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 2007
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Contents
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PUBLISHER & DIRECTOR OF SALES
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ADVERTISING DESIGN
James Robinson
LAYOUT & DESIGN
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©2007 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.
Features:
10
Evaluating Energy Efficiency
Using Whole-Building
Simulation Tools
16
20
24
29
33
ASTM C 652 Bricks: Less is
Good
Transitions: How to Design
Facade Interfaces
Reflections on the Window
Wall
Air Barriers: Walls Meet
Roofs
24
Curtain Wall Mock-up
Testing
Window Walls
36
39
41
Curtain Wall
Testing
Perimeter Joints
Rain Screens: The New
Standard
Characterizing Air Leakage in
Large Buildings: Part I
Air
Leakage
JBED
33
41
Messages:
07
08
Message from NIBS President, David A. Harris
Message from BETEC Chairman, Wagdy Anis
Industry Updates:
46
50
BEC Corner
NIBS Application
50
48
BETEC Application
Buyer’s Guide
On the cover: New York
city’s Chrysler Building is
known for its art deco crown.
Learn more about distinctive
characteristics of exterior walls
in Henry Taylor’s article on
page 33.
Summer 2007 5
Message from NIBS
David A. Harris, FAIA
THE GREEN BUILDING MOVEMENT has
always been with us. If it hasn’t, it should
have been. Energy conscious design, minimizing waste, recycling, using renewable
resources and the like should be integral to
the design and construction of all buildings.
Today, we’re bombarded with invitations to conferences focusing on building
green and green buildings. To me, it makes
more sense for us to focus our energies on
improving the full range of building performance—security, safety, appearance,
durability and functionality—to name just a
few. Each of these performance needs
competes with the others for its share of
space during design, for dollars during construction and for other resources over a
building’s life cycle. Design professionals,
constructors and building owners must
properly balance these needs and costs.
We can get rating points for using sustainable materials such as recycled wallboard, non-VOC emitting carpet and ceiling
tile, and increased insulation in the building
envelope. But if we don’t look at total building performance, all of our “green” efforts
may be for naught. If the building is in a hurricane zone and we haven’t provided adequate tie-downs for the rooftop equipment,
much of that equipment can be blown
away, opening the roof system to hurricane
levels of rain, which will soak the insulation,
saturate the drywall, ceiling tile and carpet,
leaving the interiors in ruins. What have you
accomplished?
The Journal of Building Enclosure Design
(JBED) brings the design professional’s attention to whole building performance.
Look beyond the low hanging fruit of
sustainability to the high performance building concept. The U.S. Congress deserves
strong praise for its foresight and wisdom in
establishing the high-performance buildings
program to create high performance goals
and accompanying metrics for public and
private buildings of the future.
The building envelope is a large and important portion of the building. Improved
envelope performance will improve buildings and systems life spans, building operation and maintenance, occupant productivity, safety and security, as well as mission and
systems performance. JBED and the
BETEC’s focus will continue to be the improvement of the building envelope for
greener, sustainable and high performance
buildings.
Please send us your comments and suggestions for additional topics for JBED. And,
in the interest of recycling, please pass this
issue along to a colleague.
David A. Harris, FAIA
President
National Institute of Building Sciences
Summer 2007 7
Message from BETEC
WELCOME TO THE SUMMER
2007 edition of the Journal of Building
Enclosure Design (JBED)!
This edition is a tribute to the
Building Enclosure Councils (BECs)
of the U.S., all eighteen of them
(www.bec-national. org/boardchairs.html) and their cousins and
predecessors in Canada. The BECs,
a partnership between the AIA and
the National Institute of Building SciWagdy Anis, FAIA, LEED AP
ences, are truly an untapped force
that is discovering its potential in the
influence it can have on the design, construction, product development and advancement of a unique and rapidly developing
rollercoaster of focus on how buildings perform in their environments, in all of the eight climate zones of North America.
With a new national focus on energy efficiency, the carbon
footprint of buildings and their contribution to climate change,
this represents a unique time in the history of North America to
make an impact, and they are truly taking this to heart. The BECs
are working as a group, through the formation of a Research Coordinating Committee of the Building Enclosure Technology and
Environment Council (BETEC) a council of the National Institute
of Building Sciences. In addition to the almost daily communica-
tions that are conducted nationally, they are putting on a major
international conference, the Building Enclosure Science and Technology Conference (BEST 1), the first of a series that will be held
every two years, in alternate years to the Canadian National
Building Envelope Council (NBEC) conferences held every two
years. BEST 1 promises to be an international conference that
fulfils the BETEC mission of technology transfer to mainstream
design, research and construction, closing the loop between research and practice, and at the same time challenging previous
perceptions and beliefs, identifying future research needed in that
esoteric and mysterious world of building science, and presenting
the cutting edge of building science knowledge and practices
today.
BEST 1 will be held on June 11 and 12, 2008 in Minneapolis,
Minnesota. It will be hosted by the progressive BEC chapter, BEC
Minnesota, which is already busy organizing an event that promises to be an amazing step in the focus on durability and the indoor
air quality of buildings. One track will be “Bugs Mold and Rot IV”,
and the other will be the energy efficiency of buildings, with
speakers who are leaders in building science from all of North
America and Europe. Stay tuned, it will be an event not to miss!
Now to this edition of JBED, which is dedicated to bringing
the best technical presentations that have been presented to the
BECs…and more! They have been brought to you here, for your
enjoyment and for posterity! So join me in enjoying these scholarly papers and we certainly welcome your comments, suggestions
and reactions.
Wagdy Anis, FAIA, LEED AP
Chairman BETEC Board
Chairman, JBED Editorial Board
Principal, Shepley Bulfinch Richardson and Abbott, Boston, MA
UPCOMING EVENTS
Don’t forget the top conference of them all, the BETEC /
DOE / ORNL / ASHRAE Thermal Performance of the Exterior
Envelopes of Whole Buildings X International Conference, December 2-7, 2007, Sheraton Sand Key Resort, Clearwater
Beach, Florida. It is held once every three years, and is the
building science conference to attend! BETEC will be celebrating its 25th anniversary there, with a special dinner you
can sign up for.
BETEC will also be holding its open board meeting and its
Research Coordinating Committees will also be meeting
during this conference, so please participate and join BETEC
in its mission in bringing the best of building science to North
America.
See you there!
For more information, go to www.ornl.gov/sci/buildings
or check out the advertisement on page 49!
8 Journal of Building Enclosure Design
Feature
Evaluating Energy Efficiency Using
Whole-Building Simulation Tools
By Jason S. Der Ananian and
Sean M. O’Brien, Simpson, Gupertz & Heger Inc.
RECENT TRENDS TOWARDS GREENER BUILDING have
brought whole-building energy performance into the spotlight.
Building and mechanical system designers typically use manufacturer’s published R-values and U-factors in their wall and roof assemblies to meet prescriptive building energy code requirements.
However, the use of such product properties alone is not indicative of actual performance, since additional heat flow paths are
not accounted for in these values (for example, losses or gains due
to thermal bridging through steel stud-framed walls or discontinuous insulation at floor slab edges). Similarly, the reported U-factors for window, door and curtain wall systems are based on laboratory performance testing that does not account for the
substantial heat loss at the window perimeters that often occurs in
typical window installations1. Accurate simulation of window performance is critical, as fenestration heat loss/gain in a building
often exceeds that of the opaque (insulated) walls and dominates
the envelope loads.
This article examines the differences in calculated envelope
loads for a variety of cladding and fenestration systems using both
area-weighted manufacturer’s insulation values and integrated simulation of connections, such as window-to-wall interfaces. We also
examine the effects of relatively minor component changes on the
performance of the whole building, including strategic selection of
window and glazing types, and varying insulation thickness and
placement. Based on our review, we provide strategies for maximizing the effectiveness of whole-building energy simulations.
PARAMETRIC STUDY OF OVERALL R-VALUE IN A SIMULATED
BUILDING
Simpson, Gumpertz & Heger Inc. recently performed a series
of analyses determining the effects of cladding, windows and glazing types on the overall insulating value of a generic rectangular,
two-story, light commercial office building. The building was modeled as slab-on-grade construction, with continuous R-24 roof insulation and continuous strip windows on the second floor only.
The first floor contained no fenestration; for modeling purposes
we assumed that the first floor was fully opaque. We modeled this
basic building using a variety of wall systems, presented in Figure
1 A and Figure 1 B, summarized as follows:
• Wall System 1 – Composite (uninsulated) 1/2 in. (12.7 mm)
thick metal panels over insulated (R-19 [RSI-3.35]) 6 in. (0.152
m) steel studs, non-thermally broken aluminum strip windows
with insulating glass units (IGUs), and steel studs discontinuous
across the 2nd floor slab edge.
• Wall System 2 – System 1 with steel studs continuous across
the 2nd floor slab edge.
• Wall System 3 – System 1 with brick masonry veneer in place
of metal composite panels.
• Wall System 4 – Composite 2 in. (0.051 m) insulated (R-14
[RSI-2.47]) metal panels over uninsulated 6 in. (0.152 m) steel
studs, thermally-broken aluminum strip windows, and steel
studs continuous across the 2nd floor slab edge.
We determined the heat flow properties of the building
Wall System Descriptions
Wall
System
Cladding
1
1a
1b
2
2a
2b
3
3a
1/2”
(2.7mm)
uninsulated
composite
metal
panels
1/2”
(2.7mm)
uninsulated
composite
metal
panels
4”
(0.102m)
brick
masonry
veneer
3b
4
4a
4b
2” (0.051m)
insulated
(R-14
[RSI-2.47])
composite
metal
panels
6” (0.152m)
Steel Stud
Framing
R-19 (6” [0.152m])
Batt Insulation
Aluminum
Strip
Windows
Thermally Broken
Window Frames
yes
yes
yes
yes
yes
N/A
N/A
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
N/A
yes
Low E
Coating
Insulation Continuous at
2nd Floor Slab Edge
yes
N/A
yes
Insulating Glass
Unit (IGU)
N/A
yes
yes
N/A
yes
yes
yes
yes
N/A
N/A
N/A
yes
yes
yes
yes
N/A
N/A
N/A
yes
yes
yes
w/argon fill
yes
yes
Yes = System includes this feature
N/A = Not applicable
Figure 1 A - Wall System Descriptions.
10 Journal of Building Enclosure Design
Figure 1 B - Wall System Diagrams. System 4 Note: Panels include horizontal joints at
3 ft (0.9m) on center and vertical joints at 36 ft (11 m) on the center.
enclosures using the Therm 5.2 computer program, developed by
the Lawrence Berkeley National Laboratory, a 2-dimensional,
steady-state finite element simulator. For consistency, we performed all simulations using an interior temperature of 69.8°F
(21°C) and an exterior temperature of -0.4°F (-18°C), with a 12.3
mph (5.5 m/s) airflow perpendicular to the exterior surface of the
component, based on the NFRC 100-2001 standard for determining fenestration product U-factors. We modeled all IGUs with
rigid aluminum spacer bars.
We performed separate analyses of each major component of
the building enclosure to determine their individual insulating values and then calculated the weighted insulating value of the entire
wall from the component values. For window perimeters, we
simulated the effects of heat transfer through the perimeter walls
in addition to heat transfer through the windows themselves. The
enclosure consists of the following components:
• Base of wall (at slab-on-grade);
• Field of opaque wall;
• Slab edge (at second floor level);
• Window sill;
• Field of window (center of glass area), including vertical mullion effects;
• Window head; and
• Roof edge (horizontal heat flow only).
We determined the boundaries of our model for each component by reviewing the initial simulation results to establish the adiabatic end conditions—the points at which heat flow occurs in only
one dimension, then “cutting” the section in that location. Figure
2 illustrates this concept for an example window sill cross section.
For simple, layered systems of building materials with heat
flow in one dimension, such as concrete block walls with continuous insulation, the overall R-value (expressed in (hr*ft2*°F)/btu
[m 2 *K/W]) is simply the sum of all component R-values:
Roverall = Rlayer1 + Rlayer2 + ….. + RlayerX (equation 1)
In this case, adding continuous R-5 (RSI-0.88) insulation to an
R-10 (RSI-1.76) wall will increase the overall insulating value to R15 (RSI-2.64). This is also known as “series” heat flow.
The overall R-value was chosen as the final indicator of thermal
performance, as R-values are more commonly recognized than
Figure 2 - Selection of component size.
their inverse, the overall heat transfer coefficient, or “U-factor”
(btu/(hr*ft2*°F [w/m2K]). The U-factor is a measure of the total
heat flow through a given material thickness (or a given component) by conduction, convection and radiation. It is commonly
used to define a weighted average conductance for the various
materials in an assembly. When applied to windows, the U-factor
accounts for convection and radiation within and between air
spaces in glazing systems. The relationship between the U-factor
and the overall R-value is: Roverall = 1 / Uoverall (equation 2)
Hence, the overall R-values that we calculated account for
convection and radiation in addition to conduction.
For multi-dimensional heat transfer, U-factors must be used to
calculate overall heat flow. This is due to the physical phenomenon of heat flow occurring along the path of least resistance, also
known as “parallel” heat flow. Since all of the components that we
analyzed were of different size, we performed an area-weighted
calculation to determine the composite U-factors for the wall system, based on a unit width of 12 in. (0.3 m):
Uoverall = (Area1 * U1 + Area2 *U2 + ….. + AreaX *UX) /
(Area1 + Area2 + ….. + AreaX)
(equation 3)
Using U-factors in Equation 3 takes into account the increased
heat flow through conductive components, such as steel studs,
placed in parallel with non-conductive components such as insulation. Where these parallel heat flow paths exist, adding R-5 insulation to the stud cavity will not necessarily produce a corresponding R-5 increase in the overall R-value of the system, as the
potential effect of insulation is reduced by the increased heat loss
through the other components of the system.
GENERAL RESULTS OF OVERALL R-VALUE STUDY
Using the equations above, we calculated overall R-values for
each system. Figure 3 presents the calculated overall R-values for
the systems analyzed.
THERMAL BRIDGING AND INSULATION DISCONTINUITIES
Thermal bridging through steel studs or discontinuities in insulation at floor slab edges leads to relatively high heat loss from the
various wall components.2 Given its relatively low weight, high
strength and ease of erection in the field, light-gauge steel framing
System
Overall R-Value (RSI-value)
1
4.8 (0.85)
1a
10.8 (1.9)
1b
5.5 (0.97)
2
5.0 (0.88)
2a
5.7 (1.0)
2b
11.6 (2.0)
3
4.8 (0.85)
3a
5.4 (0.95)
3b
10.2 (1.8)
4
7.1 (1.25)
4a
12.6 (2.22)
4b
7.5 (1.32)
Figure 3 - Overall system R-values.
Summer 2007 11
is widely used for both interior and exterior building walls. However, steel is also a highly conductive material, with a thermal conductivity more than 1000 times that of typical building insulation. In a
typical sheathed wall with glass fiber batt insulation between steel
studs spaced 16 in. on center, the studs create an efficient path for
heat to bypass the insulation (Figure 4). The addition of steel studs
typically reduces the overall R-value of the wall by approximately 50
percent. This loss is accounted for in some energy codes through
requirements for continuous insulation outboard of steel-framed
walls. The addition of continuous insulation outboard of the studs,
which helps to isolate them from the exterior of the building, results
in a slight reduction in the effects of thermal bridging through the
studs. The net effect of this reduction is often an increase in overall
R-value that exceeds the R-value of the insulation component alone.
Similarly, although to a lesser degree, joints between the insulated metal panels analyzed in System 4 have thinner or no insulation.
The effect of these discontinuities at the panel joints alone reduces
the overall insulating value of the panels by approximately 10 to 15
percent.
In some steel stud-framed buildings, the studs on each level are
supported on floor slabs that bypass the stud cavity insulation. Thermal inefficiencies, such as these slab edges (Figure 5), can have sizable impacts on building performance. The clearest
example of this is between Systems 1a and 2b, where insulating the
slab edge improves the overall R-value of the enclosure by approximately 8 percent. Comparing the basic component R-values to the
overall system R-values in Figure 3, it becomes clear that simple
calculations based on product data can significantly overestimate
the overall thermal performance of a wall system.
FENESTRATION
Windows, curtain walls and other components typically have
much less thermal resistance than opaque wall and roof sections.
Modern aluminum-framed assemblies employ features such as
multi-pane IGUs and low-conductivity thermal breaks to reduce
heat flow. However, due to the already low thermal resistance of
these components, even properly functioning assemblies may experience condensation problems. Consequently, small thermal
bridges through framing members and perimeter constructions can
have a significant impact on overall heat loss. To minimize the risk
of these problems, the insulating components should be made continuous with the insulation in the adjacent construction.
Due to the nature of parallel heat flow, a disproportionate
amount of heat is lost through building windows when compared to
their contribution to building surface area. Comparing Systems 1
with 1a, the R-value of the windowless wall system is nearly double
the R-value of the wall system when windows are included. This is
somewhat counterintuitive, as the windows account for less than 20
percent of the overall building surface area (not including the roof)
The use of thermally broken windows can have a significant impact
on overall R-values, as the windows are typically a primary source of
heat loss. Figure 6 shows a graphic temperature plot of the System
1 vs. System 4 windows. Without complete thermal breaks, the
System 1 windows remain significantly colder and have less than half
of the insulating value of the thermally-broken System 4 windows.
In some buildings, cold frame temperatures may contribute to condensation problems as well as increased heating and cooling costs.
GLAZING SELECTION
Selection of glazing systems can have significant impacts on
overall system performance. Figure 7 presents the center-of-glass
thermal resistance and Solar Heat Gain Coefficients (SHGCs) for
the glazing systems used in the study. The SHGC is the fraction of
incident solar radiation that is transmitted through the system. A
Figure 4 - Computer simulation results showing effects of thermal bridging through
steel framing.
Figure 5 - Computer simulation results showing effects of thermal bridging at slab edges.
12 Journal of Building Enclosure Design
Figure 6 - Computer simulation results showing the effects of thermally broken
window frames.
SGHC of 0.702 means that 70.2 percent of incident solar radiation is
transmitted through the glazing. Consequently, a lower coefficient
represents a decrease in solar heat gain, which can increase heating
loads but decrease cooling loads. For example, the addition of a lowe coating (e=0.04) to the IGUs in System 1 provides a 15 percent increase in the overall R-value of the building enclosure—a significant
increase in performance relative to the cost of adding the coating.
Small changes such as the addition of argon gas to improve IGU
performance can also have moderate impacts on overall enclosure
R-values. For example, the addition of argon-fill to IGUs with a low-e
coating in System 4 provides a 6 percent increase in overall R-value
for the building enclosure. As with the low-e coating discussed
above, this is a significant increase in performance given the relatively
low cost of the argon fill.
PARAMETRIC STUDY OF WHOLE-BUILDING ENERGY REQUIREMENTS IN
A SIMULATED BUILDING
Utilizing the overall R-value (Figure 3) and SHGC data (Figure
7), we performed a series of whole-building energy simulations of all
variants of Systems 1 and 4 for the generic office building described
in Section 1.1. We used the EnergyPlus 1.4 computer program, developed by the U.S. Department of Energy to simulate the effects of
time-varying interior and exterior environmental conditions, as well
as the effects of solar radiation (i.e., solar heat grain through windows) and internal heat loads.
All options were analyzed using slab-on-grade construction and a
flat roof system with R-24 insulation. The simulated rectangular
building (100 ft [30.48 m] x 75 ft [22.86 m] in plan) was oriented
with the long dimension on an east-west axis. The building included
two stories with opaque walls on the first floor and continuous
perimeter strip windows on the second floor.
In order to provide a more realistic estimate of building envelope
loads, simulated occupant and occupant-related loads for a typical office building were used. All simulations included basic heating and
cooling systems, as the goal of this analysis was a generic comparison
of system performance. For these models, the simulated mechanical
system provided exactly enough heating, cooling, and ventilation to
meet the building loads based on a prescribed occupancy schedule.
In general, the building heating loads make up less than 10 percent of the total load, with the remaining 90 percent attributed to
cooling. The effects of latent (moisture) loads or the use of “economizer” cooling are not included in this simulation. Simulation of these
variables is relatively complex, involves the selection of specific mechanical system components and equipment sizes, and is beyond the
scope of a general comparison.
Due to the complexity of building cooling loads, the comparative
loads that we calculated may not represent the actual cooling loads
that a real-world building would experience. However, the results
do illustrate several relevant trends:
• System 4a vs. System 1a (Chicago): System 4a, despite having a
more efficient building envelope, has a slightly higher overall cooling load than the less efficient System 1a. This appears to be due
to the higher insulating value of the walls and windows retaining
more heat from interior sources. The same occurs between System 4 and System 4a in Miami. The use of argon-filled IGUs increases the thermal resistance of the envelope, but as a result reduces the loss of heat from interior sources and increases the
cooling loads.
• System 4 vs. System 4a (Miami): The overall cooling load for a
building without windows (System 4a) is over 25 percent less
than the building with windows. This illustrates the potentially
significant contributions of windows to building cooling loads.
Glazing Assembly (all
dimensions nominal)
1/4” (6.35mm) clear
%
Increase
SHGC*
Decrease
%
2.1
-
0.702
-
3.4
62%
0.378
46%
4.1
21%
0.374
46%
glass, 1/2 (12.7mm)
airspace, 1/4” (6.35mm)
clear glass
1/4” (6.35mm) clear
glass w/low-e
(e=0.04) coating on #2
surface, 1/2” (12.7mm)
airspace, 1/4" (6.35mm)
clear glass
1/4" (6.35mm) clear
GENERAL RESULTS OF WHOLE-BUILDING ENERGY ANALYSES
Figure 8 presents the total heating and cooling energy calculated
for all variants of Systems 1 and 4. In addition, the peak cooling load
for each system is presented in the last column. The peak cooling
load is the maximum cooling power of the system, and represents
the cooling power required to maintain the design interior temperature on a summer design day.
The results from the whole-building energy simulation for the
building heating loads are generally consistent with the results from
our overall R-value simulations. The internal heat loads, such as people and equipment, that we simulated will reduce the heating demand for mechanical system in the building, since they provide additional heat to the space. For alternate occupancies in a similar
building, such as residential or retail spaces, the mechanical system
loads may be greater due to the lack of this additional heat. Internal
building loads, combined with solar heat gain through windows, provide 100 percent of the winter heating requirements for the Miami,
FL cases.
Effective
R-value
glass w/ low-e (e=0.04)
coating on # 2 surface,
1/2" (12.7mm) argon fill,
1/4 (6.35mm) clear glass
* SHGC = Solar Heat Gain Coefficient
Figure 7 - Insulating Glass Unit performance characteristics.
Yearly Totals
System
1 – Chicago
4 – Chicago
Windows
Non low-e
Low-e
1 – Miami
4 – Miami
Non low-e
Low-e
1a – Chicago
4a - Chicago
None
None
1a – Miami
4a – Miami
None
None
1b – Chicago
4b – Chicago
Low-e
Argon low-e
1b – Miami
4b – Miami
Low-e
Argon low-e
Whole Building (btu)
Heating Energy
39,470,492
22,544,532
42.88%
0
0
0.00%
21,199,529
17,372,286
18.05%
0
0
0.00%
32,914,018
19,935,520
39.43%
0
0
0.00%
Cooling Energy
323,137,208
315,256,842
2.44%
627,430,538
584,980,452
6.77%
251,632,630
256,052,105
-1.76%
474, 399,687
474,130,258
0.06%
304,873,553
320,255,018
-5.05%
585,744,457
587,420,462
-0.29%
Total Load
362,607,700
337,801,374
6.84%
627,430,538
584,980,452
6.77%
272,832,159
273,424,391
-0.22%
474,399,687
474,130,258
0.06%
337,787,571
340,190,538
-0.71%
585,744,457
587,420,462
-0.29%
Peak Cooling Load
207,174
189,017
8.76%
206,607
188,132
8.94%
155,850
154,500
0.87%
167,434
167,763
-0.20%
192,933
188,841
2.12%
191,923
188,172
1.95%
Percentages listed represent reduction (or increase) in loads
Figure 8 - Summary of Heating and Cooling Energy for Wall Systems.
Summer 2007 13
• System 1b vs. System 1 (Miami); The use of low-e coated IGUs
(System 1b) reduces the overall building cooling load by approximately 7 percent. In addition, the building heating load is reduced
by 20 percent when low-e IGUs are included. These incremental
improvements justify the added material expense of low-e IGUs.
Also of interest is the peak cooling load, which determines the
required capacity of the mechanical cooling equipment. While
overall energy usage will determine space conditioning costs,
lowering the peak cooling load for a building may produce an upfront cost savings if the cooling equipment can be downsized.
CONCLUSIONS
Code prescribed R-values for wall/roof assemblies, when used
exclusively in building designs, generally do not account for heat flow
due to thermal bridging at structural components, window surrounds and floor slabs. In addition, they do not account for solar heat
gains as dictated by fenestration selection and placement, or glazing
type. Consequently, the use of product R-values to generate energy
load estimates is an oversimplification of actual performance characteristics and may result in misguided expectations and inadequate
performance of installed heating and cooling equipment. Our comparative R-value calculations and whole-building energy simulations
show that relatively small details, such as the use steel stud framing
or low-e glazing, can significantly influence the required loads for a
building depending on the climate zone in which the building is
located, underscoring the need for careful analysis of whole-building
energy performance.
Whole building simulations can also provide designers with a relatively inexpensive method of performing cost-benefit and life-cycle
costing analysis on alternate building components. This may range
from selecting alternate glazing systems to optimizing the location of
windows to maximize winter heat gain (reducing heating loads) and
minimize summer heat gain (reducing cooling loads). This type of optimization is not possible with traditional, steady-state load calculations.
Based on our analysis, we present the following guidelines for determination of whole-building energy performance:
• Do not rely solely on product or code-prescribed R-values as a
measure of thermal performance.
• Calculate the performance of individual building envelope components, especially the intersections between assemblies such as
opaque walls and windows, to determine the effects of these intersections on the overall system performance.
• Calculate effective R-values for entire wall sections from their
component parts for use in whole-building simulations. Each
unique wall section and glazing system should be modeled separately.
• Apparently minor changes in occupancy or mechanical equipment can have significant impacts on overall building performance. These aspects of the building should be modeled to match
the actual building use and construction as closely as possible to
provide a more realistic estimate of overall energy consumption.
• Parametric analysis of building system options, including glazing
orientation, can be used once a model is complete to perform
cost-benefit analysis of building options and optimize the overall
performance of the building. Given the relative ease with which
an options analysis can be performed, the potential for long-term
energy savings is likely to far outweigh the up-front cost of the
analysis.
As energy prices climb higher and the demand for “greener”
buildings increases, the use of whole-building energy simulation is
evolving from a purely academic exercise to a critical tool in building
design.
Some of the analysis discussed in this article is derived from a recent project with CENTRIA Architectural Systems that included
thermal simulation of their Formawall Dimension Series insulated
metal panels.
Jason Der Ananian is a Senior Engineer in the Boston office of Simpson, Gumpertz & Heger Inc. He can be reached at
jsderananian@sgh.com. Sean O’Brien is a Senior Staff Engineer in the
New York City office of Simpson, Gumpertz & Heger Inc. He can be
reached at smobrien@sgh.com.
REFERENCES
1. O’Brien, S.M., “Finding a Better Measure of Fenestration
Performance: An Analysis of the AAMA Condensation Resistance Factor”, RCI Interface, May 2005.
2. O’Brien, S.M., “Thermal Bridging in the Building Envelope:
Maximizing insulation effectiveness through careful design”, The Construction Specifier, October 2006.
14 Journal of Building Enclosure Design
Feature
ASTM C 652 Bricks: Less is Good
By Richard Bennett, University of Tennessee and
Jim Bryja, General Shale Products Corp.
brick. The specifications have similar requirements for durability, appearance and
tolerances on chippage, distortion and size.
The primary difference is the amount of
coring.
Due to advances in the manufacturing
process, brick manufacturers are increasingly producing hollow facing brick, which
has greater than 25 percent coring. Figures
1 and 2 compare bricks with different
amounts of coring. This paper examines
some of the aspects of hollow bricks.
Figure 1 - Comparison of ASTM C 216 solid brick (25 percent coring) with C 652 hollow brick (28 and 32 percent coring).
INTRODUCTION
Brick is one of the oldest building products, being used in many ancient structures,
yet still remains a popular and competitive
wall cladding today. Brick is very durable,
producing a long product life, greater than
100 years, with very little maintenance requirements. Brick contributes to air quality
by eliminating the need for paint or adhered
finishes, thereby reducing volatile organic
compounds (VOCs). Brick reduces the potential for mold growth. Fire safety and
wind-borne debris impact resistance are increased with brick construction. Bricks do
not emit toxins to the environment when
exposed to fire. Bricks provide thermal
mass, reducing energy requirements by
slowing the transfer of heat and cold. Brick
are typically manufactured regionally, so the
transportation distance is minimized. Bricks
can be recycled, with old brick, culled brick
from the manufacturing process, and waste
brick from construction, being ground up
and used for landscaping chips and brick
dust. Brick produces no hazardous waste.
16 Journal of Building Enclosure Design
Brick provides many advantages as an exterior wall covering.
Brick manufacturing was mechanized in
the late 1800s with the development of machines to produce molded brick (Borchelt
and Carrier, 2007). These bricks were solid,
with no cores. The extrusion manufacturing
process was developed in 1875, and is still
in use today. Although the original extruded
brick did not contain any cores, manufacturers were soon producing cored brick, as
this resulted in reduced weight and improved drying and burning characteristics.
The current specification for facing brick,
ASTM C 216, was first introduced in 1947.
The brick could have up to 25 percent coring, and was considered to be solid for
strength calculations. This has remained unchanged until today. In 1967, a change was
proposed to C 216 that would allow up to
40 percent coring. Rather than incorporate
the increased coring into C 216, ASTM C
652 was introduced in 1970 as a specification for hollow brick. Currently, ASTM recognizes both C 216 and C 652 as facing
PROPERTIES OF HOLLOW BRICKS
Physical properties
Hollow facing brick will have voids in
the 26-35 percent range for typical brick
veneers, as opposed to the current 25 percent. This will reduce the weight of the
brick. Modular size bricks, 7 5/8 x 2 1/4 x 3
1/2 in. (194 x 57 x 89 mm), will weigh
about 1/3 pound (1 1/2 N) less; engineer
size bricks, 7 5/8 x 2 3/4 x 3 1/2 in. (194 x
70 x 89 mm), will weigh about 1/2 pound
(2 1/4 N) less.
The National Brick Research Center
(Sanders, 2006) examined the physical
properties of over ten different brick types.
For each brick type, a hollow brick was
compared to a solid brick. Properties examined were compressive strength, flexural
bond strength, cold water absorption, boiling water absorption, saturation coefficient
(C/B ratio) and the initial rate of absorption.
For all brick types there was no significant
difference between the properties of the
hollow brick and the solid brick. Hollow
brick can be expected to behave similarly to
solid brick, having the same durability and
similar structural performance properties.
Fire resistance
The fire rating of masonry is determined
based on the equivalent thickness. The
equivalent thickness is simply the actual
brick thickness times the percent solid. For
a given actual thickness, a hollow brick will
have a smaller equivalent net thickness than
a solid brick. However, codes allow a higher
rating per equivalent thickness for hollow
brick than solid brick. This is based on actual
testing and the fact that air is an excellent insulator. Based on the 2006 International
Building Code, ASTM C 216 solid brick (actual 25 percent coring) will have approximately a 1 hour rating. A hollow brick with
30 percent voids will have a rating of approximately 1.1 hours or greater than the
ASTM C 216 brick.
Thermal performance
Brick veneer walls are known to improve
the thermal performance of structures due
to their thermal mass. Thermal mass has the
desirable properties of reducing the amplitudes of, and delaying in time, heat transfers
through building sections under real world,
dynamic conditions. Experimental work and
monitoring of test structures has shown that
brick veneer structures do save heating and
cooling energy.
Brown and Stephenson (1993) tested
seven different wall specimens using a guarded hot box. One specimen was a 3 1/2 in.
(90 mm) steel stud wall with 1/2 in. (12 mm)
gypsum on the interior and exterior, R-12
glass fiber insulation between the studs, and
1.0 in. (25 mm) stucco on the exterior face.
A similar specimen had 3 1/2 in. (90 mm)
brick veneer with a 1 in. (25 mm) airspace.
The brick veneer over steel stud wall specimen had a measured thermal transmittance,
the U-value, of 30 percent less than the
transmittance of the stucco over steel stud
wall specimen. Biblis (2005) monitored the
actual energy consumption of ten different
test houses in Auburn, Alabama. The unit
with plywood siding used 5.1 percent more
energy in the cooling period from June 8 to
September 15, and 9.2 percent more energy
in the heating period from January 1 to April
4 than the brick veneer structure.
The enhanced energy performance of
brick veneer structures comes from two
sources. One source is the mass of the brick
and the other source is the insulating value
of the brick and cavity. Obviously reducing
the mass of a brick by increasing the coring
would reduce the thermal mass benefits of
the brick. However, hollow brick have better insulating properties than a solid brick
due to the air in the voids.
Simulation of the energy use of buildings
in Chicago, San Francisco, Denver, Tampa
and Washington showed virtually identical
thermal performance of C 216 and C 652
bricks (Bennett et al, 2007). The decrease
in thermal mass was offset by the increased
thermal resistance. The use of hollow brick
will not reduce the known energy benefits
of brick.
CONSTRUCTION WITH HOLLOW BRICKS
Although the use of hollow brick may
result in a slight increase in mortar usage,
studies performed at the National Brick Research Center (Sanders, 2006) and by a
brick manufacturer showed the increase to
not exceed the industry standard estimate
of seven bags of mortar per 1000 brick.
Masonry walls of hollow brick have the
same resistance to moisture penetration as
walls made of solid brick. The most important factor in reducing permeability is workmanship, irrespective of the type of masonry unit (Grimm, 1987). Modern day cavity
drainage wall construction also provides excellent moisture resistance, even if water
does penetrate the brick wall.
The reduced weight of hollow brick
makes it easier on the laborer and the
mason. The coring percentages with hollow
facing brick are not sufficiently large to require face shell bedding. The mason can
easily make a full bed, with furrowed mortar, identical to current construction practice. In other words, hollow brick can be
laid in the same manner, and with the same
productivity, as solid brick, with the lighter
weight reducing mason fatigue.
Hollow brick construction will result in
wall claddings with less mass, which is of
benefit in seismic and structural design. The
force in seismic design is directly proportional to the mass, so a reduced mass results in a smaller force. With more municipalities across the country adopting seismic
codes, including areas where there has
never been seismic design, the use of hollow brick will be advantageous. The lighter
weight also reduces the load on foundations, lintels and shelf angles.
ENVIRONMENTAL BENEFITS OF HOLLOW
BRICKS
Environmental aspects, or the “greenness” of a project, are measured in several
ways. Three ways will be examined here;
the National Home Builders Association
(NAHB) Green Homebuilding Guidelines,
the National Institute for Standards and
Technology Building for Environment and
Economic Sustainability (BEES), and the
U.S. Green Building Council Leadership in
Energy and Environmental Design (LEED).
The National Home Builders Association (NAHB) specifically mentions C 652
hollow brick as an alternative to C 216
brick under the second guiding principle,
Resource Efficiency, of the Green Home
Guidelines. The National Institute for Standards and Technology Building for Environment and Economic Sustainability (BEES)
program is a systematic methodology for
selecting building products that achieve
the most appropriate balance between
Figure 2 - Comparison of ASTM C 216 solid brick (22 percent coring) with C 652 hollow brick (30 and 34 percent coring).
Summer 2007 17
environmental and economic performance
based on the decision maker’s values. The
BEES analysis is based on the weight of a
brick. Lighter weight brick reduce emissions during manufacturing and require less
fuel for shipping. The typical flatbed truck
can haul 26 cubes of C652 brick as compared with 23 cubes of C216 brick, an
eleven percent savings for a trip.
Brick construction enables a designer to
achieve several LEED points in a single material. These include Materials and Resources 5.1 credits the use of materials extracted and manufactured within 500 miles
of the construction site. These LEED credit
points can be met by selection of face brick as
an exterior material, and can be enhanced by
the choice of hollow brick over solid brick.
environmental impacts both in manufacturing and transportation. Hollow brick enhance the already substantial benefits of
brick construction.
CONCLUSIONS
Hollow bricks are increasingly being produced by brick manufacturers. They come in
the same sizes, types, colors and textures as
solid brick. Hollow brick have similar physical properties to solid brick and provide
equivalent or slightly better performance
characteristics. Hollow brick provide
important environmental benefits, reducing
Richard Bennett, PhD, PE, is professor of civil
and environmental engineering at the University of Tennessee. He is a member of ASTM
and the Masonry Building Code Committee.
Jim Bryja, PE, SE, is manager of engineering
services at General Shale Products Corp.,
Johnson City, Tennessee. He chairs the National Brick Research Center (NBRC) Wall
Systems Committee.
REFERENCES
ASTM C 216-07, Standard Specification for Facing Brick (Solid Masonry
Units Made from Clay or Shale).
ASTM C 652-05a, Standard Specification for Hollow Brick (Hollow Masonry
Units Made from Clay or Shale).
Bennett, R.M., Kelso, R., and Bryja, J.
(2007). “Thermal Performance of Hollow Brick Veneer Walls.” 10th North
American Masonry Conference, The
Masonry Society, 158-164.
Biblis, E.J., “Experimental Determination of the Energy Requirements for
Cooling and Heating Different Singlestory Residential Structures.” Forest
Products Journal, 55(3), 2005, pp. 81-85.
Borchelt, J.G., and Carrier, J. (2007).
“The History of Void Area and Face Shell
Thickness Requirements in USA Brick.”
10th North American Masonry Conference, The Masonry Society, 584-595.
Brown, W.C., and D.G. Stephenson,
“Guarded Hot Box Measurements of the
Dynamic Heat Transmission Characteristics of Seven Wall Specimens – part II.”
Transactions, ASHRAE, 99(1), 1993, pp.
643-660.
Grimm, C.T. (1987). “Water Permeance of Masonry Walls: A Review of the
Literature.” Masonry: Materials, Properties, and Performance, ASTM Special
Technical Publication 778, 178-199.
NAHB Model Green Homebuilding
Guidelines (2006). National Home
Builders Association.
Sanders, J.P. (2006). The Effect of
Void Area on Wall System Performance.
National Brick Research Center, Clemson University, Anderson, SC.
18 Journal of Building Enclosure Design
Feature
Transitions: How to Design Facade Interfaces
By Karol Kazmierczak and
Dan Neeb, Halliwell Engineering Associates
THE WALL PERFORMS A number of functions. The elements responsible for
performing these functions must be continuous throughout an enclosure, particularly at the transitions (for example, at the interfaces of fenestration with adjacent
assemblies). A discontinuity almost always causes a functional weakness or outright failure. In my practice I use a system of layering that helps me accomplish
the principles of facade engineering. I visualize layers for
waterproofing, thermal insulation, vapor retarder, air barrier,
etc. The goal is to keep all layers continuous, no matter
what part of vertical or horizontal section of building envelope is analyzed.
Figure 1 and Figure 2 are
an example of an analysis performed on curtain wall details.
The building enclosure’s layers
are represented with colored,
dashed lines. In this example,
not only are all the major layers kept continuous, but also
no sealant is used to perform
any essential facade function.
This type of rainscreen detail is
seldom seen in the U.S. The
rain screen wall is unfamiliar to
many contractors and comes
Figure 1. Details to be analyzed.
with a greater initial cost for
owners.
The typical layers include:
weather screen, insect or bird
screen, vapor-permeable waFigure 2. Analysis of details.
terproofing, vapor-impermeable waterproofing, thermal inBird screen interrupted at each mullion of a stepped curtain wall.
sulation, acoustical insulation, fire isolation,
smoke isolation, vapor barrier and air seal.
Special layers may include blast resistance,
burglar resistance and bullet resistance.
Most of these functions can also be
tagged with the required unit and value, for
example fire rating min 1hr, vapor retarder
max 1 perm (57 ng/s•m2•Pa), air barrier min
45 psf (2,155Pa), etc. This is particularly
useful where the values change, for example where horizontally positioned R20 (RSI3.10) insulation transitions into vertical R10
(RSI- 1.76) insulation.
Figure 3.
Figure 4.
20 Journal of Building Enclosure Design
Some materials perform more than
one function. The most demanding applications will require particular focus on the
choice of the proper material and connections. In this example, the perimeter
membrane acts as the waterproofing
membrane, the vapor retarder, and the
air barrier all in one. In this case the most
demanding function is the air barrier because a membrane material has to resist
perhaps 20psf (958Pa) positive and negative pressure differential or more, and
transfer the load to the assembly. Design
wind pressure establishes the performance criteria and describes the in-service
need for physical durability of the layer, as
opposed to the 1.57psf (75Pa) air permeance testing pressure listed in ASTM
E2178 which merely establishes acceptability as an air barrier material.
In Figure 1 and Figure 2, one would
specify a thick, puncture-and-tear-resistant elastomeric membrane, mechanically
clamped at its terminations. A metal flashing would be inappropriate because of the
vertical movement the flashing has to accommodate at the head.
Once one determines exactly what
function is performed by the particular
material, one is more likely to avoid common mistakes. One common mistake in
this example is the placement of insulation below the bottom mullion and above
the top mullion. As a result of this action,
condensation forms on the interior side of
the vapor barrier in cold climates. Once
one realizes where the vapor barrier is located, this mistake should not happen.
See Figure 5, reprinted from “Glass and
Metal Curtain Wall Systems” (R. L.
Quirouette, http://irc.nrc-cnrc.gc.ca/
pubs/bsi/82-3_e.html).
All sections of the enclosure opening
have to be designed in one process: jamb,
head, spandrel, sill, etc. The layers pictured at each section must be located at
the same respective wall depth and position around a perimeter of an opening.
Otherwise, a wall would be non-constructible, or gaps in the corners would
be created. A common error of this kind
is demonstrated by the two details reproduced below which belong to the same,
straight masonry opening, according to
the elevation.
Note in Figure 6 how the distance
between the face of the curtain wall and
Figure 5. Source: R.L. Quirouette, “Glass and Metal Curtain Wall Systems”.
Figure 6.
Figure 7.
the brick veneer varies. The analysis of
the weather shield continuity allows for
an early detection of such an error. The
analysis of the details above reveals also
some other problems. We encourage the
reader to analyze these details in context
(available at www.wbdg.org/design) and
compare with the logic presented in this
discussion.
The major facade layers are penetrated
at the anchors. The support function
should be decoupled from the need for
sealing; these two functions are typically
done by different trades and specified
separately. See Figure 7. The thermal insulation is discontinuous, bridged by conducting elements and the vapor retarder
is placed on its outer side, suggesting the
details are unsuitable for a cold or mixed
climate. Note the incorrect placement of
Summer 2007 21
Figure 8. Examples of transom discontinuity.
Figure 9.
Figure 10.
Figure 11.
22 Journal of Building Enclosure Design
air barrier, sealed to the non-continuous bottom transom. This error is particularly evident at the corners of a
curtain wall. This is also a potential problem when a designer decides to use a transom different than a mullion,
either for economy or aesthetics—see Figure 8 showing a corner of a curtain wall sill.
The principle of continuity holds true no matter what
scale is considered. In the scale of the whole building, a
designer has to determine where the layers are located
with regard to all rooms and partitions. Typically, the forgotten spaces are those above suspended ceilings of
overhangs, resulting in bursting, frozen plumbing in cold
climates. According to ASHRAE statistics, frozen sprinkler pipes are the biggest single cause of mold in New
York City.
See Figure 9 showing the properly conditioned
overhang space and the photograph showing the unconditioned space separated thermally from the building by
the insulated wall. See Figure 10 for magnified detail of
the curtain wall head from the good example above.
A different, but equally important example is a frequent violation of fire and smoke compartmentalization
in cavity walls. Typically a rated slab is bypassed by an
exterior wall cavity, which in turn opens to the building
interior at deflection joints, and is not sealed by rated
materials at the fenestration openings’ perimeters above
and below.
Fire and smoke transmission among compartments is
further assured by stack or chimney effect. See Figure
11 for detailed drawings of a masonry wall with a loose
lintel in a high-rise building and the photographs taken in
Figure 13 and Figure 14, in the field. In this example,
the outer sheathing of the backup wall is made of combustible plastic foam. The distance between the loose
lintels and the slabs varies from floor to floor; the resulting gap effectively connects compartments. The designer not only forgot about the fire code, the building is located in a cold climate zone too. As a result, the risk of
condensation is increased because the thermal insulation
layer is interrupted, and is unprotected by a vapor retarder; thermal bridging is effected by concrete, metal,
and wood elements. The spacing of brick veneer ties do
not meet code, but this problem is irrelevant to the current discussion. See Figure 12.
The photos in Figure 13 were taken when the brick
veneer was already being erected, after the substrate
had been accepted by the masons. The joints around
wall panels remained unsealed; an observer can see
through the crack. Moisture problems are likely to develop due to the condensation induced by an unpredictable pattern of air leakage and discontinuity of the
drainage plane. The mechanical system may negatively
pressurize the interior walls and suck the humid outside
air inside in summer; a positive pressure in the apartments would blow the moist interior air to the outside
in winter. The interruptions of both the lintel and the
thru-wall flashing ensure chimney effect in the wall
JOINT BTW. STUD WALL AND CONC. COLUMN
INTERRUPTION OF BOTH LINTEL AND FLASHING
Figure 13.
MISALIGNMENT BTW. STUD WALL AND CONCRETE SLAB
INTERRUPTION OF BOTH INSULATION AND AIR BARRIER
Figure 12.
cavity. A transfer of insects, odors and sound among apartments through the open cavity are among probable side effects.
The photos in Figure 14 show the misalignment between
the face of insulating sheathing and concrete. The tape reads
over 2 in. (5 cm). In the above drawings, construction tolerances, particularly the cast-in place concrete tolerance is not
anticipated. The air barrier was installed in a discontinuous
fashion which creates problems.
Continuity must also be maintained through movement
joints. An average curtain wall typically has several movement
joints differing in direction and magnitude of designed movement. Typically the floor deflection joints are most vulnerable.
Each layer has to be constructed in such a way as to accommodate the designed movement.
The process of design sometimes requires compromises. If
you follow this method, you will soon discover that many
popular design practices, materials and systems don’t work,
and no economical method may exist to solve the problem
and keep the layers continuous. Remember, there are two
price tags attached to each compromise: the long term cost
and the initial cost. Many good solutions are available from
countries employing sophisticated construction techniques, including Great Britain, Germany and Canada. My favorite example is thermally broken lintels and balcony slab systems
produced by foreign manufacturers. See Figure 15 and Figure 16. There is an increasing demand for them in North
America.
Karol Kazmierczak is a forensic building enclosure specialist at
Halliwell Engineering Associates. He is a registered architect in
New York and is the founding chairman of the Miami Building Enclosure Council. He specializes in curtain walls and architectural
glass with particular focus on thermodynamics.
Dan Neeb is a Senior Forensic Architect for Halliwell Engineering
Associates. He is entering his twenty fifth year in practice as a
Registered Architect and, in that capacity, has provided investigative and analytical services in a variety of projects, ranging from
complete systemic envelope failure as a result of catastrophic
events to component failures associated with construction defects.
Figure 14.
Figure 15.
Figure 16.
SUGGESTED LITERATURE:
American Society of Heating, Refrigerating, and Air-Conditioning
Engineers, “Applications Handbook” Chapter 42 “Building Envelopes.”
R.L. Quirouette, “Glass and Metal Curtain Wall Systems.” NRC,
1982. http://irc.nrc-cnrc.gc.ca/pubs/bsi/82-3_e.html
Thomas Herzog, “Facade Construction Manual.” Birkhauser,
2004.
Summer 2007 23
Feature
Reflections on the Window Wall
By Fiona Aldous, Wiss, Janney, Elster Associates, Inc.
THE GLAZED ALUMINUM WINDOW
wall synonymous with high-rise, multi-family residential construction reflects a continuing trend toward transparency within
the practice of architecture, more typical
of its commercial office building context.
Through the window walls’ aesthetic association to curtain wall, it appears to have
created for itself a cost-driven niche
throughout major United States cities, yet
clear performance criteria and comprehensive details are still needed to ensure a
successful project.
MODERNIST ORIGINS
Original window wall compositions,
which some could argue may be traced
back to the early decades of Modernism,
relied principally upon a “barrier” approach to resist rainwater penetration.
However, as air and water leakage problems became systemic, the design of the
window wall adopted similar principles to
rain screen design, including secondary
flashings, receptors and sub-sills, heelbeads in the glazing pocket, back-pans
sealed to framing at opaque panels and internally-drained systems to overcome
these issues.1
Throughout the United States today,
the Modern aesthetic has been adopted by
designers of high-rise residential buildings.
However, many construction documents
lack informed criteria for window wall
performance, including design pressure, air
and water penetration resistance, and
glazing systems coordinated with the
structural and mechanical characteristics of
the specific building design—all information critical in procuring and installing a
system that will meet the expectations of
the owner and end-user with regard to
long term durability and performance.
INDUSTRY DEFINITION
Perhaps some of the confusion is due
to the lack of a clear definition of a window wall. While industry guidelines can be
useful in defining the general configuration
of each system, performance definitions
are less clear. Consider the following widely held definitions:
• Fenestration: Openings in a building
wall, such as windows, skylights and
glass doors designed to permit the passage of air, light or people.2
• Curtain Wall: Any building wall, of any
material, which carries no superimposed vertical loads, i.e. any “non-bearing” wall.3
• Metal Curtain Wall: An exterior curtain wall which may consist entirely or
principally of metal, or may be a combination of metal, glass and other
Figures 1.1 and 1.2 - Cantilevered bays of window wall assemblies typical in high-rise residential construction.
24 Journal of Building Enclosure Design
surfacing materials supported by or
within a metal framework.4
• Window Wall: A type of metal curtain
wall installed between floors or between
floor and roof and typically composed of
vertical and horizontal framing members,
containing operable sash or ventilators,
fixed lites or opaque panels or any combination thereof.5
As the industry definition of window wall
suggests “metal curtain wall”, it is not surprising that the term “window wall” is frequently misunderstood, even by those in the
design and construction professions whose
responsibility it is to properly design, specify
and install these systems. To address this
concern, it is critical to understand window
wall fundamentals related to structure and
resistance to uncontrolled air and water infiltration.
THE INFLUENCE OF STRUCTURE
The design, engineering and installation of
a curtain wall, and the inter-relationship between the structure and the curtain wall, are
typically well understood issues. This includes compensating for movement within
the wall components themselves, relative
movement between the components, and
relative movement between the walls and
building frame to which it is attached.6 In addition, movements caused by temperature
Figures 2.1* and 2.2** - Common deflection header or movement anchors provided by manufacturers of window wall assemblies. It is important to verify receptor joinery also accommodates movement if used.
* Detail Courtesy of www.oldcastleglass.com/ww 2.5 4.5-6 elevation.php
** Detail Courtesy of www.wausauwindow.com/resources/details/4750-6250%20RX.pdf
changes, wind action, gravity forces and deformation and/or displacement of building
frame must also be factored.7 To further reinforce the issue, AAMA states, “to disregard such movements in designing the wall
is an urgent invitation to trouble.”8
The movement considerations outlined
above extend without exception to the design and installation of window walls. However, as window walls typically incorporate
pre-designed window products, along with
the potential for less experienced installers
and manufacturers migrating from the traditional residential market, the structural and
movement considerations are often overlooked. Window “gateway” minimum requirements, such as size, may not equate to
window wall openings—attachment and
loading calculations may not be performed
to guide installation and product choices,
and deflection of the structure may not be
accommodated in the window wall design.
In determining the extent to which the
structure will impact the window wall design, typically the fraction of a span L/360 is
utilized as the deflection limit for concrete
members; however it is suggested that the
maximum expected deflection, being, “the
sum of creep deflection from permanent
loads, the ‘elastic’ deflection from transient
loads, and the deflection effects of shrinkage
and temperature change”9 must also be considered.
This is particularly critical with post-tensioned concrete slabs such as those typically
utilized in high-rise residential construction,
where allowable design live and dead load
deflection at the center of continuous spans
often results in 3/8 in. (9.7 mm) of movement, unless factors more stringent due to
use/occupancy, or requirements of the initial
design program are outlined. At cantilevered
slabs such as those typically associated with
projecting bay windows and window wall
“stacks” this can be an important consideration (Figures 1.1 and 1.2). A review of the
structural design and the resulting deflection
allowance, in addition to thermal and sealant
compression characteristics will considerably impact the design of the window wall
and interface conditions, including air barrier
and sealant continuity without which, the
performance of the entire exterior wall may
be compromised. Properly specifying these
issues, and including either a deflection
header or movement anchor (Figures 2.1
and 2.2) as the basis of design is recommended in consultation with the structural
engineer.
AIR AND WATER PENETRATION RESISTANCE
In part, the appeal of the window wall is
derived from its operable and/or fixed lites
or panels, and the available manufacturing
diversity. However, to conceive this notion
as straight forward is to recognize the conflicts, deal with the occasional whim and understand the cumulative intent of all the applicable industry standards, and ultimately
define a clear performance specification
based upon a practical, durable and sustainable approach! The air and water performance criteria established by the American
Architectural Manufacturer’s Association
(AAMA) (Figure 3), are generally accepted
in the industry and can be used as a guide.
However, when considering these standards
as a guide it is also important to note:
• Typically, AAMA designated windows are
tested as individual units. Rarely, if ever,
are they tested in a window wall configuration that typically includes “ganged” or,
less often, but more problematic,
“stacked” mullions, receptor frames, and
similar accessories—all components that
significantly impact the overall performance.
• Maximum allowable air infiltration has
traditionally been defined by ASTM E283
and AAMA/WDMA/CSA 101/I.S.2/A44005, and are calculated based on square
foot area or frame size (crack length).
WDMA/AAMA/CSA Technical Joint Interpretation 06-05, dated 14 February
2007 stated: “the overall frame size is
defined as the part of window fitting into
rough opening.”10 As such, for a fixed and
an operable unit utilizing a common subframe, the area used to calculate net air
infiltration through that assembly includes, by definition, the entire square
foot area of the assembly, including the
sub-frame (Figure 4), and not the individual lite as tested to gain AAMA-designation. This can fundamentally alter project-specific test results for a window
wall assembly, often leading to confusion
regarding what constitutes a “passing”
grade during pre-construction mock-up
and or field air infiltration testing. The
standards, as currently written must be
thoroughly understood by the design
professional or construction specifierwhen crafting the specification.
continued on page 28
System and Industry Standard:
AAMA/WDMA/
CSA 101/I.S.2/A440-05
R - Residential,
LC - Light Commercial,
C - Commercial,
HC - Heavy Commercial
HC - Heavy Commercial
(Compression seal & Fixed)
AW - Architectural Windows
(Compression seal & Fixed)
CW-DG-96-1 and
AAMA MCWM-1-89
Curtain Wall
Water Penetration Resistance per
ASTM E331, ASTM E547 and
AAMA 501.1.
Air penetration Resistance per
ASTM E283
15% x *DP
75 Pa (1.57psf) and allow for
1.5 L/s.m2 (0.3 cfm/sf)
15% x *DP
300Pa (6.24 psf) and allow for
1.5 L/s.m2 (0.3 cfm/sf)
300Pa (6.24 psf) and allow
for 0.5L/s.m2 (0.1 cfm/sf)
20% x *DP
20% x *DP
0.08 L/sm (0.06cfm/sf) of wall area
plus per linear meter (foot) of crack
for the operable window units (if any)
Figure 3 - Typical water and air performance criteria established by the American Architectural Manufacturer’s Association (AAMA) Note: For complete product listing of maximum allowable air leakage, see AAMA/WDMA/CSA
101/I.S.2/A440-05, Clause 5.3.2.1, Table 6. p.52 * DP = Design Pressure
Figure 4 - Although comprised of both fixed and operable lites, the area of
the rough opening is used to determine air infiltration and not the individual
lite. Isolating the individual lite during testing can prove useful in determining possible areas of excessive air leakage.
Summer 2007 25
Figures 6.1 and 6.2 - Three dimensional concept sketches and CAD
details aid in understanding how the window wall and slab edge cover
system interfaces with adjacent construction while maintaining accommodation for movement of the structure, and air/moisture barrier continuity.
Figures 5.1 and 5.2 - Problematic slab edge interfaces require special attention.
When specifying window wall assemblies
utilizing multiple individual, AAMA-designated window units “ganged or stacked” together into a single floor-to-floor glazed
area, it is recommended to establish water
penetration resistance and allowable air
leakage of the entire window wall assembly,
and laboratory and/or field tests to validate
performance. Note that AAMA allows a 33
percent reduction in pressure for field tests,
which often results in testing that may not
replicate the actual design pressures to
which the building is exposed. This information is critical to establish early in the project, rather than relying on the published
performance test data or test standards for
each of the window wall component parts.
INTEGRATED PERFORMANCE
As areas of window wall glazing often
comprise whole exterior walls of residences, the designer should carefully and
holistically evaluate the impacts of solar heat
gain (SHG), glare, UV impact on interiors,
Condensation Resistance Factor (CRF), Ufactor, and allowable air leakage relative to
the HVAC design. A recent investigation of
air tightness studies on commercial building
envelopes identified tightening of the envelope in accordance with Air Barrier Association of America’s (ABAA) recommended air
leakage allowance of 0.02 L/s.m2 at 75 Pa
(0.04 cfm/sf at 0.3 in. H2O) and “predicted
potential annual heating and energy cost savings for these buildings ranged from 2 percent to 36 percent with the largest savings
occurring in the heating-dominated climates.”11 High-rise residential building facades, incorporating window wall designs
are moving towards emulating commercial
building facades. However, consideration
should be given to the internal residential
energy-consuming functions which dramatically contrast with those of commercial
buildings. Functions such as operable lites
28 Journal of Building Enclosure Design
and associated higher air infiltration allowances, individually controlled HVAC units
and less controllable relative humidity levels,
and full height vision glazing (typically without sun shading devices) all inter-relate with
the window wall. Hence, the widespread
use of the window wall should be pondered
in the context of energy-related performance factors which may not yet be fully appreciated.
DETAILS
The cladding at the slab edge adds further complexity and is typically the weakest
aspect of both the performance and design
of the window wall (Figures 5.1 and 5.2).
Not only must the slab edge cover accommodate the intricacies of the drainage of the
window wall system, but also provide coordinated air and water resistance while addressing the concerns of thermal discontinuity such that it does not contribute to the
development of condensation, meet the intent of the energy codes by installation of
sufficient insulation and properly interface
with adjacent construction. Three-dimensional drawings identifying conditions at slab
edges (Figures 6.1 and 6.2), balconies,
doors, secondary flashing and receptor systems, integration with adjacent wall (barrier
or drainage) and/or roof systems, and accommodations for movement and air pressures associated with high-rise buildings,
should all be considered in the overall detailing and specifying of the façade which incorporates window wall.
The window wall provides a modern cost
and schedule-driven alternative to the curtain
wall and although it is conceptually simple, the
requirements for successful design, installation and long term durability are complex.
The window wall requires thorough detailing
of the slab edge condition by the designer and
careful execution by the contractor. Overall,
the window wall warrants careful and
comprehensive consideration, and fundamentally clear performance criteria and detailing before inclusion in the design of highrise residential buildings.
Fiona Aldous is a building envelope consultant
with Wiss, Janney, Elster Associates, Inc.
(WJE). She has extensive experience in the
peer review, commissioning and investigation/
repair of various building enclosures with projects across the United States. She can be
reached at faldous@wje.com.
REFERENCES
1. Stéphane Hoffman, Adaptation of
Rain-Screen Principles in Window-Wall
Design. p.1-2 The Exterior Envelopes
of Whole Buildings VIII Conference.
2. ANSI /AAMA / WDMA, Voluntary Performance Specification for Windows,
Skylights and Glass Doors 101/I.S
2/NAFS-02, p.16.
3. AAMA, CW-DG-1-96 Curtain Wall
Design Guide Manual, 2005, p.2.
4. Ibid.
5. Ibid.
6. Ibid., p.13
7. Ibid.
8. Ibid.
9. W.G. Plewes and G.K Garden, CBD54. Deflections of Horizontal Structural Members, June 1964, http://www.
irc.nrc-cnrc.gc.ca.
10. WDMA/AAMA/CSA Technical Joint Interpretation 06-05 and AAMA/
WDMA/CSA 101/I.S.2/A440-05, section 8.2.1 and Fig. 27.
11. Steven J. Emmerich, Timothy P. Mc
Dowell and Wagdy Anis, “Investigation
of the Impact of Commercial Building
Envelope Airtightness on HVAC Energy Use” U.S. Department of Energy,
Office of Building Technologies, 2005.
p.34.
Feature
Air Barriers: Walls Meet Roofs
By Wagdy Anis, Shepley Bulfinch Richardson and Abbott and
William Waterston, Wiss, Janney, Elster Associates, Inc.
ABSTRACT
This paper briefly reviews what an air
barrier is and why it is needed, the design
influences on and the functional requirements of air barriers, and then documents
through case study format the ways to
achieve continuity between walls and
roofs. The basic environmental influences
on the enclosure managed by air barriers
in buildings are the air pressures on the
building enclosure. The air barrier system
provides the air-tightness of the building
enclosure by resisting the air pressures on
the building enclosure and transferring
those forces without displacement or rupture to other building enclosure systems
and finally to the building’s structural
frame. The air barrier must continue to
perform its functions for the intended
service life of the enclosure assembly.
A case study, the Worcester Trial
Court building in Worcester, MA, designed by Shepley Bulfinch Richardson and
Abbott, Architects, with Wiss, Janney, Elstner Associates, Inc, Engineers, Architects and Material Scientists, acting as
Roof Consultants providing quality assurance during the construction phase, will
be used as a case study to demonstrate
continuity of air barriers, specifically the
continuity between walls and roofs.
BENEFITS OF AIR BARRIERS
Continuous air barriers provide the
pressure boundary that separates the interior environment from the exterior, including below grade components of the enclosure. Controlling infiltration and
exfiltration enables the HVAC system to
perform as designed without disruption,
enhances human comfort, saves energy,
controls condensation and reduce the likelihood of pollutant entry into buildings and
the migration of pollutants within buildings. They improve the wind performance
of certain roof systems1, and are an essential component of high-performance
building enclosures2 for buildings that are
fully heated and/or conditioned.
The four basic requirements of air barriers are:
• Air impermeability
• Continuity
• Structural support
• Durability
Figure 1.
AIR IMPERMEABILITY
Air barriers are composed of materials
that are air impermeable to a great degree. Materials that have an air permeance of 0.004 cfm/ft2 at 1.57 psf (0.02 L/s.
m2 at 75 Pa) or less when tested to ASTM
E 2178 meet the basic requirement for
maximum allowable air permeance.
CONTINUITY
Materials are assembled together with
tapes and sealants, or applied as self-adhering sheets, or fluid-applied to form
opaque assemblies. Assemblies should
meet a maximum air permeance of 0.04
cfm/ft2 at 1.57 psf (0.2 L/s.m2 at 75 Pa)
when tested to ASTM E2357.
Assemblies are connected together
with flexible air impermeable joints to
form an air barrier system. An air barrier
system (the entire building enclosure, including below grade components) should
meet air permeance criteria of 0.4 cfm/ft2
at 1.57 psf (2 L/s.m2 at 75 Pa) of the thermal envelope pressure boundary when
the whole building is tested to ASTM E
779 or similar test.
STRUCTURAL PERFORMANCE
The air barrier must be rigidly supported to transfer the design wind loads
gusts (negative and positive) safely without tearing, widening of holes at fasteners,
or displacement against adjacent materials. Continuous, persistent lower air pressures acting on joints, such as stack effect
or HVAC fans, can work to loosen some
adhered membranes and tapes.
Figure 2.4 Flow around a building in a boundary layer.
Figure 3. Plan view of roof with contours showing negative pressure distribution. From Leutheusser, H.J., University of Toronto, Department of Mechanical Engineering, TP 604, April 1964, Fig 15. 10.7.
Figure 4.
Summer 2007 29
3. HVAC Fan Pressure: Fan Pressure is
caused by HVAC system pressurization, usually positively, which is fine in
cooling climates but can cause incremental envelope problems to wind and
stack pressures in heating climates.
HVAC engineers tend to do this to attempt to reduce infiltration, and with it
pollution and disruption of the HVAC
system design pressures.
Figure 5 shows each of these pressures on its own, and a combined diagram.
Figure 5.
DURABILITY
Since the air barrier is often inaccessible within the envelope layers, it needs to
last as long as the intended service life of
the assembly.
AIR LEAKAGE THROUGH THE ENVELOPE
Unlike the moisture transport mechanism of diffusion, air pressure differentials
can transport hundreds of times more
water vapor through air leaks in the envelope over the same period of time.3 Air
leaks can be one of three different modes:
• Diffuse flow, such as flow through air
permeable materials.
• Orifice flow, such as flow through a
crack between the window frame and
the wall.
• Channel flow: Channel flow is by far
the most serious from a condensation
standpoint. Air moving through the
building envelope materials can encounter a dewpoint temperature and
can condense within the envelope in a
concentrated manner, wherever those
air leaks may be (Figure 1).
30 Journal of Building Enclosure Design
AIR PRESSURES ON BUILDINGS
There are three major air pressures on
buildings that cause infiltration and exfiltration:
1. Wind Pressure: Wind pressure tends
to pressurize a building positively on the
façade it is hitting, and as the wind goes
around the corner of the building it cavitates and speeds up considerably, creating especially strong negative pressure
at the corners, and less strong negative
pressure on the rest of the building
walls and roof (Figure 2, Figure 3).
2. Stack Pressure: Stack Pressure is
caused by a difference in atmospheric
pressure at the top and bottom of a
building due to the difference in temperature, and therefore the weight of
the columns of air indoors vs. outdoors in the winter, and reversed for
buildings in hot climates with air conditioning indoors. Stack effect in heating
climates can cause infiltration of air at
the bottom of the building and exfiltration at the top, as seen in Figure 4. In
cooling climates, the reverse happens.
CODE REQUIREMENTS
Massachusetts, since 2001 has had air
barrier requirements in the building code.5
Those air barrier code requirements
are summarized as follows:
• A continuous plane of air-tightness
must be traced throughout the building
envelope with all moving joints made
flexible and air-tight;
• The air barrier material in a system
must have an air permeance not to
exceed 0.004 cfm / sf at 0.3” wg (1.57
psf) [0.02 L/s.m2 @ 75 Pa];
• The air barrier “system” must be able
to withstand the maximum positive and
negative air pressure to be placed on
the building and transfer the load to the
structure;
• The air barrier must not displace under
load or displace adjacent materials;
• The air barrier material used must be
durable or maintainable;
• Connections between roof air barrier,
wall air barrier, window frames, door
frames foundations, floors over crawlspaces, and across building joints must
be flexible to withstand thermal, seismic, moisture and creep building
movements; the joint must support the
same air pressures as the air barrier
material without displacement;
• Penetrations through the air barrier
must be made airtight;
• Provide an air barrier between spaces
that have significantly different temperature and/or humidity requirements;
• Lighting fixtures are required to be airtight when installed through the air
barrier;
• To control stack pressure transfer to
the envelope, stairwells, shafts, chutes
and elevator lobbies must be decoupled from the floors they serve by
providing doors that meet air leakage
criteria for exterior doors, or the doors must be gasketed; and
• Functional penetrations through the envelope that are normally inoperative, such as elevator shaft louvers and atrium smoke
exhaust systems must be dampered with airtight motorized
dampers connected to the fire alarm system to open on call
and fail in the open position.
Of course there are many products formulated to qualify as air
barriers materials. Some of these, as well as specifications, technical help, etc. can be found at www.airbarrier.org.
LOCATION OF THE AIR BARRIER
The air barrier, unlike the vapor retarder (since its function is
to stop air, not control diffusion) can be located anywhere in the
envelope assembly. It can be on the warm in winter side, in
which case it can also control diffusion and would be a low-perm
vapor barrier material. In that case, it is called an air/vapor barrier. Or it can be on the cold side of the wall, in which case it
should be vapor permeable (5-10 perms or greater). Vapor retarders, when used, must always be placed on the high vapor
pressure side of the insulation. 6 For examples of this, visit
www.mass.gov and search “energy code details”.
(Figure 6, Figure 7 and Figure 8) of air barrier system design continuity and structural integrity, taken from the reference
details published by Massachusetts at www.state.ma.us/bbrs/energy.htm.
Air barriers on the exterior side of the insulation: Air barriers
that are subject to thermal changes are more difficult to keep airtight for the life of the building, because of the integrity of the
jointing tape or sealant over a long period of time. The best tapes
for non-moving joints are:
• Silicone (extruded) bedded in wet silicone;
• Wet silicone reinforced with fiberglass mesh;
• Other fluid-applied elastomeric air barriers products, reinforced with fiberglass mesh; and
• Self-adhering modified bitumen with surface properly primed.
In short, if you can avoid the above, the building will be more
durable, longer.
ROOF AIR BARRIERS
The roof membrane can be considered an air barrier since it
is designed to withstand wind loads, if it is fully adhered. Mechanically fastened and ballasted roof systems, because they displace
and momentarily billow or pump building air into the system, do
not perform the required functions of containing air without displacement. In those cases, another air barrier must be provided
in the system. Either a self-adhering modified bitumen air and
vapor barrier on the inboard side of the roof system (interior
conditions and weather-dependent), or two layers of asphalt felt
mopped down with asphalt, or similar air barrier. Those layers
must be designed to withstand design wind loads without displacement. One of the vital concepts, that of continuity with the
wall air barrier, is paramount. A pre-construction conference on
roofing must include a discussion of the connection between the
roof air barrier and the wall air barrier, and the sequence of making that air-tight and flexible connection. It is also important to
ensure compatibility between materials coming together. Penetrations into roof systems such as ducts, vents, roof drains, etc.
must be dealt with perhaps using spray polyurethane foam or
other sealant, or membranes to air-tighten those penetrations at
the selected air barrier layer.
CASE STUDY
Worcester Trial Court, Worcester, MA
Architect: Shepley Bulfinch Richardson and Abbott
The Worcester Trial Court in Worcester Massachusetts is designed to house 27 courtrooms for Superior, District, Juvenile,
Housing, Probate and Family Courts. There are five floors and
penthouse, totaling 427,000 square feet. It is the first CM at risk
project undertaken by the Division of Capital Asset Management
in the Commonwealth of Massachusetts.
Worcester Trial Court is a steel framed structure with concrete floors, brick, cast stone, EIFS and glass walls with a series of
high sloped and low slope roof areas. The high sloped roofs are
standing seam lead coated copper panels with cornices, soffits
and internal gutters. The low sloped roof areas consist of three
roof types, a TPO fully adhered membrane, built-up roofing
membrane installed in hot asphalt and a modified bitumen roofing
system in cold adhesive. These roofs are terminated at metal
edges, parapets and rising walls with internal drains and scuppers.
All of the roofs incorporate high levels of insulation, six inches of
extruded polystyrene insulation or polyisocyanurate insulation.
Figure 6 - The Worcester Trial Court under construction with finished metal roofing in
place.
Figure 7 - Structure, vapor retarder, insulation and decking under construction.
Summer 2007 31
is examined to illustrate the connections required for continuity
of the air barrier.
Figure 6, Figure 7, Figure 8, Figure 9 and Figure 10 are
sample photographs of the conditions during construction
Figure 8 - Detail of sloped roof edge.
Figure 9 - Modified detail of diagonal wall meeting underside of metal deck. Note foam
filling flutes of deck.
CONCLUSION
An air barrier system is an essential component of the building
envelope of fully heated and/or conditioned buildings, so that
those buildings’ mechanical systems can perform as intended, and
the enclosure be durable and sustainable. Building codes should
require air barriers systems, and building designers and builders
should be aware of the consequences of ignoring building airtightness.
This article reprinted, with permission, from the Proceedings of
the RCI 22nd International Convention, Orlando, Florida, March 1-6,
2007. ©2007 RCI. All rights reserved.
Wagdy Anis, FAIA, LEED AP is a principal focuses on building science
and building enclosure design excellence with Shepley Bulfinch
Richardson and Abbott, architects, planners and interior designers, an
international practice based in Boston, MA, USA, and is the chairman
of BETEC, a council of the National Institute of Building Sciences.
William Waterston, AIA, RRC is a Senior Associate and Project Manager for Wiss, Janney, Elster Associates, Inc. in their Boston area office. He has experience in project management, construction document preparation, and specification writing. With over 15 years of
specific experience in roofing products and systems, his knowledge of
modified and built-up roofing systems is extensive. Waterston’s work
at WJE includes the investigation, evaluation, and design of roofing
and waterproofing systems. He is an active member of the Building
Envelope Committee of the Boston Society of Architects.
BIBLIOGRAPHY
Air Leakage in Buildings, Wilson, A.G. CBD 23, NRC 1961
Wind on Buildings, Dalgliesh, W.A., Boyd, D.W., CBD 28,
NRC 1962
Wind Pressure on Buildings, Dalgliesh, W.A., Schriever,
W.R., CBD 34, NRC 1962
Control of Air Leakage is Important, Garden, G. K. CBD
72, NRC 1965
Stack Effect in Buildings, Wilson, A.G., Tamura, G.T
Figure 10 - Air barrier on wall at roof edge, extends under cornice.
Photos from the construction of the roofing systems are included with attention to the terminations and integration with
the air barrier systems. References are made to the construction
details. Locations examined are the wall/roof intersection at the
parapet walls, the roof edge and the rising wall locations. The
sloped roof to the skylight construction will be shown. Intersection of the air barrier wall against the underside of the metal deck
32 Journal of Building Enclosure Design
REFERENCES
1. A Guide for the Wind Design of Mechanically Attached
Flexible Membrane Roofs: NRC-IRC-47652E.
2. Investigation of the Impact of Commercial Building Envelope Airtightness on HVAC Energy Use 2005, NISTIR
7238, by Emmerich, S., McDowell, T., and Anis, W.
3. The difference between a vapor barrier and an air barrier:
Quirouette, R.L. http://irc.nrc-cnrc.gc.ca/pubs/bpn/
54_e.pdf.
4. Figures 2 and 3: Building Science for a Cold Climate: NRC,
Hutcheon, N., Handegord, G.
5. 780 CMR 1304.3.
6. ASHRAE Handbook of Fundamentals 2005.
Feature
Curtain Wall Mock-up Testing
By Henry Taylor, Architectural Testing, Inc.
MOST OF US CAN QUICKLY IDENTIFY
the TransAmerica Building in San Francisco
by its pyramidal shape, the John Hancock
building in Chicago by its skeletal frame design, and New York City’s Chrysler Building
by the art deco crown. Further, Frank
Lloyd Wright’s Falling Waters nestled over a
stream in western Pennsylvania is equally
identifiable.
These structures are identified by the
distinctive characteristics of the exterior
walls. Importantly these same exterior
walls are the primary barrier between nature’s outside elements and the interior environment. It is the performance of these
walls that we will discuss here.
The walls of many residential and lowrise buildings rely on conventional, proven
construction methods without extensive
pre-construction testing to validate the ability of the walls to resist air infiltration, water
penetration and structural loads. Often, wall
performance is compromised because of
the cost of performing quality assurance,
pre-construction tests. Instead, the building
owner often relies on the reputation of the
material suppliers and the represented performance of their products coupled with
the building contractor’s assurance of the integrity of the finished building.
However, high-rise (skyscrapers) and
other monumental buildings require millions of dollars to construct the wall envelope, and that wall system is often—or generally—a unique design of various materials
and components. Therefore the investment
in pre-construction performance qualification tests is financially justified. This testing
process provides an ideal time to examine
transition details between different materials, to further develop unique features and
to train the construction/installation crews
on the proper methods and installation sequence to effect a sound wall installation.
This curtain wall, as it is frequently
called, is exposed to the harshest of nature’s elements: intense sunlight raising surface temperatures to as high as 180ºF
(82.2ºC), extremely cold air temperatures
to 0ºF (-17.8ºC) or colder, hurricane wind
loads with concurrent flying debris, earthquakes and building movement, heat
loss/gain and condensation, noise pollution
and more. Therefore these unique curtain
walls require sufficient scrutiny to validate
long term performance before, during and
after these extreme events.
Historically the project architect accepted total responsibility for all of the
project details from concept through completion. The architect would develop the
signature building by considering the
owner’s perception, project costs, the intended use or function, the surrounding
area, etc. He/she would follow through by
providing a performance specification,
quality assurance procedures, shop drawing review and approvals, and the many diverse details involved in creating a new,
monumental structure. An important function was the hand-in-hand research the architect would cultivate with the reputable
suppliers and contractors to assure the results that the owner expected.
Today the architect has been removed
from many of these functions and responsibilities. The architect often merely provides concept drawings of many aspects of
the project which are then turned over to
the construction manager who pushes the
responsibility down the chain to the subcontractors, suppliers and installers. Now,
more than ever before, the architect must
rely on the project specifications for prequalification mock-up testing and quality
assurance during the installation process
with the hope that the CM does not valueengineer this important function out of the
project.
A full-service independent testing laboratory can provide the services necessary
to evaluate the performance of these complex wall systems pursuant to the specifications and desires of the architect. Whoever
is responsible for evaluating the mock-up
performance should coordinate the mockup construction and testing protocol that
provides assurance that the intent of the
Curtain wall mock-up being finalized and inspected prior
to initiating the test sequence.
View of curtain wall mock-up from inside the test chamber
prior to testing.
Sloped glass wall system being prepared for testing.
Interior detailed view of jamb anchor into concrete substrate.
Summer 2007 33
Mock-up composed of ribbon windows and natural stone.
Three story mock-up being prepared for air infiltration tare procedure.
Roof soffit and support capping a curtain wall
mock-up with many angles, transitions, and materials.
Dynamic water infiltration test using an aircraft
engine on a 55 feet high mock-up.
34 Journal of Building Enclosure Design
architect’s specifications and quality assurance program are met.
A basic mock-up test will include air infiltration, static and dynamic water penetration, and design load and structural overload tests (typically 1.5 times the design
load). Generally several optional tests are
added to this basic sequence. For example
a repeat of the air infiltration test and the
static and dynamic water penetration tests
are conducted after the mock-up has been
stressed by the design load test. Similarly,
building movement caused by the live and
dead loads expected on the structure is
often simulated on the mock-up after which
these same tests are again repeated.
Other critical tests include the thermal
movement caused by extreme temperature
changes of the building materials. A curtain
wall is composed of many different materials with a wide range of expansion created
by temperature changes thereby creating
challenges for maintaining air and water
seals. Often the mock-up is enclosed within
an insulated chamber where air temperatures are cycled from the low design temperature (say 0ºF, -17.8ºC) to the expected
high surface temperatures caused by infrared heat from the sun (up to 180ºF,
82.2ºC). Then a repeat of the air and water
tests are generally conducted to evaluate
performance after several temperature cycles which represent environmental exposure and stress.
Accurate heat loss (thermal transmittance or u-value) tests are, of necessity,
performed in a sophisticated chamber; during this same test process an accurate Condensation Resistance Factor (CRF) can, and
should, be obtained. Knowledge of the uvalue is important for specifying HVAC systems, but the American Architectural Manufacturers Association has a document
AAMA 507 that has proven to be a valuable
tool to predict thermal performance of curtain wall systems.
Catastrophic failure of ribbon window during testing.
Noise pollution has created increasing
demand for the knowledge of acoustical
performance of the building’s wall system.
Highway, aircraft and other industrial noises can be dampened by a thorough
knowledge of the specific noise source
coupled with the products that can attenuate the specific frequencies generated.
An OITC (Outdoor-Indoor Transmission
Class) rating of the components will be a
good indicator for selection of windows
and some other components. Increasingly,
demands for acoustical testing of the curtain wall mock-up is being required to
verify the anticipated performance and to
help identify sources of leakage so improvements can be included during the installation of the wall system on the project.
After mock-up testing has been completed, the results accepted and the final
mock-up detail has been properly documented, it is equally important to assure
that the final curtain wall fabrication and
installation duplicate the approved design
resulting from the testing program. Often
your testing agency can provide the consulting necessary to follow through with
this important function, inspecting the installation and performing in situ tests to
further validate that the “delivered” building will perform as expected.
Consultation with the engineers and
technicians of a competent, independent,
and experienced testing laboratory will
provide the information necessary to help
assure that the monumental building
will perform as expected for many years
without extensive and unnecessary
maintenance.
Henry Taylor is president and founder of Architectural Testing, Inc. They have eight laboratory locations across the United States
with over 700 feet of test wall dedicated to
mock up testing.
Uniform load testing of roof structure of a sunroom using sandbags.
Feature
Perimeter Joints
What’s the right thing to do at the joint between the floor
assembly and an exterior wall?
By David W. Altenhofer, AIA, RMJM Hillier
UNDERSTANDING THE ISSUE
The joint between the floor assembly and the exterior wall faces
many challenges: to limit the spread of flames and smoke, control air
movement, contain the spread of contaminants and provide acoustic
isolation. When the joint is required to be fire-rated, then tested assemblies are required which further complicate the decision because
of ambiguities in the code, conflicting manufacturer’s data, the lack of
reliable test methods and inconsistent interpretations by local code
authorities. Selecting the proper system for this joint is not at all clear
and no single easy response is available. Also, each architect and engineer must make their own professional judgment. I am not suggesting
that this paper establishes a guideline, let alone a standard. Instead,
the paper is meant to point out the performance issues, suggest solutions and make recommendations for future testing.
The joint configuration occurs in several categories: rated walls intersecting rated floor assemblies, non-rated walls intersecting rated
floor assemblies, rated walls intersecting non-rated floor assemblies
and finally non-rated walls intersecting non-rated floor assemblies.
Each of these four categories can be further broken down into subcategories based on if the wall spans from floor-to-underside of slab
above or if the wall spans past the outside edge of the slab (curtain
wall). One of the more problematic categories is when curtain wall
spans past the edge of a rated floor assembly and will be the focus of
this paper. For the purposes of this paper, only non-combustible commercial construction with concrete floor slabs will be considered. Systems that require a gypsum board, plaster or other ceiling membrane
to provide a rated floor/ceiling assembly are not included. I am presenting this paper not as a code or fire safety expert but as a practicing architect who must face these decisions almost daily. The article is
based on the results of material found using normal research practices, for example Google searches, code reviews and manufacturer’s
literature.
WHY SHOULD AN ALUMINUM FRAMED CURTAIN WALL BE CONSIDERED
A DIFFERENT CONDITION?
Much of the confusion regarding the wall-to-floor joint centers
around one particular type of exterior wall, specifically curtain wall
framed with aluminum extrusions and infilled with glass. Aluminum
framed glass curtain wall systems do not otherwise receive special attention in the code. They are typically allowed as a non-rated, noncombustible assembly and they do not appear to carry any special risk
of failure when compared to other non-rated, non-combustible exterior wall assemblies.
The risk of the wall and glass failing before the time rating of the
test is frequently touted as a reason to treat these walls differently.
However, protecting against flames jumping from floor to floor is covered in other portions of the code. Currently by code it would be
36 Journal of Building Enclosure Design
possible to have many other exterior wall assemblies and these walls
would be allowed to have windows that extend to the underside of
the floor slab and start again at the top of the floor slab. I cannot conclude that the interruption of a floor slab substantially increases protection against the jumping of flame to the next floor and likewise find
it is not reasonable to focus differently on aluminum framed curtain
walls.
CODE REQUIREMENTS
Limiting the passage of flame and the products of combustion is a
well understood requirement in the protection of life and property.
Protecting the inevitable gap at the intersection of the exterior wall
and floor is no exception. The concern about the “void” between the
floor and exterior wall construction is because this gap, to quote IBC
2006 Commentary, “clearly requires sealing to prevent the spread of
flames and products of combustion between adjacent floors”. Fulfillment
of that requirement at this particular location in a manner that is acceptable to both the spirit and letter of the code becomes somewhat
confusing because of the limitations of testing methods and because
exterior walls are frequently not required to be a fire-resistive rated
assembly. Additionally, the merging of the three major U.S. code writing bodies into the ICC, the evolution of the IBC since 2000 and information provided by fire stopping manufacturers have left many architects, engineers and even code authorities unclear.
From the code, it appears reasonable to assume sealing of the
joint at the exterior wall/floor interface is an independent issue from
protecting against the spread of fire vertically up the building resulting
from the heat of the fire breaking out glass and then leaping to the
next floor. In IBC 704.9 “Vertical Separation of Openings” the requirements for protection against this occurrence (except in low-rise
buildings) are rated spandrel, rated horizontal flame barriers or fully
sprinklering the building. There are no limits placed on the size, placement or rating of fenestration; in other words, the entire wall could
be made of glass and would still comply with 704.9, provided the
building is fully sprinklered. I have not found evidence for a significant
number of losses resulting from flames jumping floors in sprinklered
buildings. This is significant because it seems logical not to consider
how long glass, or even the non-rated wall assembly itself will stay in
place in the selection and detailing of the joint sealer because that
safety precaution is addressed through requirements of 704.9.
At this time the model code (2006 International Building Code will
be used for the sake of this article) allows two test methods for the
exterior curtain wall/floor intersection (Section 713.4). The first,
ASTM E119, tests the materials essentially independent of the surrounding construction. The second, ASTM E2307-04 “Standard Test
Method for Determining Fire Resistance of Perimeter Fire Barrier
Systems Using Intermediate-Scale, Multi-story Test Apparatus”
attempts to recreate test conditions more similar to in-place field
conditions. E2307 was added to the 2006 IBC and there is a chance it
may supersede E119 in future editions based on the commentary and
the long history of proposed code revisions, many of which are sponsored by firestopping manufacturers. The two test methods results in
dramatically different system designs, although the materials are similar. It is important to note the slightly different wording of the code
for each. For E119 the code requires materials or systems capable of
preventing the passage of flame and hot gases “where subjected to
ASTM E119 time-temperature conditions”. For E2307 the requirement is, “installed as tested in accordance with ASTM E 2307”.
The question is, should architects and engineers require systems
which comply with E2307 or is E119 sufficient? It appears that the
two methods differ substantially in that the E119 method allows use
of materials that are proven by test method to “generically” resist the
passage of flames and smoke but have not been tested for the exact
configuration of the final use. E2307 attempts to create a more realistic test configuration, however, by doing so it now creates a requirement for the exterior wall to stay in place for a prescribed period of
time, which is over and above the code requirement for that wall.
The International Firestop Council claims that “Designing the wall
to keep the firestop system in place for the rated period of the floor
is an obvious necessity” to meet the “letter of the law” of the building
codes, which is directly in conflict with my interpretation of the code
regarding E119. E2307 also appears to add requirements for protection against flames jumping from floor to floor which is properly described elsewhere in the code as discussed above. I do not find the
extra requirements of E2307 over E119 to be logically applied or
consistent with other areas of the code. The logic of using materials
tested “generically” for the resistance to the passage of smoke and
flames does seem to have other applications in the code, such as for
penetrations of nonfire-resistance–rated assemblies (Section 712.4.2).
Therefore, I conclude that using materials or systems properly installed and tested in compliance with E119 as acceptable to protect
the fire-resistant joint between a rated floor and an unrated curtain
wall. Architects and engineers should also review their approach early
with the code Authorities Having Jurisdiction (AHJ) as they ultimately
have to approve the joint system. Finally, each architect and engineer
will have to decide for themselves which approach suits the particular
requirements for each of their projects.
Common to all joints is that they must be able to accommodate differential movement between the wall and the floor. Finally, the joint
system is frequently installed before the building is completely watertight. Therefore, the joint should resist a reasonable period of exposure to sun and moisture without deleterious effect.
To adequately design joints against these performance criteria is
presently difficult because they are not tested against these criteria.
For the time, it is reasonable to make sure that approximately 4 inches (100 mm) of mineral wool or similar non-combustible filling is
stuffed into the joint and well supported from the slab edge. An elastomeric fire-resistant sealant material covering the mineral wool
should be at least 1/4 in. (6 mm) and preferably 1/2 in. (13 mm) thick
to provide for proper two sided sealant adhesion and the ability to
withstand cyclic building movement. Of course, this has to be within
the installation methods prescribed by the approved test.
A MORE APPROPRIATE APPROACH TO TESTING?
In my opinion, it is highly unlikely to find a means to test this
joint for actual performance in a fire. In instances when the code
does not require the exterior wall assembly to remain in place for
any prescribed length of time it is illogical to create a test method
that requires the wall assembly to stay in place for a prescribed
length of time. Performance of the joint to resist flames and
smoke from a fire that does not cause failure of the wall before
the rated time of the floor after aging and cyclic movement of the
joint system is extremely important and not currently covered by
either test method. Additionally, there are many other performance criteria that could genuinely provide additional protection of
ADDITIONAL PERFORMANCE REQUIREMENTS
Beyond the code requirements, the joint between the exterior
wall and the floor slab, no matter how they are joined or rated, must
also perform several other tasks. For nearly all buildings, the joint will
need to perform these tasks continually as compared to the relatively
unlikely event of a fire and therefore are very important to the proper functioning of the building. The joint must provide acoustic isolation between floors and this is particularly true when there is no suspended ceiling.
It is desirable for the joint to stop the movement of air between
floors. This becomes more important if the building is very tall because of the increased pressures resulting from stack-effect. For
buildings utilizing under floor air distribution it is imperative to make
the joint air tight to control air distribution. In buildings with concerns
for the distribution of contaminants such as hospitals or labs, maintaining the perimeter floor joint airtight becomes important.
Summer 2007 37
life and property. A more appropriate test
should be conceptualized as follows:
• If the wall is otherwise allowed by the
building code to have 0 hours fire-resistance rating, the test should not be designed to expect the wall to last as long as
the slab or even some portion thereof. If a
wall falls away or glazing breaks out, as allowed by code under the “Vertical Protection of Openings” section, then there
is no reason to expect the perimeter seal
to continue to perform.
• Attachment of the sealing system should
be to the floor assembly only, since this is
the component whose integrity the seal is
supposed to protect.
• Testing should address anticipated building
movement and the seal should still perform after long term cyclic movement.
• Testing should address the real world
condition of a fire not immediately adjacent to the exterior wall.
• Testing should include a reasonable air
seal performance value after movement.
• Testing should include resistance to deterioration from a short exposure to the
weather to simulate current installation
methods and still meet relevant performance criteria.
Some propose that E2307 should include
sprinklers, which are commonly included in
many buildings, especially those with aluminum and glass curtain wall. I do not subscribe to that theory as fire stopping and joint
protection is part of the passive fire resistance features of a building and other similar
fire stops are not tested with sprinklers. David Altenhofen, AIA CSI CCS is an Associate
Principal and Technical Director of the Philadelphia Office of RMJM Hillier, a 1,000 person international architecture firm. He is active in
the AIA, BETEC and is widely published and lectures frequently at local, national and international events.
REFERENCES
Article from UL regarding current trends.
Glass industry news digest regarding ICC
direction.
International Firestop Council presentation
regarding fire-resistant joints.
Perimeter_Curtain_Wall.ppt
www.ul.com/tca/spring05/
www.usgnn.com/newshearings
38 Journal of Building Enclosure Design
Feature
Rain Screens: The New Standard
AAMA 508-07 Voluntary Test Method and Specification for
Pressure Equalized Rain Screen Wall Cladding Systems
By Jennifer Pollock, Architectural Testing, Inc.
AS THE POPULARITY OF rain screen
cladding systems continues to grow, so
does the need for test methods and performance guidelines for such systems. To
this end, the American Architectural Manufacturers Association (AAMA) has recently
published AAMA 508-07 Voluntary Test
Method and Specification for Pressure
Equalized Rain Screen Wall Cladding Systems.
The new standard quantifies the performance of pressure-equalized rain screen
(PRWC) systems, the most sophisticated
rain screen cladding system. PRWC systems
feature high venting and good drying capabilities, while substantially reducing pressure
differentials that drive water through the
exterior cladding. Ventilation is a built-in
component of the joinery of such systems,
which employ a separate air barrier and
drainage plane to carry incidental water out
of the system. Compartmentalization allows the system to maintain constant pressure and minimize the amount of water that
bypasses the exterior screen.
Before the establishment of the new
AAMA standard, any manufacturer could
claim to have a pressure equalized rain
screen product on the basis of an assumption of perfect air and water barrier, but
there was no recognized way to verify
these claims. Various commercially available
systems relied upon the air barrier and
drainage plane that are commonly provided
by others—not by the manufacturers of the
PRWC systems. Since AAMA 508-07 was
published, manufacturers have been able to
compare the performance of their products
with others on the market without depending solely on the air and water barrier quality.
In general, water leakage is driven by
five forces: kinetic forces, gravity, surface
tension, capillarity and pressure differentials. Any number of these forces can be
acting on water penetrating the building
Figure 1 - Pressure Equalization Cycling Chart.
envelope; the goal of a design is to eliminate
or minimize their effects. Kinetic forces
refer to the horizontal velocity wind-driven
rain drops possess. The momentum can
carry them directly through sufficiently
sized openings into the envelope interior.
The actual rain screen cladding serves to
keep most of this water out of the system.
Gravity, capillarity, and surface tension can
all be combated with appropriately designed flashings or drip edge. Pressure differences between the cladding exterior and
interior generated by mechanical systems,
stack effects, and wind also act to force
water through. Pressure equalized systems
were designed specifically to resist this
mechanism of leakage and is an important
characteristic of the system to be tested.
Basic ASTM and AAMA test methods
make up the bulk of 508-07, including
ASTM E 283 Standard Test Method for Determining Rate of Air Leakage Through Exterior Windows, Curtain Walls, and Doors
Before the establishment of the
new AAMA standard, any
manufacturer could claim to have
a pressure equalized rain screen
product on the basis of an
assumption of perfect air and
water barrier, but there was no
recognized way to verify these
claims.
Under Specified Pressure Differences
Across the Specimen; ASTM E 331 Standard Test Method for Water Penetration of
Exterior Windows, Skylights, Doors, and
Curtain Walls by Uniform Static Air Pressure Difference; ASTM E 1233 Standard
Test Method for Structural Performance of
Summer 2007 39
Exterior Windows, Curtain Walls, and
Doors by Cyclic Static Air Pressure Differentials, and AAMA 501.1, Standard Test
Method for Water Penetration of Windows,
Curtain Walls, and Doors Using Dynamic
Pressure.
AAMA 508-07 actually takes into account imperfections that commonly occur
during the installation of the air/water barrier system. The Air Barrier Association of
America recommends a 0.15L/s/m2 air leakage rate, but the new standard increases
this rate to 0.6 L/s/m2 ± 10 percent to account for the anticipated field defects in the
as-built conditions of the air and water barrier. The ASTM E 283 Air Leakage test is
performed at a specified pressure differential of 75 Pa (1.57 psf), which is roughly
equivalent to a 11 m/s (25 mph) wind velocity. The test is completed both prior to
and after the rain screen cladding is installed
over the air/water barrier. The purpose of
the air leakage test is not to validate the
performance of the air/water barrier but
rather to determine what impact the installation of the rain screen cladding has on the
overall air leakage of the composite assembly. Testing performed by Architectural
Testing has indicate that the air leakage of
the assembly can change as much as 10 percent when the cladding is installed.
The ability of pressure equalized rain
screen cladding to control water intrusion is
determined by observing the amount of
water that contacts the air/water barrier.
The test assembly is subjected to both static water and dynamic water tests (ASTM E
331 and AAMA 501.1, respectively) and the
amount of water penetrating the rain
screen is observed and recorded after each
test. The standard also requires documentation of the nature of the water penetration, such as specific observations on the
quantity and location of continuous streaming of water and/or misting occurring on the
air/barrier surface, and/or water damming
in any channels. Accredited laboratories
which perform the test must record and
document in the report the amount of
water penetrating the rain screen and contacting the air/water barrier; the AAMA 508
test limits the amount of water that contacts the air/water barrier to five percent of
the total wall area. The five percent criterion was established by the task group based
on the resulting data from research testing.
In addition to limiting the water contacting
the air/water barrier, the standard also prohibits the accumulation of water damming
in the system.
Pressure equalized rain screen claddings
rely on the capability of the system to
achieve equilibrium when wind and other
natural forces create pressure changes on
the exterior of the cladding. Since this is the
primary mechanism used to control water
penetration, the standard also requires testing to validate the pressure equalization
characteristics of the wall system. Utilizing
the ASTM E 1233 test method, cavity pressure readings are recorded in three locations—on the exterior and in two interior
chambers—and plotted over time to determine the pressure equalization performance. The recorded pressure data is then
presented graphically to determine the
pressure difference between the interior
and exterior chambers as well as the lag
time for equalization (Figure 1). AAMA
508 restricts lag time to 0.08 seconds and
the interior pressure to at least 50 percent
of the exterior pressure.
All wall cladding, whether pressure
equalized or not, is subjected to some wind
loading. Structural testing per ASTM E 330
is included in the AAMA 508 specification as
an option to validate the structural characteristics of the wall system. The specification does not attempt to specify a reduction
factor for pressure equalized cladding however some industry experts suggest that a
properly designed and constructed rain
screen wall cladding may have to withstand
as much as 75 percent of the full design
pressure due to rapid changes in outside air
pressure.
The AAMA Task Group has worked
hard to ensure fair and accurate testing
methods with meaningful performance requirements, but AAMA 508-07 is only the
beginning of that work. Also under development are voluntary standards for drained
and back-ventilated rain screen wall
cladding systems and perhaps barrier wall
systems.
Jennifer Pollock is a project engineer with Architectural Testing, Inc., and is a graduate of
Lafayette College with a degree in Mechanical
Engineering. She is a member of the AAMA
working task group and has performed numerous tests using the AAMA 508 test methods
and specification.
40 Journal of Building Enclosure Design
Feature
Characterizing Air Leakage
in Large Buildings: Part I
By Terry Brennan and Michael Clarkin, Camroden Associates Inc.
THE FAN PRESSURIZATION TEST
Pressure testing to determine the air tightness of a building’s enclosure is conceptually simple. A variable speed fan is used to either
exhaust air from a building or supply air to a building. This changes
the building’s air pressure relative to the outdoors—hence the
name Pressure Testing. To some, this name may be a little confusing
because most tests are done by exhausting building air.
When a mass of air is exhausted or supplied to a building, the indoor/outdoor pressure relationship changes until the same mass of
air enters or exits the building through leaks in the building enclosure. Once this mass balance is reached, the induced pressure difference stabilizes. The magnitude of the pressure difference between inside and outside depends on the size and shape of the leaks
in the building. The smaller the leaks the greater the pressure difference has to be to reach this balance.
Measuring the two variables—the air flow rates and the induced
air pressure differences—provides data that can be used to characterize the building’s air tightness. The quality of the resulting data
depends on how well these two variables are measured. This is
where the conceptual simplicity of the test meets real world complexity. Wind, occupants, equipment limitations, and the skill and
knowledge of the person doing the test impact the test’s overall accuracy.
WHY PRESSURE TEST A BUILDING?
Besides having fun doing weird things in buildings if you are a
building science geek, or making some money if you are a businessperson, there are many reasons for conducting fan pressurization tests, such as:
• To determine whether a building enclosure (or a zone within a
building) meets tightness specifications (Potter 2007). Airtightness may be specified to conserve energy (Emmerich 2007) or
to reduce water vapor migration (Brennan 2002).
• To compare the tightness of a building to other tested buildings
(Emmerich 2007).
• To determine whether air pressure control can reasonably be
expected to solve a problem in an existing building. For example
pressurizing wall cavities to prevent the entry of hot, humid outdoor air or depressurizing a crawlspace to prevent the entry of
radon-laden air (Brennan 1997).
• To develop a “calibrated” airflow model of an existing building.
Airflow modeling software (example, CONTAM) can be used to
predict the effect of changes in the enclosure or mechanical systems on airflows through the building. Such a model can be tested against measured airflow and induced pressure data.
If the test is being conducted to compare the results to a target
airtightness, as the British Part L energy code requires (Potter
Figure 1 - A
calibrated
blower door.
Figure 2 - Multiple blower
doors used in buildings with
leakage areas too large for a
single blower door.
2007), or to compare the building airtightness to other buildings,
specific details of the test must be standardized. Weather conditions, the state of windows and doors, treatment of intentional
HVAC openings through the building shell, and the location and setup of test fan equipment must be considered.
You will need to carefully measure air flows and pressure differences and conduct uncertainty analysis to ensure the accuracy of
the result. There are a number of protocols that can be
followed in conducting the test:
• The British Air Tightness Testing and Measurement Association
(ATTMA) Standard 1: Measuring Air Permeability of Building Envelopes (contains guidance for large buildings);
• CGSB 149.15-96 Determination of the Overall Envelope
Summer 2007 41
Figure 3 - Infiltec G-54 trailer mounted calibrated blower for testing large buildings.
Figure 4 - Measuring total exhaust flows by summing flow through exhaust grilles
(NOTE: This misses air leaks in the ductwork).
Airtightness of Buildings by the Fan Pressurization Method Using
the Buildings Air Handling Systems (contains guidance for large
buildings);
• E 779 – 03 Standard Test Method for Determining Air Leakage
Rate by Fan Pressurization (does not specifically address large
buildings); and
• E 1827 – 96 (Reapproved 2002) Standard Test Methods for Determining Airtightness of Buildings Using an Orifice Blower Door
(does not specifically address large buildings).
If, however, you want to know how many cubic feet per minute
of exhaust air it would take to depressurize a crawlspace by 4 Pascals, the test would need to be conducted differently and the results
are likely to be used to design an intervention in a building related
problem. There are no published protocols for conducting a diagnostic test of this kind.
This article focuses on pressure testing the entire enclosure of a
large building (“large” meaning “not single family residences”). Most
of the building tightness data collected in the United States has been
for single family residences. A much smaller number of other building types have been tested. For non-residential buildings tightness
data has been reported for low-rise, mid-rise and high-rise buildings: for offices, banks, restaurants, food markets, theaters, schools,
warehouses, rowhouses and apartment buildings. They have ranged
in size from several thousand to several hundred thousand square
feet. Many of these buildings present issues that do not occur while
pressure testing single family buildings (Emmerich 2007).
42 Journal of Building Enclosure Design
PLANNING THE TEST
The purpose of the test, how you are going to conduct it, and
what equipment you will use should be well understood and
planned well before going into the field. For example, are you going
to use a blower door, the building’s air handler or some other
method of providing the air flow needed for the test? Where are
you going to measure the pressure differences and with what instruments? Not that the plan won’t change once it encounters the
reality of field measurements, but come prepared or failure is likely.
The purpose of the test determines how much of the building
you are going to test. To determine if the building meets airtightness
specifications the entire exterior shell of a building—defined by the
thermal or air pressure boundary of the building would be tested.
For other purposes a smaller enclosure within a building may be
tested (example, a special use area like a swimming pool or a fruit
ripening room). In apartment buildings air sealing each apartment
reduces transport of air contaminants and odors to neighboring
units, reduces accidental outdoor airflows through the building and
improves the distribution of intentional ventilation air. In this case it
may be as important to pressure test each apartment as the entire
building enclosure.
Collect background information. You need information on the
building itself—the enclosure and the HVAC systems. Architectural
and mechanical drawings are very helpful. The people who maintain
the building, the HVAC equipment and controls are a wealth of information. They are needed on the day of the test to answer questions, open doors and set the HVAC systems to the state you would
like during the testing (without setting off fire alarms or sprinklers,
freezing coils or otherwise damaging equipment or controls). It is
best to schedule the test when the fewest people are likely to be in
the building opening doors and windows, turning exhaust fans on
and off, or doing other things that interfere with your test.
Identify the pressure boundaries of the zone to be tested. The
pressure boundaries may be well defined and implemented. Possibly they were not clearly defined in the design documents during
the design of the building. The location of the actual pressure
boundary can be determined during a pressure test by making pressure drop measurements across each layer of the enclosure. This is
an advanced topic and is not covered in this article. When the
boundaries of the zones to be
tested have been identified, the
surface area of the enclosing
walls, ceilings and floors and the
enclosed volume can be calculated. This information will be needed so the results of the test can be
normalized. Normalizing leakage
to the surface area of the enclosure allows comparison to target
tightness levels or to the normalized tightness of other buildings.
Get an understanding of the
HVAC systems. Locate each exhaust outlet and outdoor air inlet.
Locate each air handler. Trace
supply and return ducts and
Figure 5 - Measuring air flow through an outdoor
plenums. Identify outlets, inlets, air duct by pitot tube traverse.
ductwork and air handling equipment that breaches the boundaries of a test zone. Plan to air seal the HVAC openings that will
compromise the test enclosure. The HVAC inventory may also be
useful if it turns out that using the ventilation equipment in the
building is the best way to pressure test the enclosure.
Estimate the amount of air flow that will be needed to achieve
the required pressure difference. An estimate can be made by calculating the area of the enclosure and multiplying that area by
measured or target normalized leakage rates for buildings of the
type under consideration (ATTMA 2007, CGSB 1996). An on-line
calculator for estimating the amount of airflow needed to pressure
test a building can be found at www.infiltec.com/inf-ukstd.htm.
Determine how the airflows will be provided and measured—see
the next section.
MAKING THE TEST
On the day of the test you will need to be able to close all the
intentional openings in the enclosure, open all the interior doors
and turn off all the ventilation equipment. In many buildings the
buildings and grounds personnel will be needed to get these things
done. An HVAC controls contractor may be needed to turn off
the ventilation system.
You will also have to prepare the building:
If the whole building is one test zone
• Close exterior doors and windows
• Open interior doors
If the test zone is a portion of the whole building
• Close exterior doors and windows
• Isolate test zone from surrounding building
• Close doors
• Tape off supply diffusers and return grilles that connect to
ducts or equipment outside the test zone
• Determine whether adjacent zones should be open to outdoors or closed
• Close outdoor air intakes and exhaust outlets
• Dampers
• Gravity dampers
• Plastic, foam board and tape
MEASURING AIRFLOW
There are three basic strategies for providing known airflow
rates to depressurize or pressurize the building:
• Blower doors: variable speed, calibrated blower doors are
available from two U.S. companies (the Energy Conservatory
and Infiltec) and one Canadian company (Retrotec). Blower
doors are available in a range from 5000 to 8000 cfm. Airflow
through blower doors is easily and accurately measured with
these units. They are easy to install in a door opening. With a
little effort and creativity they can be installed in windows, access hatches or more unusual openings. Multiple blower doors
can be used on one building to achieve higher airflows and to
distribute the induced pressure differences throughout a building. Distributing the air pressure becomes more important as
the size and the number of rooms and floors in a building increase. Figure 1 shows a photo of a single blower door used
in a research project on unplanned airflows in small commercial buildings in New York State (NYSERDA 2006). Figure 2
shows two blower doors being used to test a movie theater in
the same project.
• Trailer mounted fans: Infiltec manufactures a trailer mounted calibrated, variable speed fan that produces flows between 20,000
and 60,000 cfm. This unit is ideally suited for large buildings with
few interior floors or partitions. Problems producing uniform indoor/outdoor pressure differences can occur in more complex
buildings. For example, consider a trailer mounted fan depressurizing the first floor of a six story building, that has two fire
egress stairwells open into the lobby. All the air depressurizing
the top five floors must be drawn through the open stairwell
doors. The first floor may be depressurized to a significantly
greater extent than the upper floors because the stairwell doors
may form a bottle neck, creating a two or three zone problem.
Additional smaller fans depressurizing the upper floors using
windows or rooftop access can be used to even out the depressurization.
Besides the fabled Super Sucker (used for research purposes at
the National Research Council of Canada), currently there is one
trailer mounted fan in North America owned by Jeff Knutson at
A. A. Exteriors in Wisconsin. One interesting aspect of this fan is
that it is powered by a gasoline engine rather than an electric
motor. This makes the unit more flexible than would be the case
Figure 6 - Temporary ductwork on outdoor air intake allows pitot tube traverse.
Figure 7 - Fan powered capture hood measuring flow from a rooftop exhaust fan. This
method provides good accuracy but is limited to flows equal to or less than the flow of the
calibrated fan. Photo courtesy of CDH Energy Corporation and New York State Energy
Research and Development Authority.
Summer 2007 43
if a twenty horse power electric motor
was used to power the fan. You don’t
exactly just plug that big an electric
motor into the nearest outlet. Figure 3
shows a photo of the trailer mounted
G54 being used to pressure test an
810,000 square foot warehouse. The
G54 is ideal for testing large open buildings. Accurate flows are easily measured. Distributing the pressure differences across the enclosure surfaces is
not hampered by internal partitions and
floors.
• The ventilation equipment in the building (exhaust or outdoor air flows) can
be used to pressurize or depressurize
the building. In the United States during
the late 1980’s and early 1990’s this
technique was used (Persily 1986). The
major advantage of this method is that
the air handling equipment is already at
the building. There are three common
difficulties with this method: measuring
the airflow through ventilation systems
is often time-consuming and tedious;
flow measurements made on air handling equipment that is part of the ventilation system are likely to have greater
44 Journal of Building Enclosure Design
uncertainty than flows measured using a
calibrated fan door or trailer mounted
fan unit (extra effort is required to ensure data quality); there may not be
enough outdoor air or exhaust air capacity to achieve the desired pressure
difference or number of flow-pressure
data pairs to meet the data quality objectives for the test. The only protocol
for pressure testing large buildings using
the building air handlers is the Canadian
standard CGSB 149.15-96. There are
two additional references that are helpful (PECI 2005, Lee 1998). The PECI
document is a protocol developed to be
part of a commissioning guide. The
other document is a Master of Science
Thesis. A number of Test and Balance
guides provide protocols and methods
for measuring outdoor airflow through
air handlers and exhaust fans (ASHRAE
2005, SMACNA 2002). Two research
projects that studied unplanned airflows
in non-residential buildings contain descriptions of additional methods for
measuring airflows through air handlers
and exhaust fans (Cummings 1996a and
1996b, 1997, Henderson 2006). There
are a number of techniques for measuring
airflow:
• Measure the velocity of air in ductwork
traversing multiple locations (e.g. using
pitot tube, hot wire anemometer or
vaned anemometers).
• Measure airflow through a duct using an
orifice (e.g. flow measurement stations
built into the system. NOTE: flow station accuracy should be validated using
one of the other flow measurement
methods).
• Measure airflow through diffusers or exhaust grilles using calibrated flow hoods.
• Measure exhaust or outdoor airflow
through rooftop intakes or exhaust using
a flow compensated shroud and calibrated fan.
Up next issue, Part II: how to measure pressure differences and figuring out what all the
facts and figures actually mean, plus a complete
reference guide for both Part I and Part II of this
series.
Terry Brennan and Michael Clarkin are building
scientists who work at Camroden Associates
Inc. They have been pressure testing buildings
since 1981.
Industry Update
BEC Corner
BOSTON
By Boston-BEC staff
In 2006 The Boston Society of Architects’ Building Enclosure
Council (BEC-Boston) established a sub-committee to develop an
awards program to recognize building enclosure design and construction. After six months of hard work the sub-committee, led by
Wei Lam (Morrison Hershfield Corp.) and Ann Coleman (Wiss, Janney, Elster Associates, Inc.), is proud to announce the first annual
Building Enclosure Design Award. A big thanks to all of the committee members who have contributed their time and knowledge: Alec
Stevens (DMI, inc), Jeff Wade, (Add Inc.), Jonathan Baron (SGA Architecture, Inc.), Richard Panciera (Elkus-Manfredi), Richard Keleher
(BEC-Boston Chair), Keith Yancey (Lam Partners, Inc.), Wagdy Anis
(Shepley Bullfinch) and the folks at BSA.
The competition will consider projects by evaluating aspects of
heat, air, moisture, day lighting control, in-service performance, collaboration and other innovations related to the building enclosure.
Outstanding innovation and excellence in these areas will be the
basis for selecting a winning project and runner-up projects to be
recognized during a BSA/BEC-Boston sponsored event during Build
Boston 2007 (buildboston.com). The intent of the award is to promote best practice, innovation, and a transfer of information and
technology related to building enclosure design.
A distinguished panel of judges from the industry has been selected. They include:
Wagdy Anis FAIA of Shepley Bulfinch Richardson & Abbott; David
Altenhofen AIA of Hillier Architects; Desmond McAuley AIA of
Childs Bertman Tseckares Inc.; Daniel Lemieux AIA of Wiss, Janney,
Elstner Associates, Inc.; Mark Lawton P.Eng. of Morrison Hershfield
Limited; Paul Stoller, Director of Atelier Ten; Chris Benedict R.A.,
Principal of Architecture and Energy Limited; and, Keith Yancey AIA,
P.E. of Lam Partners, Inc.The competition is open to built projects
that conform to the Massachusetts State Commercial Building Code
and were completed after January 1, 2002 and before January 1,
2006. For more information about the competition go to:
www.BEC-Boston.Org.
CHARLESTON
By Nina M. Fair, AIA, CCS, LEED AP
Rodeos are not common occurrences in quaint, historic
Charleston, South Carolina, but on May 11, 2007, BEC-Charleston
hosted a wild and wooly Window Flashing Rodeo! The rodeo was
originally conceived by board member (and director of hair-brained
schemes) Larry Elkin in response to ASTM Call for Papers for their
“Up Against the Wall” Symposium. The Rodeo took on a life of its
own, sweeping up all BEC members, designers, contractors, suppliers and manufacturers in its path.
The event was open to 50+ participants forming 11 teams comprised of local construction professionals and trades-people who
participate in BEC. Each team was provided with a standardized wall
mock-up with a rough opening and a nail-flange window. The teams
46 Journal of Building Enclosure Design
were required to develop a design for their window installation in
compliance with requirements set forth in:
• The window manufacturer’s installation instructions;
• The 2003 International Residential Code;
• ASTM E 2112 Standard Practice for Installation of Exterior Windows, Doors and Skylights;
• The weather resistive barrier manufacturer’s instructions; and
• The flashing manufacturer’s instructions.
The teams then installed their windows in accordance with their
designs. Once installed, the assemblies were tested in accordance
with ASTM E 1105 Standard Test Method for Field Determination of
Water Penetration of Installed Exterior Windows, Skylights, Doors
and Curtain Walls by Uniform or Cyclic Static Air Pressure Difference. No exterior cladding or perimeter sealants were installed
therefore the moisture loading on the window/wall interface was
greater than in-service conditions.
Each team reported to the group a summary of their design, installation process and testing results. These results revealed areas of
conflict between the design requirements and some difficulties in implementing the designs. Teams also learned about the benefits of design mock-ups and commissioning to identify design and construction
problems. The anecdotal data provided by this workshop should be
utilized by the publishers of the design and installation documents as
well as the testing standard to influence future.
Recent and upcoming programs for BEC-Charleston are:
• September 2007 Meeting: Sustainability in Masonry Construction by Chris Bupp of Hohmann and Barnard; and
• October 2007 Meeting: Advanced Building Science Seminar by
Jacques Rousseau and Rick Quiroette.
CHARLOTTE
By Phil Kabza, FCSI, CCS, AIA
The Building Enclosure Council-Charlotte is wrapping up its first
year with planning toward an upcoming year of activities that will include a concentrated look at the building enclosure issues of school
construction with our area school district facility leaders, panel discussions featuring construction management staff, and an examination of commercial and institutional roofing issues and options.
In addition to our half-day kickoff event, we have featured presentations on:
• Moisture and mold control in new construction
• Roof/wall and plenum details in thermographic analysis
• Recent litigation issues in building envelope failures
• Introduction to WUFI
We’re looking forward to the coming year and appreciate the
support and information exchange with BEC leaders around the
country.
DALLAS
By George M. Blackburn, AIA, BEC-Dallas Chair
The BEC-Dallas chapter is in its third year of operation and
convenes it’s meetings on the second Tuesday of each month at the
AIA-Dallas office meeting room at 1444 Oak Lawn, Suite 600, Dallas,
Texas 75207. Contact George M. Blackburn, AIA for information on
BEC-Dallas programs and meetings at 972-466-1103. BEC-Dallas is
a sub-committee of AIA-Dallas and Paula Clements, AIA- Dallas Executive Director, has agreed for AIA Dallas to handle all of BEC-Dallas finances, and to publicize all meetings and programs of BEC-Dallas.
The Weatherization Partners (Tyvek) has graciously agreed to pay
the $200 copyright fee to the artist, Deb Gordon, for the BEC-Dallas Logo design copyright.
BEC Dallas was one of the sponsors of the WUFI workshop conducted in Dallas on February 1 and 2, 2007 presented by the Oak
Ridge National Laboratory Building Envelope Program, and received
$1,700 from the Building Science Corp. for the revenue sharing
arrangement.
John Edgar, Senior Technical Service Manager with Sto Corp.
gave an excellent presentation on building enclosure science featuring air and water barriers at the April meeting.
There are some interesting and informative programs on masonry, waterproofing, air barriers, and the Residential Energy Code
scheduled in the coming months. We are also planning on conducting
a fenestration flashing competition in the fall, with contractors, architects and architecture students participating.
HOUSTON
By Andy MacPhillimy, AIA,
LEED AP, Principal Director, Education Studio
BEC Houston has just completed its first year of full successful
programs that range from Green Roofs to “Acoustical Considerations in the Design and Construction of Exterior Walls.” The most
attended was a discussion of “The most Common Design and Construction Issues” related to the building exterior by a panel that included an owner, a general contractor, an architect and roofing and
glazing subcontractors. There was general consensus by panel members that creating a close collaborative working relationship by all
team members was the best at identifying and resolving design and
construction issues early. A WUFI Training session was conducted for
22 people brining a higher level of technical expertise related to
building envelop to the Houston consulting community.
Looking to the next year of programs BEC Houston and the local
ASHREA chapter are working together to conduct joint programs
on such topics as “Interaction of the Envelop and Mechanical System
Design”, Building Envelope, IAQ and Ventilation Effectiveness.
MINNESOTA
By Judd Peterson, AIA, BEC-Minnesota Chair and
Jodelle Senger, AIA, LEED AP
The BEC-Minnesota is excited to announce that the first ever
BEST 1 (Building Enclosure Science and Technology) Symposium to
be held in the United States is scheduled for June, 2008. Mark your
calendars! This two day symposium will be held at the
Minneapolis Convention Center and BEC-Minnesota will be the local
hosts. BEC-Minnesota is working with other state BEC chapters,
NIBS, BETEC and AIA to plan and fund this exciting event. This
American symposium will take place on a bi-annual basis, alternating
years with the Canadian Building Science & Technology Conference.
The BEST 1 Symposium will offer two educational tracks and sixteen
individual sessions. One track will address building health issues:
Bugs, Mold, and Rot IV. The other track will focus on energy efficiency and new technologies: Energy Efficiency in Buildings. Abstracts of
submitted papers are currently being reviewed and certain, selected
papers will be assigned and presented at sessions during the symposium. Additional information can be found on the BETEC website.
BEC-Minnesota will soon host a webpage on the AIA Minnesota
website with symposium-related links and additional information.
In addition to planning the BEST 1 Symposium, we continue to
have our monthly meetings at AIA Minnesota offices. Recent speakers and topics have included Dan Headley of Pella Windows: quality
wood window construction; Wayne Westerbrook of SpecMix/TCC
Materials: mortar and mortar mixes; Reed Gnos of 3M: firesafing in
the exterior envelope; Wilbert Williams of DOW CORNING and Bill
McCann of Chemrex BASF: pros and cons of silicone and
polyurethane sealants; James Flanigan and Matt Breyer of Centria: the
advantages of insulated metal panels; Tom Wickstrom of Spec 7
group: blind side, exterior waterproofing applications. We’ve also
watched a PBS program, titled “Design: e2”, which features six different segments addressing green/sustainable design. These segments
have inspired BEC-Minnesota to research exterior envelope components and systems that not only excel in our Minnesota climate, but
also address the preservation of our natural resources and global environment. The program, Design: e2, was purchased online via
PBS.org and is highly recommended for individual viewing or for inhouse office seminars.
PORTLAND
By Rob Kistler, The Facade Group, LLC
The Portland BEC completed this years presentations in July with
a well attended discussion of Acoustics. We learned how to mitigate
unwanted noise through a curtain wall and other issues that have
arisen with the high rise condominium market. We kicked off this
year with a panel discussion of sustainable practices and the forces
that hold us back from doing more environmentally friendly designs.
Through the year we held presentations on how to design and construct a viable eco-roof and the differing theories of the layering of
the systems. Monitoring systems for either instantaneous feedback
on water infiltration or life cycle building monitoring systems were
presented in the spring followed by a packed room presentation on
fenestration systems from residential face sealed systems through
unitized curtain walls to monolithic point fixed glass walls. September
6 will be our kick off meeting for the next year with a wrap up presentation of a membrane compatibility and adhesion study. We are in
the planning phase of our full day Fall Symposium which this year will
occur Friday, October 26, 2007.
SEATTLE
By David K. Bates, AIA, Olympic Associates Company
Seabec is “cooking with gas.” As we enter our third year, the dust
is settling around the administrative foundations and we formed new
committees to assist the Board of Directors. We have a diverse
membership base of approximately 130 and are formulating a campaign to attract more architects and contractors. We are reaching out
to the University of Washington Schools of Architecture and Building
Construction along with community colleges and other trade groups.
Summer 2007 47
Buyer’s Guide
SEABEC’s Education Committee takes
care of our programming needs and a “virtual” Public Relations Committee has been
started to get the word out to the industry.
A Task Force produced a document to help
guide people through the revised Washington State Condominium Act. After over a
year, this task is completed and we have
posted the work product on our web site,
www.seabec.org.
It is interesting running an organization
that is essentially a “virtual organization” – I
like to think that puts us a little more into
the green arena pushing more bites and less
paper. In the last two years we had programs covering below grade waterproofing,
metal siding, Washington State Energy Code
updates, green roofs, designing for access,
windows, window installations and wraps,
air barriers, bond breakers and sealant, and a
presentation on the Washington State University test facility to name a few.
Over the last year, we have again benefited from the generosity of our member firms
and vendors who generously sponsored
meeting snacks and beverages. 2006/2007
was good. 2007/2008 will be great!
ARCHITECTURAL GLASS
Oldcastle Glass . . . . . . . . . . . . . .26, 27
BUILDING PRODUCTS
Georgia Pacific . . . . .inside front cover
ARCHITECTURAL WINDOWS
Oldcastle Glass . . . . . . . . . . . . . .26, 27
BUILDING SCIENCE &
RESTORATION
CONSULTANTS
Camroden Associates Inc. . . . . . . . .45
Read Jones Christoffersen . . . . . . . .44
ASSOCIATIONS/
INSTITUTIONS
ABAA . . . . . . . . . . . . . . . . . . . . . . . . .7
AISC . . . . . . . . . . . . . . . . . . . . . . . . .35
ASHRAE . . . . . . . . . . . . . . . . . . . . . . .8
Indoor Air Quality
Association . . . . . . . . . . . . . . . . . . . .9
BUILDING ENCLOSURE
CONSULTANTS
Construction Consulting
International . . . . . . . . . . . . . . . . . .40
BUILDING ENVELOPE
ARCHITECTS CONSULTANTS
Conley Design Group Inc. . . . . . . . .48
ENGINEERED CURTAIN WALL &
WINDOW WALL
Oldcastle Glass . . . . . . . . . . . . . .26, 27
ENGINEERS
Sutton-Kennerly . . . . . . . . . . . . . . . .37
ENTRANCE SYSTEMS
SPARE PARTS
Oldcastle Glass . . . . . . . . . . . . . .26, 27
GLASS & GLAZING
Cardinal Glass Industries . . . . . . . . .18
INSULATION
MANUFACTURER
Knauf
Insulation . . . . . . .outside back cover
MANUFACTURER
REFLECTIVE ROOF COATING
LEED COMPLIANT
Karnak Corporation . . . . . . . . . . . . . .6
MASONRY
Mortar Net . . . . . . . . . . . . . . . . . . . .38
RAINSCREEN STUCCO
ASSEMBLY
Stuc-O-Flex International . . . . . . . . .3
ROOFING MANUFACTURER
GAF Materials . . . . . . . . . . . . . . . . . .4
STRUCTURAL ENGINEERING,
DESIGN & CONSULTANTS
WJE . . . . . . . . . . . . . . . . . . . . . . . . . .14
VAPOR BARRIERS
El Dupont Building . . . . . . . . . . . . . .15
WATERPROOFING
Sto Corp . . . . . . . . . .inside back cover
WEATHER BARRIER
Cosella Dorken Products Inc. . . . . .19
48 Journal of Building Enclosure Design
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