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Blown-In Wall
Insulation
Written by
Joe Lamy
It is always advisable to insulate walls.
You'll benefit from increased comfort and savings. Before installing wall
insulation you may want to investigate materials and techniques. In an existing
home, it's generally wise to limit your investigation to blown-in insulation,
unless planned renovations will expose wall framing. For this reason, this
factsheet provides information on materials and methods used in blown in
insulation. It also includes tips to help you select a professional contractor
to do the job.
Why Insulate?
Uninsulated walls lose heat more quickly
to the outdoors. This heat loss can cause
- Drafts across the floor,
- Discomfort from loss of body heat to
cold wall surfaces,
- higher heating costs,
- Condensation on the interior surfaces
and ideal conditions for mold growth, mildew and decay, and
- condensation within the wall cavity.
Insulating the wall increases its
thermal effectiveness. The insulation:
- Reduces drafts caused by air leakage
through the wall cavity;
- Keeps the interior surface warmer so
occupants can lower the thermostat, but still be comfortable;
- Reduces movement of sound waves and
dust so the house is quieter and cleaner; and
- Reduces potential for condensation
and related problems.
Investing in wall insulation pays for
itself with savings on the heating bill. Average payback is less than 5 to 10
years. Your actual period of payback will depend on factors such as lifestyle,
home construction, and the cost of heating fuel.
Materials
There are several materials used to
insulate the wall, with varying costs and effectiveness. Materials include
cellulose, mineral fibers, and foam insulation. Some contractors also offer
vapor barriers and vents as part of the installation.
Cellulose is made from
shredded newsprint, treated with fire retardants. Monitoring by industry and
government assures the homeowner the material has a standard R-value, is
non-toxic, and will not burn or cause corrosion of pipes or wires. Cellulose
is particularly effective in wall installations because of its ability to fill
and pack even in tiny nooks and crannies within the cavity. Cellulose is also
very effective in reducing air infiltration through wall cavities.
Mineral fibers such as
fiberglass and rock wool are installed in some walls. Greater pressure is
required to pack these materials into the cavity because they tend to catch on
nails and hang up around tight places. In addition, larger drill holes are
needed to install this type of material. Mineral fibers are most appropriate
in homes or walls where moisture is a serious problem, because mineral fibers
do eventually dry out. (Cellulose generally does not dry out once wet.)
Foam insulation has
been used in the past, but is not as widely used today. Although it offers
higher R-values than either cellulose or mineral fibers, problems have been
experienced with blown in foam. This includes expansion of the foam during
installation causing bowing of walls, and shrinkage of the foam over time,
causing gaps in the insulation.
Installation could also include vapor
barriers and vents. Almost all the moisture that creeps into the wall cavity
arrives through holes and small cracks on the interior wall. Very little vapor
passes through holes and small cracks on the interior wall. So a vapor barrier
such as rated paints or visqueen is not necessary. Similarly, a vent plug on
the exterior is not recommended.
Installation
Techniques: What to Expect
Gaps or voids in any insulation
material, account for significantly poorer thermal performance, so proper
installation is important.
Wall insulation is more complicated to
install than attic or underfloor insulation. It's best to contact a
professional insulation contractor. A professional has the experience to work
efficiently, effectively, and recognize unexpected problems.
An experienced crew with good equipment
can insulate the walls of an average house from start to finish in less than
one day. One crew member drills the wall cavities and probes for blocking.
Another follows with the nozzle and hose from the blowing machine and fills
the cavity with insulation. An ordinary wall section that is 8 feet in height
requires two holes, one about 12 inches below the trop of the wall and the
other one up about 36 inches from the bottom of the wall. A wall 10 feet in
height may need three holes to achieve adequate compaction of the insulation
throughout the cavity (depending on the equipment).
After the installation, the holes are
plugged with a wood or plastic plug. The plug is painted if the homeowner
supplies the paint. Another option includes a plug with spackle over it. Most
insulation contractors stress this is not a finished job and matching colors
and textures is not their specialty. Plugs installed without adhesive may work
their way out over time because of changing moisture content and temperature.
Patching compounds can be textured to blend with existing surfaces.
After the work is completed, a
professional installer is required by law to leave a certificate that
specifies how much material was installed, how many square feet it covered,
type of material used, date of installation, and the installer's name. To
prevent settling of material (that could result in voids or gaps), contractors
install more insulation in each cavity than will it holds at settled density.
For example, cellulose will settle to a density of 2.3 pounds per cubic foot,
but your contractor should press more than 3.0 pounds into every cubic foot.
The possibility of settling is then greatly reduced.
Shopping for a
Contractor
Finding a professional to install your
wall insulation begins with gathering names of two or three reputable
contractors who are willing to inspect your house and make an estimate or bid
on the job. Friends, neighbors, or your utility company may be the best source
for referrals. In addition, the Yellow Pages directory lists most local
contractors. Check under the heading, "Insulation Contractor - Cold and
Heat." Often the directory will tell you what areas the contractor
serves, what insulating materials are used, and whether the contractor is a
member of any professional associations.
The inspection will give you a chance to
determine whether you're comfortable in dealing with the contractor. It's best
to get three bids. Don't be afraid to ask for recent references and to contact
them. A few minutes on the phone may provide the security of knowing you are
dealing with a responsible professional.
There are several aspects of
contractors' bids to compare. They include:
Intangible qualities.
Personality and reputation leave a strong first impression. Select a
contractor who respects your wishes and property and has strong references.
Price. A recent survey
of insulation contractors in Washington produced an average price of 50 cents
per square foot of wall area with easy access. The price includes drilling,
filling, plugging, and one coat of spackle over plugs. It does not include
painting.
Mineral fiber blown-in jobs generally
cost more because the material costs more. Also, as the job difficulty
increases, expect to pay a higher rate. For example, brick and stucco
exteriors can be difficult to penetrate.
Drilling access holes through interior
walls reduces the expense of access difficulties caused by masonry or asbestos
shingles, high ladder, or scaffold work. Raters for interior installation vary
depending on the amount of times it takes to cover and clean up the interior
and whether drywall or plaster and lath covers the wall. Average prices range
from 654- 85 cents per square foot.
Most kinds of exterior horizontal siding
can be removed and replaced carefully after the insulation is blown-in. The
procedure will preserve the integrity and original appearance of the siding.
Rates for this procedure vary widely, from 50 centers to $1.25 per square
foot, depending on whether this is a standard procedure for the company or
not. (Some companies report they actually prefer removing the siding rather
than having to deal with plugging and spackling drilled holes through the
siding.)
When comparing prices, note the area the
contractor estimates the job will cover. Two contractors may have the same
unit rate, but if they base their estimate on different areas, the total costs
of the two can be considerably different.
Clean up. Ask the
contractor how they handle clean up. If the project takes two days, do they
clean up each day? Do they seal pulley holes around widows? Do they install
gaskets around switch plates and outlets to prevent insulation from blowing in
the house? Do they take precautions when insulating around the bath tub,
stairwells, pocket doors, or built-in cabinets? If not done right, insulation
can be blown into the interior of the house, not the walls, creating a mess.
Warranty. Most
contractors install products that carry a warranty for one year. Many will
also warranty the labor for one year. Get both warranties in writing.
Other Services. If your
house needs other weatherization measures (attic and floor insulation or air
leakage controls), can the contractors give you separate bids for each? And an
estimated time of completion?
Washington State University Cooperative
Extension
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