Historic Buildings & Green Design
Cape-Wide Historic Preservation Workshop
Adding Insulation to an Older Home:
The good, the bad, and the ugly?
Sally Zimmerman, Historic New England
March 25, 2010
There’s always breaking news on the energy front . . .
and emerging news on green impacts and preservation
www.energycircle.com, March 6, 2010
New York Times, March 18, 2010
What you need to know before you insulate an
older home
What is most often
recommended (and
how these
recommendations are
Why these may not
be right for the older
or historic home
What you can do to
upgrade for energy
savings in an older or
historic home –
A “green” house glossary
Deep energy retrofit
Insulating the interior or exterior
to far exceed current building
and energy codes
Net zero
A net zero, or zero energy,
structure in general is one that
generates more energy than it
uses; it can be, but usually is
not, disconnected from the
power grid. Strictly defined, net
zero structures generate no
carbon emissions
Super-insulation, plus the
addition of renewable energy
sources or other measures to
further reduce the carbon
footprint (passive and active
solar systems, geothermal,
wind power, water use
reduction, landscaping)
Passive home
A passive home is so tightly
constructed that it needs no
heating or cooling source
HERS Index: Home Energy Rating System
• Set by Residential Energy Services
Network (RESNET)
• Scoring system scaled from 0 - 200
• Zero net energy home = 0
• “Reference” new home = 100
• Most older homes = well over 100
• Each 1 point decrease in HERS = 1%
reduction in energy consumed
HERS measures:
-Building Enclosure
-Mechanical Systems
-Renewable Energy
Massachusetts: acting to reduce energy use
ahead of federal changes
First major step towards Zero
Net Energy Buildings: amend
the State Building Code
Massachusetts adopted the
International Energy
Conservation Code (IECC) 2009
as its new state building code,
effective January 1, 2010
Increases energy efficiency
requirements by 10% over the
current base code
ZNEB establishes regulatory and
financial incentives for deepenergy retrofits
Directs utilities to pilot 250 deepenergy retrofits in existing homes
Stretch code: local option allows more stringent energy
standard that “stretches” the base code requirements
Residential alterations &
renovations can meet
stretch code by
– Prescriptive path
– Performance path
Prescriptive meets:
Energy Star for Homes
requirement (HERS 80)
Performance meets:
HERS of 80
(houses over 2000 sf)
HERS of 85
(houses less than 2000 sf)
HERS case study for stretch code:
Cambridge MA triple-decker, 2009
Existing = vinyl replacement
windows , R-10 ceiling insulation;
11 ACH @ 50 Pascals pressure;
no mechanical ventilation
Initial HERS rating = 143
Retrofitted with R-13 wall
insulation, R-30 ceiling insulation,
air sealed to 5 ACH @ 50
Pascals, bath fans added
Improvement cost = $14,847
Improved HERS = 85
With 3 new gas boilers @ 86%
Upgraded cost = $29,395
Upgraded HERS = 80
What is recommended generally
(in the rest of the US)
Oak Ridge National Laboratory:
“Insulation Recommendations for
Existing Wood-Framed Houses”
Most energy interventions assume your house
looks like this . . .
but what if your house looks like this?
Traditional active and passive interventions support
energy efficiency in an old house
Traditional practices
and design provide the
starting point for
energy savings
Passive and active
energy measures are:
- Economical
- Reversible
- Work with the historic
structure and materials
George Nash, Renovating Old Houses
Preservation concerns in insulating older and
historic houses . . .
1. We don’t know how these
materials and techniques
will respond over time (we
need more materials
science research)
2. It’s complex: contractors
are unlikely to know how to
properly install them (we
need standards for training
weatherization contractors
on old houses)
Boston Globe, January 18, 2009
“Arlington house may blaze new trail in
energy conservation”
3. It’s expensive to do it right
(so how many people will
be able to afford to retrofit
Super-insulation/deep energy retrofits of old houses require careful
planning and affect historic materials and finishes
Save energy costs and reduce consumption in an older
home without losing historic material and character
KISSS: Keep it simple, start small
•Air Seal
-Energy audits using a blower door
test show areas of air leakage
-Caulk inside and out to close
gaps and stop air movement
-Weatherstrip windows and doors
•Insulate Attics
-Seal areas of air infiltration
-Add loose fill or batt insulation
•Seal and Insulate Ducts
•Insulate Hot Water
Heaters and Pipes
. . . and REPAIR your wood windows!
Air Infiltration:
Blower door test diagnoses sources
Infrared camera monitors locations of heat loss
Comprehensively seal sources
of air infiltration by caulking gaps
Exterior: Use modified silicone polymer or backer
rod and expanding polyurethane foam
(foam must be painted to resist weather)
Interior: Use water-based latex
Insulate attics with fiberglass or other batting, or loose-fill
insulation; air seal gaps before installing insulation
George Nash,
Renovating Old Houses
Seal and insulate ducts; insulate hot water pipes
High efficiency appliances
But what about insulating walls?
The big question for old house owners
Wall insulation is often recommended for energy retrofits in
existing houses
Adding insulation to exterior wall cavities is difficult unless the
walls are open
When walls are insulated, comprehensive measures to air
seal, provide proper moisture barriers, and adequately
ventilate interior air must also be taken
Wall insulation: not right for all houses
Sprayed in place open or
closed cell foam insulation:
– Provides superior
– Comprehensive air
sealing and
– Good moisture control
BUT it also:
– Requires removal of
interior finishes and
plaster and whole house
– Obscures historic fabric
– Is not reversible
Blown-in cellulose: the jury is still out on this . . .
Rely on Department of Energy/Oak Ridge
National Laboratory web sites for
DOE and ORNL advise:
-adding insulation to an old house is
complex and difficult
-older wiring in walls retrofitted with
insulation can be a fire hazard
-potential moisture problems must be
mitigated through 1) excluding water entry,
2) ventilating interior moisture, 3) stopping
air leaks, and 4) providing proper attic
-More data would help a lot!
The preservationist’s nightmare
Proactive approaches to balancing preservation
and energy goals
Tailor interventions to age,
building type, or significance?
Older houses (1870-1950)
- Use “modern” dimensional
lumber, balloon/platform framing
- Originally included central
heating systems
- Often built with stock millwork,
trim, architectural elements
Should be able to accept wall
insulation without serious loss
of integrity
Avoid “energy improvement experiments” on the oldest
and most significant properties
“Historic” houses (1680-1850)
- Use pre-industrial timber or
Eastern braced framing
- Not constructed with central
heating systems
Very significant or rare houses
May not be suitable for wall
insulation energy retrofits at all
Insulation Interventions
for Older and Historic Houses
To summarize:
• Keep it simple, start small
Air Seal
Insulate Attics
Seal and Insulate Ducts
Insulate Hot Water Pipes
• Extensive energy retrofits are costly, complex,
and potentially destructive of historic character
and materials
• Be wary of wall insulation
• Consider information sources carefully
With care and common sense, every old house can be

Recommendations of the Governance Task Force