sheathing as part of an energy retrofit can be
it’s dense-packed (3 lb. to 4 lb./cu. ft.), that
effective, but it’s also complicated, not only in
increased density stops most air infiltration,
detailing around doors and windows but also in
although dense-pack is not an air barrier per se.
making sure you get the right amount of foam
In fact, some New England contractors report
for your climate zone.
that old houses retrofitted with dense-packed
Extruded polystyrene (xPS) is intermediate in
cellulose are as airtight as new houses with poly-
price and R-value (R-5 per in.). Panels thicker
ethylene vapor barriers. For the merits of cellu-
than 1 in. have a perm rating of less than 1, so
lose versus fiberglass, read the previous section,
XPS is the most water-resistant of the three
“Loose-Fill Insulation”.
foams and thus best suited for insulating founda-
RIGId-FoAM InSulATIon pAnElS
Rigid-foam panels are less permeable (p. 397)
than any insulation material except polyurethane
R-Values of Common
spray foam. Thus, when correctly installed, pan-
els can reduce air and moisture infiltration, elim-
Building Materials
inate heat loss due to thermal bridging (p. 192),
MATERIAl
R-VAlUE
and increase R-value. Retrofitting panels to a
building’s exterior—over wall or roof sheathing—
is invariably a major undertaking, however, so
8-in. concrete (solid)
0.90
try to coordinate it with other compelling renova-
4-in. common brick
0.80
tion tasks such as stripping a worn-out roof or,
say, replacing asbestos siding. Incorporating the
31⁄2-in. wood stud (on edge)
4.5
additional thickness of rigid-foam panels into
1⁄2-in. plywood sheathing
0.63
exterior assemblies also takes great skill, so make
sure a seasoned crew is assigned to it. On the
3⁄4-in. plaster or 1⁄2 -in. drywal
0.40
other end of the skill spectrum, panels can be
Glass
a quick and cost-effective way to create a dry,
finished basement.
Single pane
0.89
There are principally three types of rigid-
double pane
1.91
foam panels used in residences, and each has
characteristics that suggest where it can be best
Triple pane
2.80
used. All three types are available in 2-ft. by 8-ft.
or 4-ft. by 8-ft. panels with thicknesses from 1⁄2 in.
to 2 in., and all come unfaced or foil-faced.
Facings reduce breakage, make panels less per-
meable, protect foam cores from degradation,
and give panels greater cohesion. Rigid-foam
panels have relatively poor UV and fire-resistance,
so check with local code authorities before
installation.
Expanded polystyrene (EPS), the classic white
styrene board, is a closed-cell foam. EPS is the
least expensive of the three types, with an R-value
of R-4 per in. Unfaced, EPS is semipermeable
(5 perms per in.), allowing water vapor to
migrate through it, without degrading it. Of late,
building scientists favor allowing some moisture
migration, so EPS is a good choice for finishing
basement walls (see p. 417). Termites and beetles
sometimes nest in rigid foam, so if you are think-
ing of installing it over exterior sheathing, con-
sider a borate-treated variety of EPS, such as
Perform Guard®. EPS is also the most environ-
Rigid-foam insulation panels such as polyiso cut easily with a crosscut saw. To reduce
mentally benign type.
the movement of air around panel edges, seal them with a compatible canned spray
foam or caulk.
Energy Conservation and Air Quality
409
tions. This closed-cell foam also has the highest
density, it may be the better choice on houses
compressive strength of the three, so it can with-
framed with smaller lumber. For example, 2x4
stand the roughest usage; it is widely used as
walls sprayed with 2-lb. foam can attain an
exterior sheathing. XPS can be readily identified
R-value of 26 or higher. Less expansive than
by its pastel hues: pink, green, blue, and yellow.
open cell, closed-cell foam is typically installed
in several passes, which often results in greater
Polyisocyanurate (polyiso or PIR), the most
control and less trimming. To avoid excess heat
costly and most effective insulation, has an initial (and subsequent shrinkage), no more than
R-value of 7.4 per in. and a residual R-value of
11⁄2 in. of closed-cell foam must be applied in
R-6.5 per in. A closed-cell foam, it has the lowest
each pass (“lift”).
compressive strength of the three—though its foil
facing improves its durability. Foil-faced polyiso
A skilled installer is essential. Sprayed poly-
is commonly used on roofs because of its high-
urethane foam is a remarkable performer if
temperature stability.
applied precisely. But if its chemical components
are not heated to the correct temperature, mixed
SpRAy polyuRETHAnE
in the right ratio, and applied in the prescribed
FoAM InSulATIon
thickness, the foam may not cure correctly and
could emit noxious fumes for months. If the sub-
Spray polyurethane foam (SPF) is usually a two-
strate being sprayed is too moist or too cold, the
part foam whose components travel through sep-
installation can fail. So the best advice I can give
arate, heated hoses to mix at the spray gun noz-
is to find a reputable installer. A seasoned install-
zle. Sprayed wet onto a surface, the chemicals
er will also understand the importance of ventila-
undergo an exothermic reaction (give off heat),
tion during and after the installation and so will
foam and expand dramatically, then gradually
advise workers and homeowners about safe levels
harden as they cure. Because polyurethane foams of exposure.
expand 25 to 100 times the volume of the wet
In response to consumer concerns about lin-
mixture, SPF air-seals and insulates superbly. It
gering smells and potential health problems,
adheres well to a variety of surfaces and fills
information clearinghouses have emerged.
hard-to-reach spaces such as the roof–sidewalk
Canadians can find spray-foam insulation con-
juncture better than any other sealant. Correctly
tractors whose products meet the National
mixed, applied, and cured, SPF is inert, nonoff-
Standard CAN/ULC/S705.1 by visiting www.
ga
ssing, and odorless and thus is safe in both
sprayfoam.com. In the United States, the Air
interior and exterior applications.
Barrier Association of America (ABAA) lists
How much the foam expands determines its
accredited contractors and describes its on-site
density, its R-value, its permeability to water
quality-assurance program at www.airbarrier.org.
vapor, how much material must be used and thus The ABAA also can recommend a third-party
its cost, how the foam must be applied, and
auditor who will check on the job.
where it may be used. Foam that is more expan-
But proving cause-and-effect is difficult, even
sive and less dense is called open cell; foam that
with an army of auditors testing the air in a
expands less and is denser is closed cell.
house. Many building materials are used in a
open-cell foam weighs about 0.5 lb./cu. ft. and
renovation, any one of which could contain
has an R-value of 3.6 per in., roughly the same as chemicals or glues that could offgas for a time.
fiberglass batts or loose-fill cellulose. Although
Hard data are hard to come by when pursuing
open-cell foam is an effective air sealant, it is
airborne pollutants, smells, and side effects.
semipermeable to water vapor; thus it must not
be used on exterior applications. In interior uses,
oTHER SpRAy FoAMS
local building codes may require that it be used
Polyurethanes are the dominant spray foams
with a class II vapor retarder (p. 397). Because of today, but new formulations should emerge in
its lower R-value, open-cell foam must be applied the coming decades. One such alternative, Air
thicker, so framing members must be deeper to
Krete®, has been on the market for about
accommodate it. Given its great expansion
10 years. It is applied through a fine screen
(100), open-cell foam is installed in one pass
stretched across open studs and attains an
and the excess is trimmed away.
R-value of 3.8 per in. It is formaldehyde-free,
closed-cell foam weighs about 2 lb./cu. ft. and
mold-resistant, pest-resistant, and has good
has an R-value of 6.5 per in. With a perm rating
sound-deadening qualities. Once the foam cures,
of less than 1, 2 in. of closed-cell foam is a class II it can be cut with a handsaw. Because its princi-
vapor retarder and thus well suited to exterior
pal ingredient is magnesium oxide, an inert min-
applications. Given closed-cell foam’s greater
eral, Air Krete has good fire-resistance as well.
410 Chapter 14
Instal ing Insulation
As part of an overall renovation plan, try to time
installing insulation so that it coincides with
other major tasks. For starters, it will save
money. When the roof is worn out and needs
stripping, for example, it is relatively easy to
cover roof decking with rigid foam before
reroofing. If siding with asbestos must be
removed, exposing the sheathing will facilitate
retrofitting exterior foam panels or blowing
dense-pack cellulose into wall cavities.
Installing insulation could fill many books, so
below you’ll find representative installations for
each of the five major types of insulation.
InSTAllInG FIBERGlASS BATTS
All batts are installed in basically the same way,
so these tips for installing fiberglass batts also
Air Krete, is one example of many nonpolyurethane spray foam insulations.
hold true for cotton and mineral-wool batts,
unless otherwise noted.
Getting started. Carefully seal air leaks before
insulating; air currents can dramatically reduce
hoW Much InSUlAtIon do yoU nEEd?
an installation’s R-value. Then suit up with the
How much insulation you need depends on climate, the house’s heating system, and
appropriate safety gear to keep fiberglass off your
skin and out of your lungs. Wear a respirator, eye
which part of the house you’re insulating, as shown in “Recommended levels of
protection, long-sleeved shirt, long pants, and
Insulation” on p. 407. Or you can use the U.S. Department of Energy’s interactive
work gloves.
Zip Code Insulation Program, which is free online at: www.ornl.gov/~roofs/Zip/
To determine how much insulation to buy,
ZipHome.html
measure the square footage of walls, ceilings, and
To get a detailed insulation plan, type in your zip code, then check the boxes that
floors and then divide by the number of square
best describe the house. Major insulation manufacturers offer similar calculators. You
feet in an insulation package. Also printed on the
should also consult your local building authority, which has the final say and, in many
packaging is the insulation’s R-value and the
cases, can tell you about tax incentives or rebates that encourage homeowners to
width of the batts. Because most joists, studs,
insulate and save energy.
and rafters are spaced 16 in. on center, 15-in.-
wide batts are the most common size. The fewer
cuts you make, the faster the job will go; thus
many contractors buy precut 93-in. batts to insu-
late standard 8-ft. walls. (Although 8 ft. equals
If stud walls are exposed, always seal
96 in., the 3-in. shortfall in batt length anticipates
air leaks before you start insulating.
the space occupied by the top and bottom plates.)
Batts that long can be a bit unwieldy, though, so
you might want to use precut 4-ft. batts in those
stud bays where you must fit insulation around
pipes and wiring.
When no vapor retarder (p. 397) is required
or one will be installed later, many contractors
prefer to install unfaced batts. They’re quicker
to install because there’s no facing to cut
through, and you can friction-fit the batts. By
contrast, kraft paper–faced or foil-faced batts
must be cut carefully to avoid tears and stapled
to framing. In general, place insulation facing
toward the side of the building that’s usually
warmer—in cold climates, place the facing
toward the inside of the building.
Energy Conservation and Air Quality
411
cutting and placing insulation. Fiberglass
not the sides—of studs or rafters. Use a hammer
P R O T I P
insulation cuts easily with a utility knife,
tacker with 3⁄8-in. staples.
although you’ll have to make several passes.
Before insulating attic floors,
Insulating the attic. First, seal air leaks and add
Change the blade as soon as it gets dull.
locate electrical boxes and
baffles (pp. 398 and 400) to keep batts from
Professional insulators use a long-bladed insula-
IC-rated recessed lights. using
blocking soffit vents. If attic floor joists are
tion knife or hone one edge of a putty knife until
coat hangers and
bright scrap
exposed, place planks across them so you can
plastic, make little flags about
it’s razor sharp. A common way to cut an insula-
move safely. (Stepping from joist to joist is a good
1 ft. high and staple them to the
tion batt is to place it on the subfloor, measure
way to step through the ceiling.) If there is a
joists near each box or fixture.
off a cutline, and press a 2x4 into the batt to com- rough floor and you’re not going to finish the
when the floor is covered with
press the insulation and guide the knife. If you’re attic, you might consider removing floorboards
insulation, those little flags will
cutting several pieces to the same length, you can every 6 ft. to 8 ft. and blowing in loose-fill insula-
show you where the electrical
save measuring time by marking the batt length
tion. But batts are easy enough to install if you
elements are, should you need to
on the subfloor with masking tape. To cut faced
can pry up floorboards and insulate the floor in
access them.
batts cleanly, place the facing side down on
sections. Starting at one side of the attic, pry up
the subfloor.
and stack the floorboards, place batts, and renail
Many insulation contractors prefer to insert
floorboards before moving to the next section.
batts into stud bays and trim them in place. To
Fitting batts is pretty straightforward. Cut
trim a batt for a narrow bay, place one side of the batts to length and place them so they fill the
batt into the bay and use the stud on the other
joist bays completely. If there’s diagonal bridging,
side as a cutting guide. To get a tight fit, cut the
slit batts down the middle, 4 in. to 6 in. from the
batt about 1⁄4 in. wider than the stud bay. As you
end, and fit the slit ends around the bridging. As
place batts, make sure they fill the bays fully.
in walls, split batts (see the photos on the facing
Fiberglass insulates best at “full loft,” so before
page) to feed them over and under wires and
placing a batt between studs or joists, shake it
pipes. Note: Keep insulation and other combusti-
gently to plump it up to its full thickness. If you
ble materials back at least 3 in. from masonry or
need several batts to fill a bay, butt their ends
metal chimneys and non-IC-rated recessed light
together rather than overlapping and compress-
fixtures, as described on pp. 392–393. When add-
Renovation 4th Edition Page 96