and snap them into the
receptors. Window manufacturers interviewed endorse the concept, as it will enhance the ability
of the window to shed water to
the outside, keep them clean and free of
scratches during construction of the building and allow more flexibility for delivery.
It will also keep them from being banged
around on the job or stolen. The performance of the installed window would
not be dependent on the skill and training,
or lack thereof, of the installer. Current
building practices have many different
trades working around the fenestration
openings, but the lack of coordination
among them creates the difficulty with interface.
PLANNED OBSOLESCENCE OF WINDOWS
• Windows are the single largest contributor to energy loss in the exterior
walls.
• This loss translates to high energy bills
and loss of comfort.
• Cost of energy can be assumed to rise
constantly and substantially over the
lifetime of the building.
• Allow for innovative technologies without prohibitive expenses and disruption.
• The service life of a window is far less
than the wall. It has to be replaced two
to four times over the life of the building.
• The labor cost to remove and replace
windows and to repair the surrounding
walls, interior and exterior, exceeds
the cost of the window.
Another important feature of the receptor system and methodology is that it
will make for simple replacement of the
window. Why is that important? Because
window technology is moving ahead in
strides—self-cleaning glass, energy-efficient glass, photovoltaics, acoustical windows, impact-and blast-resistant glass and
window systems. The list goes on. Without a doubt, manufacturers can agree that
glass will continue to become more and
more sophisticated, bringing more and
more energy-saving concepts and comfort
to the inhabitants of the building. The current destructive removal methods deter
building owners from adopting innovative
new window technologies sooner.
RECENT TESTING OF PROTOTYPES
Prototype receptor systems were installed in conjunction with two different
EIFS systems. Specimen one used a liquidapplied water-resistive barrier (LWRB)
over the substrate. Modular Insert Fenestration Systems (MIFS) product was installed on top of the LWRB. Additional
LWRB was then applied over the MIFS installation flange with fiberglass netting.
With specimen two, the MIFS frame
was installed onto the substrate, then
LWRB was applied over the substrate and
over the MIFS attachment flange. Both
specimens then had 1-1/2” Styrofoam installed, which was further coated with a
1.5 mm cementitious acrylic coating.
• ASTM E 330 Test Method for Evaluation of Structural Performance—
The combined wall and fenestration
products achieved a 45 psf positive and
negative using a fenestration product
that was rated at 25 psf.
• ASTM E 331 Test Method for Static Water Penetration—The combined wall and fenestration products
achieved 12 psf for 15 minutes.
• ASTM E 283 Air Infiltration—Both
combined wall/fenestration products
measured 0.03 cfm per square foot
(54 sq. ft. samples) at1.57 lb/ft2.
CONCLUSIONS
There are manufacturers now developing this concept. Changes are expected
in window installations that are based on
traditional gravity-based water management principles. The receptor approach
requires the receptor to be built into the
wall, is designed in such a way that the
window can be simply snapped into the
receptor without piercing the receptor or
the cladding or the membranes. Even if
the joinery at the corners of the windows
leaked, it would not make any difference,
because that leakage would be diverted to
the outside of the cladding.
■
Summer 2006 43
Industry Update
Tax Credits Made Easy by
Choosing ENERGY STAR®
By Rich Karney,
U.S. Department of Energy
THE U.S. DEPARTMENT OF ENERGY
(DOE) and its fenestration partners were
pleased with guidance issued by the Internal
Revenue Service (IRS) earlier this year that
recognized the value of the ENERGY
STAR® label for windows. It is now easy to
take advantage of Federal tax credits for
windows by choosing ENERGY STAR®.
The Energy Policy Act of 2005 introduced tax credits for building envelope
components that meet minimum requirements of the 2000 International Energy
Conservation Code (IECC) with supplements, or other applicable requirements.
The legislation granted credits of 10 per
cent of the cost of eligible improvements,
not to exceed $500 ($200 for windows)
over the length of the program—the 2006
and 2007 tax years. Once the bill was
passed and signed, ENERGY STAR® and
energy-efficiency professionals looked to
the IRS for guidance on how the credits
would be implemented.
In February of this year the IRS issued
notice 2006-26, which outlined the specific
requirements for eligible building envelope
components and provided guidance on how
eligibility was to be confirmed and documented. Notable provisions of the notice
included an expansion of all references to
the 2000 IECC, guidance for issuing and
using a Manufacturer Certification Statement, and a special rule for ENERGY
STAR® windows and skylights.
The IRS effectively simplified many eligibility requirements by expanding references
to the 2000 IECC, to also include the 2004
Supplement to the 2003 IECC. This means
that eligible envelope components may
qualify for tax credits by meeting the requirements of the 2001 or 2004 Supplements to the IECC. The expansion allows
products to qualify for the credit by meeting the simpler, but equally stringent, requirements of the 2004 Supplement.
The IRS also addressed questions about
consumers being burdened with determining and documenting compliance with the
IECC by introducing protocols for manufacturer certification statements. A manufacturer of an eligible product may certify to a
taxpayer that the component qualifies for
the tax credit in a certification statement
provided with the product. In turn, a consumer may rely on a manufacturer’s certification that a product is eligible when claiming the tax credit. Taxpayers will not need
to submit the certification statement with
their tax documents, but should retain the
statement for their own records.
A manufacturer of an eligible
product may certify to a taxpayer
that the component qualifies for the
tax credit in a certification statement
provided with the product.
The greatest simplification for consumers came from a special rule that IRS issued for ENERGY STAR® windows and
skylights. Recognizing that ENERGY STAR®
qualified windows and skylights exceed
IECC requirements nearly everywhere in
the U.S., the IRS treats all ENERGY STAR®
qualified windows and skylights as eligible
products and allows consumers to rely on
the ENERGY STAR® label, rather than a
manufacturer’s certification statement,
when determining if the product qualifies
for the credit. As with the certification
statement, a taxpayer does not need to
submit the ENERGY STAR® label to the
IRS, but should keep it for their records.
Unfortunately, the special rule does not
apply to ENERGY STAR® qualified doors,
even though they also will nearly always exceed IECC requirements. DOE has encouraged all ENERGY STAR® manufacturing
partners to provide certification statements
with qualified doors and advises consumers
to look for doors with these statements to
ensure eligibility for the tax credit.
The IRS guidance also covered products
other than windows, doors, and skylights.
Insulation materials or systems, metal roofs,
and storm windows and doors are also eligible for the same $500 tax credit. Insulation materials must be primarily designed to
reduce heat loss or gain, and metal roofs
must meet or exceed ENERGY STAR® requirements in order to be eligible for the
credit. Storm windows and doors are eligible if they meet IECC requirements when
installed in combination with existing windows and doors.
Additional incentives exist for energy-efficient fenestration and building envelope
components through builder tax credits for
energy efficient homes. The Energy Policy
Act introduced a $2000 credit for new
homes that have annual HVAC energy consumption that is 50 per cent less that that of
a home constructed according to the 2003
IECC, 1/5 of which must be associated with
building envelope components. A $1000
credit is also available for manufactured
new homes with annual HVAC consumption of 30 per cent less than a home constructed to the 2003 IECC. IRS notice
2006-27 defined eligible homes as those
verified by a RESNET (or equivalent rating
network) accredited certifier to meet the
requirements prescribed in the legislation.
The department looks forward to these
credits advancing the market for energy-efficient building products. In addition to
other financial incentives and energy benefits, federal tax credits are another asset for
individuals and organizations that seek to
market quality, energy-efficient products.
For more information on these and
other tax incentives, visit the ENERGY
STAR® website at www.energystar.
gov/taxcredits.
■
Summer 2006 45
Industry Update
By James C. Benney, NFRC Executive Director
NFRC Standards, Codes and
Fenestration Research Activities
INTRODUCTION
The National Fenestration Rating Council
(NFRC) is a nonprofit (501(c)3) organization
whose mission is to develop and administer
comparative energy and related rating programs that serve the public and satisfy the
needs of its private sector partners by providing fair, accurate and credible, user-friendly information on fenestration product performance. NFRC develops and publishes standards
(see descriptions below) and administers a
certification and labeling program to ensure
accurate, uniform and credible energy performance ratings for all fenestration products;
including windows, doors, skylights, curtain
walls and storefront systems.
TECHNICAL STANDARDS AND CODES
NFRC standards are referenced in the International Energy Conservation Code
(IECC), the International Building Code (IBC)
and the International Residential Code (IRC);
as well as ASHRAE 90.1 and 90.2; and many
state and local energy codes, such as California’s Title 24. All NFRC standards are available
at no charge on its website (www.nfrc.org).
IECC REFERENCE
IECC 102.5.2 Fenestration product rating, certification and labeling
• U-factors of fenestration products shall be
determined in accordance with NFRC 100
by an accredited, independent laboratory,
and labeled and certified by the manufacturer.
• The solar heat gain coefficient (SHGC) of
glazed fenestration products shall be determined in accordance with NFRC 200 by
an accredited, independent laboratory, and
labeled and certified by the manufacturer.
NFRC STANDARDS
• NFRC 100 (2004) “Procedure for Determining Fenestration Product U-factors”.
• NFRC 200 (2004) “Procedure for Determining Fenestration Product Solar Heat
Gain Coefficient and Visible Transmittance
at Normal Incidence.”
46 Journal of Building Enclosure Design
• NFRC 400 (2004) “Procedure for Determining Fenestration Product Air Leakage.”
• NFRC 500 (2004) “Procedure for Determining Fenestration Product Condensation Resistance Values.”
NFRC CERTIFIED PRODUCTS DIRECTORY
NFRC administers a voluntary certification
and labeling program that provides assurance
to architects, specifiers and code officials that
fenestration products have been rated in accordance with NFRC procedures and by an
independent, accredited lab.
Those products that have been authorized for certification and manufacturers that
have been licensed by NFRC are listed in the
Certified Products Database. This database
lists the ratings and attributes of hundreds of
thousands of fenestration products and systems and is freely available on the NFRC
website (www.nfrc.org).
RESEARCH ACTIVITIES
In addition, to these Programs, this nonprofit organization also spends a considerable
amount of time, energy and money approving
and funding fenestration product research.
Since 2004, the NFRC Board of Directors has
approved over $500,000 to fund research
projects that serve its mission. Typically, research projects are related to improving the
accuracy and dependability of its rating programs (including the basic science used in
computer programs that model heat transfer
mechanisms) or to develop new rating programs such as Thermal Comfort (see below).
The following is a list of projects that have
been recently completed or are in process of
completion:
• Effects of Surface Heat Transfer Coefficients on U-factor for projecting and highly conductive products;
• Investigation of Heat Transfer Effects of
Sloped and Ventilated Internal Cavities of
Framing Systems;
• Study of 3D corner heat transfer effects in
fenestration products;
• Development of a procedure (and model)
for the U-factor rating of domed skylights;
• Development of a procedure (and model)
for SHGC and VT ratings of domed skylights;
• Development of U-factor ratings for tubular daylight devices; and
• Development of a thermal comfort rating.
In addition, there are number of proposed
research projects awaiting approval, including:
• VT ratings for non-specular glazings; and
• Research to support grouping rules and
Condensation Resistance ratings for the
Component Modeling Program.
THERMAL COMFORT RATINGS
Many NFRC members and stakeholders
believe that thermal comfort is a missing component in our current rating system. There is
a definite relationship between energy efficiency and comfort; and between comfort
and productivity and personal satisfaction.
Higher fenestration U-factor ratings tend to
indicate colder interior window surface temperatures in the winter; leading to higher levels of discomfort and/or levels of dissatisfaction. The same can be true in terms of solar
heat gain in the summer; where high levels of
solar gain increases the interior surface temperatures of fenestration products to uncomfortable levels. These levels of dissatisfaction
or discomfort depend upon a complex series
of factors including the time of day, location,
orientation, exposure, and distance from the
window. The research being conducted is intended to assist NFRC in developing a Thermal Comfort Rating; which should providing
additional information about fenestration performance to architects, specifiers and homebuilders.
For more information about this program,
or any of the on-going research projects at
NFRC, please see our website at www.
nfrc.org or contact our office in Silver Spring,
Maryland at 301-589-1776. NFRC is also an
AIA accredited information provider and offers courses to those firms interested in learning more about fenestration performance. ■
Industry Update
BEC Corner
BOSTON-BEC
By Richard Keleher
Boston’s BEC has been getting 25 to
30 attendees each month. We have begun
a program of outreach to the larger offices in Boston and environs to improve
attendance. Our co-chair, Maria Mulligan,
is back after an extended maternity leave
and she is beginning to work on improving the quality of our monthly presentations. Presentations of note that we have
had are; Mineral fiber cavity insulation by
Dr. John Straube, ABAA adhered sheet air
barrier specifications by Mark Kalin,
Through-Wall Flashings by Len Anastasi,
and Rainscreen Cladding Systems by our
chairman, Richard Keleher. We also had
our first ever “roadshow,” where three
experts from the BEC went out to the
surrounding region and presented a sequence of three two-hour sessions on
building science (heat, air, moisture), the
management of liquid water and specifying the building enclosure. For more information on our presentations, projects,
membership and contacts, tour our website, www.bec-boston.org.
CHARLESTON-BEC
By Nina Fair
Building Enclosure Council-Charleston, had its initial organizational meeting in October, 2005. Regular meetings
started in January, 2006. BEC-Charleston
has generated a lot of interest and excitement in the design and construction communities. Our recent and planned programs are:
• February 2006 Meeting
Topic: ASTM E 2112 Standard for
Window Installation with Proper
Flashing
Presenter: Mr. Barry Hardman with
National Building Science Corporation
• March 2006 Meeting
Topic: Metal Wall Rainscreen &
Moisture Control
•
•
•
•
Presenter: Mr. Andrew Laiewski with
Centria Architectural Systems
April 2006 Meeting
Topic: ASHRAE 90.1 Energy Code
Envelope Compliance
Presenter: Mr. Dennis Knight, P.E. of
Liollio Architecture
May 2006 Meeting (Joint meeting
with ASHRAE Charleston)
Topic: Cool Roofs
Presenter: Dr. William Miller of Oak
Ridge National Laboratory
June 2006 Meeting:
Topic: “Flashing: The Good, the Bad
and the Ugly”
Program: Hands-on exploration of
flashing materials, details and related
issues
August 2006 Meeting: Thursday,
August 24, 6:00 – 7:30 PM
Topic: NFRC Certification and
Programs
Presenter: Bipin Shah, Director of
Programs, National Fenestration
Rating Council (NFRC)
COLORADO-BEC
By Ned Kirschbaum
BEC-Colorado’s inaugural meeting
was on August 10, 2005 and we have met
on the first Wednesday of each month
since then. Attendance has consistently
been between 15 and 25 participants including architects, engineers, contractors,
subcontractors and suppliers. Presentations have included a computation fluid
dynamics case study, detailing of windows
in brick veneer walls, the ins and outs of
horizontal waterproofing systems, a roofing systems overview, snow country roof
design: materials, assemblies, and moisture management, fluid applied air barriers, building science principles in cold and
very cold climates, weather-resistive barriers, and best (and worst) practices for
exterior stucco in Colorado.
In the future we hope to jointly host,
with the University of Colorado and
BETEC, a one day building science seminar. We are also planning to create a halfday seminar on building envelope design
in very cold, snowy climates, given by
local BEC members.
DC-BEC
By Tim Taylor
The inaugural meeting of the DC-BEC
occurred in February of 2005 at the
Washington DC offices of Gensler. Since
then, the DC-BEC has hosted approximately a dozen meetings on selected aspects of building enclosure design. Topics
have included basic design criteria for curtain walls, including wind, water and air,
shadow box design guidelines, fundamental architectural design considerations for
existing and new blast resistant building
envelopes, firestop design of spandrels,
building envelope thermal testing, the
new NIBS Building Envelope Design Guide,
building structural deflections and exterior
cladding, selecting roofing systems for
long term performance, the what, when,
where, why and how of air barrier design,
carbon fiber reinforcement of precast
concrete panel cladding. Future topics for
the fall include exterior wall maintenance
systems design, the National Fenestration
Rating Council’s latest rating system and
water management within exterior walls.
Our meetings are an hour long, are held
at 4 pm on the first Wednesday of each
month except in July, August and December, when we suspend the meetings in observance of vacations and end of the year
parties. They are attended by facilities
owners, developers, architects, exterior
wall consultants, exterior wall cladding
subcontractors, and manufacturer representatives.
Attendance is free and those who attend can earn a continuing education unit
which is automatically reported by filling
out a sign-up sheet.
To contact the BECs, go to www.bec-national.org/boardchairs.html
Summer 2006 47
BEC Corner
HOUSTON-BEC
By Andy MacPhillimy
AIA Houston is joining the national initiative by AIA National and the National
Institute for Building Sciences by establishing BEC-Houston, an open forum to promote discussion, education and the transfer of information and technology among
all stakeholders in buildings enclosures—
owners, architects, engineers, consultants,
manufacturers, installers, contractors and
others. We are excited about this opportunity to raise regional expertise, skill and
the understanding of building exterior enclosure construction, resulting in the improvement of the quality of design, the installation and the maintenance. A kick-off
meeting was held on May 24th and was attended by a diverse group of those interested in the mission of BEC-Houston.
In the coming weeks we will be
establishing the steering committee to set
the vision and mission of BEC Houston
and the program committee to develop
the series of speakers, panels and work
shops needed to accomplish the vision and
48 Journal of Building Enclosure Design
mission established by the steering committee.
MINNESOTA-BEC
By Judd Peterson
From our inception on February 14,
2006, the BEC-Minnesota has scheduled
monthly meetings involving both lectures
by experts about specific aspects of the
building envelope, and informal round table
discussions about preferred section detailing of the building envelope. Speakers have
included Kim Bartz of WR Grace Company
and Brent Anderson of BA Associates
about air/water/vapor barriers on backup
construction and sheathing; Dan Braun and
Dan Johnson of Architectural Testing, Inc.
about the range of possible field tests for
exterior building envelopes; Craig Hall of
WL Hall and Wausau Windows about critical detailing of window and curtainwall
openings and primary seals.
Upcoming lectures include Bob Moran,
Northeast Regional Technical Representative of BASF Polyurethane Foam Enterprises, talking on Spray Polyurethane Foam In-
sulating Air Barriers in the exterior envelope; Chemrex Technical representatives
will discuss all aspects of sealant application, including chemical compositions,
compatibilities, incompatibilities, proper
uses depending on the type of sealant,
primers, application conditions; and Craig
Thompson, Technical Representative of
the Copper Development Association,
talking on copper sheet metal enclosures
and detailing, with examples formed and
fabricated at the seminar by McGrath
Sheet Metal.
Our BEC participants have voiced appreciation for the access to critical building
enclosure expertise, and the extended resources and advice from other BEC peers.
PORTLAND-BEC
By Rob Kistler
In the short period since the introductory meeting held in December 2005, the
Portland-BEC has developed into a well
attended monthly seminar hosted at various architect and contractor offices.
Consisting of roughly equal numbers of
manufacturing representatives, contractors and architects, the seminars have attracted between 30 and 45 people. The
topics, presented by local and national experts, have alternated between the theoretical and the practical. Seminar topics
range from Portland cement plaster, and
air and moisture infiltration and barriers,
to seminars on barrier compatibility with
sealants, and envelope acoustics. Adding
interest to each seminar, a “detail of the
month” that is relative to the topic is displayed and discussed prior to the presentation. The “BEC Programming Group,”
which is responsible for developing the
programs and lining up speakers is also
working towards producing a two-day
seminar to take place in November 2006.
Interested parties can find out more in formation at www.aiaportland.com/ (Member
resources) (Committees).
utes of business and an hour+ program.
Programs are diverse and have included a
window testing demonstration, discussion
of the Washington State Condominium Act
relating to building envelope, air barriers,
curtain walls, sealants, and structural
forensic investigation practices to name a
few.
We have two committees in place, one
for education/programming and another to
help define third-party building envelope
inspectors as allowed for by the Condo-
minium Act. We also have a web site
under construction, www.seabec.org and
are sponsoring a golf tournament in the
fall. Our goals for the future are to educate
contractors, help the local AIA chapter
with building envelope seminars and workshops, forge ties with the University of
Washington Architecture and Building
Construction programs, collaborate with
BEC Portland and continue operating as a
respected forum for discussion and learning of building envelope issues.
■
SEATTLE-BEC
By Dave Bates
The Seattle Building Enclosure Council
or SeaBEC as we call it, is almost halfway
through its second year and it has been a
good adventure so far. We have a governing board of six with diverse backgrounds;
contractor, owner’s rep, architect, product rep, building envelope consultant and
an architectural consultant with the NW
Wall and Ceiling Bureau. Our membership
is more diverse with students, developers,
contractors, architects, engineers, envelope consultants, construction defect attorneys, building department personnel,
product reps and industrial hygienists. We
meet the third Thursday of every month,
from 5-7pm with the exception of July and
August. The Board meets once a month
year-round. Our membership base is currently at 110 members and we have had
anywhere from 35 to 82 people attend
our monthly meetings.
Our membership fees cover the cost of
our meeting rooms, air fare and lodging
for our chair to attend the national BEC
and BETEC meetings and necessary operational expenses such as our annual audit.
We charge 50 dollars for a single membership with student memberships gratis.
Member firms and product reps sponsor
refreshments at our meetings which typically include sandwiches. Meetings consist
of 1/2 hour networking session, 15 minSummer 2006 49
Buyer’s Guide
AIR BARRIERS
Dupont Building . . . . . . . . . . . . . . . . . . . . . . .7
ELASTOMERIC ROOF COATINGS
ROHM & HAAS . . . . . . . . . . . . . . . . . . . . . .35
AIR AND VAPOR BARRIERS
Carlisle Coating &
Waterproofing . . . . . . . . .outside back cover
ENGINEERS
Sutton-Kennerly & Associates Inc. . . . . . . . .30
ARCHITECTS
HKS Inc. . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
EXTERIOR INSULATING FINISH SYSTEMS
ROHM & HAAS . . . . . . . . . . . . . . . . . . . . . .35
MANUFACTURER REFLECTIVE ROOF
COATING • LEED COMPLIANT
Karnak Corporation . . . . . . . . . . . . . . . . . . .18
MASONRY
Mortar Net USA Ltd. . . . . . . . . . . . . . . . . . .15
FENESTRATION CONSULTANT
National Building Science Corporation . . . . .38
METAL ROOF COATINGS
ROHM & HAAS . . . . . . . . . . . . . . . . . . . . . .35
BUILDING DESIGN SERVICES
Wauters Design GPP LLC . . . . . . . . . . . . . . .30
FLUID APPLIED AIR & MOISTURE
BARRIERS
Prosoco Inc. . . . . . . . . . . . . . . . . . . . . . . . . .13
MULTI-DIRECTIONAL DRAINAGE
BARRIER
Valeron Strength Films . . . . . . . . . . . . . . . . .36
BUILDING ENVELOPE ARCHITECTS
Conley Design Group Inc. . . . . . . . . . . . . . .17
GLASS & GLAZING
Cardinal Glass . . . . . . . . . . . . . . . . . . . . . . . . .9
BUILDING PRODUCTS
Georgia Pacific . . . . . . . . . . .inside front cover
GLASS COATINGS
AFG Glass . . . . . . . . . . . . . . .inside back cover
BUILDINGS SCIENCE & RESTORATION
CONSULTANTS
Read Jones Christoffersen . . . . . . . . . . . . . .48
GLASS FABRICATIONS
AFG Glass . . . . . . . . . . . . . . .inside back cover
ASSOCIATION
National Fenestration Rating Council . . . . . .25
CERAMIC TILE ADHESIVES
ROHM & HAAS . . . . . . . . . . . . . . . . . . . . . .35
CONCRETE MODIFIERS & SEALERS
ROHM & HAAS . . . . . . . . . . . . . . . . . . . . . .35
CONCRETE ROOF TILES, MODIFIERS &
SEALERS
ROHM & HAAS . . . . . . . . . . . . . . . . . . . . . .35
CONSULTANTS
Patenaude-Trempe Inc. . . . . . . . . . . . . . . . . .50
50 Journal of Building Enclosure Design
GLASS MANUFACTURING
AFG Glass . . . . . . . . . . . . . . .inside back cover
INSULATING GLASS
AFG Glass . . . . . . . . . . . . . . .inside back cover
INSULATION
Knauf Insulation . . . . . . . . . . . . . . . . . . . . . . .3
INSULATION MANUFACTURER
Johns Manville . . . . . . . . . . . . . . . . . . . . . . . .44
MEMBRANE/VAPOR BARRIER
CertainTeed . . . . . . . . . . . . . . . . . . . . . . . . .31
ROOF DECKS
Global Dec-K-ING . . . . . . . . . . . . . . . . . . . .49
ROOF DECKS & BALCONIES/
WATER PROOFING & ROOFING
Skyline Building Systems Inc. . . . . . . . . . . . .22
ROOFING MANUFACTURER
GAF Materials . . . . . . . . . . . . . . . . . . . . . . . . .4
SIDING, WOOD, VINYL FIBER CEMENT
ROHM & HAAS . . . . . . . . . . . . . . . . . . . . . .35
WATER PROOFING
CETCO Building Materials Group . . . . . . . .40
WATERPROOFING, RESTORATION
The Waterproofing Company Inc. . . . . . . . .13