BUILDING ENVELOPE: Infiltration
Questions:
Where are the most critical air leaks
in a home?
These are likely to be found in the attic, as holes around plumbing and electrical
lines, and other gaps in framing. If this is an existing home, move the insulation
out of the way to find many of these. Using a foam sealant, regular caulk
and small pieces of foam board, seal all the penetrations possible. Look for
other openings in both exterior and interior walls, including plumbing openings
behind bath and kitchen cabinets.
Residents should be sure to replace the insulation and avoid leaving gaps
between fiberglass batts. In homes with a basement, owners should look for,
and seal, the same kind of holes in the ceiling and floor framing that open
into the interior cavities of the house.
After sealing is done, consider adding insulation to the attic. An attic should
be insulated to an R-38, or about 12 inches fiberglass or cellulose. When
adding attic insulation, cellulose can be blown directly on top of either
fiberglass or cellulose. Many lumberyards will loan the equipment when purchasing
the insulation from them.
For additional help, a do-it-yourself energy audit is available online at
the Energy Extension Web site at http://www.oznet.ksu.edu/dp_nrgy/ees/.
Some may also choose to hire a certified Kansas home energy rater. Call Energy
Extension at 1-800-KSU-8898 for a list of professionals.
What is an air barrier, or house wrap?
These products are primarily designed for use in new construction as a method
of reducing air infiltration. They are rolled sheet goods usually installed
with staples or tape over the exterior sheathing.
Some brand names are Tyvek, Rufco-wrap, Barricade and Airtight-wrap. Their
intent is to minimize the passage of air, while still allowing water vapor
through the exterior skin of the building.
Three basic types currently are available. Tyvek is a spun-bonded polyethylene.
This is a mat of polyethylene fibers spun-bonded in a patented process. The
second type is perforated polyethylene film. The third type is spun-bonded
polypropylene, a different type of plastic.
Each of these can be effective air barriers if installed according to its
manufacturer's recommendations.
How effective is covering windows with
plastic at sealing a window?
Properly applied, a plastic covering can make a window almost airtight. This
is one of the most effective ways to seal a leaky window.
A storm window is designed more for convenience and appearance than air tightness.
Even the highest quality storm windows allow air to leak around the edges
of the sashes. Storm windows typically reduce air leakage through primary
windows by about half.
Window plastic can be installed on the inside window surface or on the outside.
It will be more difficult to maintain window plastic applied to the outside.
Cold temperatures make the plastic brittle, and winds whip the plastic in
and out, reducing the seal's effectiveness and sometimes even tearing the
plastic.
Newer plastics are very clear when stretched tight, so do not need to worry
about window coverings reducing a home's appearance. Special shrink film plastic
can be heated with a blow dryer to shrink the window film and eliminate all
wrinkles, making the plastic almost invisible.
For maximum leak reduction, it is important to adhere the plastic to the frame
surrounding the window rather than to the window sash.
