| |
Airtight Drywall
Approach and SimpleCS
Since the early 1970s, sealing the
building envelope has been recognized as an important component in energy
efficiency and structural durability. In a poorly sealed home, heated air
flows out through cracks and seams in the building envelope—ceilings, walls,
windows, doors, and other penetrations around the building exterior. Moisture,
carried into the wall and ceiling cavities by air movement or by vapor
diffusion, may damage building insulation and structural materials.
Sealing the building envelope requires
both a vapor diffusion retarder and an air retarder. A vapor diffusion
retarder must restrict vapor diffusion, which is the movement of water vapor
through a material. The amount of water vapor moved by diffusion in a wall
cavity is minute compared to the vapor moved through the same wall by air
movement. An air retarder inhibits the movement of air in and through cracks
and seams in the wall. To do this effectively, it must meet certain criteria.
The material must be continuous and virtually impermeable to air. It also must
be able to withstand the air pressure loads that act on it.
There are three main methods of
air-sealing the envelope: polyethylene wrap, Airtight Drywall Approach (ADA),
and SimpleCS (SCS) (pronounced "simplex" and standing for
"Simple Caulk and Seal").
Until recently, the most widely used
method of sealing the building envelope was to carefully install and seal
polyethylene sheeting. The sheeting acts as an air retarder and a vapor
diffusion retarder. Since air retarders and vapor diffusion retarders serve
different functions and have distinct characteristics, it may be more
practical to install them as separate systems.
Although polyethylene sheeting meets the
requirements of both air retarders and vapor diffusion retarders, it has some
serious drawbacks as an air retarder. The installation process necessary to
maintain a proper seal is complicated. During and after installation it may be
subject to cuts and tears that make it ineffective as an air retarder.
While polyethylene is an effective vapor
diffusion retarder, other building materials that are already being installed
can be made to work as a more effective air retarder. The Airtight Drywall
Approach (ADA) uses the drywall already being installed, plus gaskets and
caulking, to create a continuous air retarder.
ADA was created in Canada in the early
1980s by Joe Lstiburek, a building scientist. Although it is quite effective
as an energy-saving technique, it was designed to keep airborne moisture from
damaging the insulation and building materials within the wall cavity.
SimpleCS, a variation on ADA, also uses
drywall and sealant. It differs in its use of some air-sealing techniques and
when they are applied in the building process. The guiding principle for both
systems is to make an effective air retarder by sealing the drywall to the
building structure. Both systems require a separate vapor diffusion retarder,
such as polyethylene sheeting, Kraft paper-faced insulation, foil-backed
wallboard, or vapor-impermeable paint.
Both ADA and SimpleCS systems use
various sealing materials, depending on location and application. Long-life,
highly elastic sealants and/or compressible, open-cell gaskets (often
saturated with resins) maintain a complete seal during the normal contraction
or expansion of the building materials. Spray foam insulation seals large and
irregular gaps, except for locations that present a fire hazard.
The Airtight Drywall Approach seals the
points where the foundation, sill plate, floor joist header, and subfloor meet
each other. The space between floors, the subfloor, rim joist, and plates is
also sealed. The wall framing plates are sealed to the lower subfloor and the
upper rim joist.
Finally, ADA applies gaskets at the top
and bottom wall plates between the drywall and the framing members, and
between drywall and perimeter attic joists. Taping and floating the drywall
seams creates a continuous air retarder. Where interior partition framing
meets the exterior, ADA adds gaskets to the drywall on exterior walls and
ceilings to the end stud and top plate of the interior partition.
The majority of this sealing work occurs
just before drywall installation. There are, however, two exceptions. The top
rim joist and wall plates are gasketed to the subfloor by the framing
carpenter. Special electrical boxes with flanges provide continuous air-
sealing to the vapor diffusion retarder or drywall, simplifying this difficult
connection. In each case, you should use a compatible sealant during or soon
after drywall installation. Windows, doors, and other exterior penetrations,
such as pipes and cables, are sealed with sealant or plastic sheeting, either
during material installation or right before installing insulation.
The SimpleCS air retarder approach is
very similar to ADA, but the sequence and location of sealing are often
different. In SimpleCS, rather than gasketing between framing joints to seal
the rim joist between floors, pre-cut blocks of rigid foam insulation seal the
floor joists, sheet subfloor, and top plates.
The most significant variation in these
systems is in the sealing of the drywall. Unlike ADA, SimpleCS seals the
drywall AFTER the drywall installation and taping. Closing joints between the
drywall and the subfloor, ceiling, and all interior partitions with sealant
and spray foam creates a continuous air retarder.
Contractors who use the SimpleCS
approach claim that the sequence is less disruptive to framers, drywallers,
and electricians. These subcontractors claim that ADA makes their job more
complicated. For example, some framers claimed that gasketing altered the
spacing on rim joists and wall plates, making it more complicated to hang
floor joists. Postponing sealing until after drywalling also results in a
cleaner, dryer environment in which to perform the task.
There have been limited short-term tests
done on SimpleCS-constructed homes. So far the results seem very similar to
ADA homes. In one long-term test, the ADA test homes had, after one year, 0.67
to 1.80 air changes per hour (ACH) at 50 Pascals pressure. Identical
conventional homes with no air retarder had 2.23 to 2.59 ACH at 50 Pascals.
ADA test houses using 2+6 walls (38+140
mm) and R-20 insulation require 23% to 32% less heat than conventionally built
homes with the same specifications. Also, test measurements of airborne
contaminants in homes implementing ADA techniques (including mechanical
ventilation) indicated that the reduction of air infiltration did not diminish
the indoor air quality.
Bibliography
The following articles provide additional
information about Airtight Drywall Approach or SimpleCS. This bibliography was
reviewed in July 1996.
Books
Air-Leakage Control Manual, J.
Maloney, Bonneville Power Administration, 1991. Available from Bonneville Power
Administration (BPA), P.O. Box 3621, Portland, OR 97208-3621, (800) 662-4519 or
(503) 230-7334. $7.00 (softcover).
The Airtight House, J. Lischkoff
with J. Lstiburek, Iowa State University Research Corporation, 1986. Available
from Iowa State University, Extension Distribution Center, 119 Kooser Drive,
Iowa State University, Ames, IA 50011, (515) 294-5247. 84 pp., $12.95 (softcover),
Publication no. EES101.
A Builder's Guide to Energy Efficient
Homes in Georgia, J. Tiller and D. Creech, Governor's Office of Energy
Resources, 1990. Available from the Georgia State Energy Office, 2080 Equitable
Building, 100 Peachtree Street, NW, Atlanta, GA 30303-1901, (404) 656-5176. 125
pp., Free (softcover).
NY-STAR Builder's Field Guide,
NY-STAR, Inc., 1994. Available from NY-STAR, Inc., 41 State Street, Suite 1011,
Albany, NY 12207, (518) 465-3115. 247 pp., $12.00 (softcover) plus $3.00
shipping and handling.
Residential Building Design &
Construction Workbook (2nd Ed.), N. Nissan, Cutter Information Corp., 1988.
Available from Cutter Information Corp., 37 Broadway, Arlington, MA 02174, (800)
964-5118. 347 pp., $95.00 (softcover).
Super Good Cents Builder's Field Guide
to Energy Efficient Construction, T. Haskell and B. Boe, Bonneville Power
Administration (BPA), 1992. Available from Bonneville Power Administration (BPA),
P.O. Box 3621, Portland, OR 97208-3621, (800) 662- 4519 or (503) 230-7334.
$10.00 (softcover).
Articles
"ADA: New Approaches," R.
Kadulski, Solplan Review, (No. 16) pp. 12-13, August/September 1987.
"ADA Performance," R. Kadulski, Solplan
Review, (No. 18) pp. 7-8, December/January 1988.
"Air and Vapor Barriers," S.
Gibson, Fine Homebuilding, (No. 88) pp. 48-53, April/May 1994.
"Air Barrier Details: How Effective
Are They?" R. Kadulski, Solplan Review, (No. 46) pp. 3-5,
August/September 1992.
"Airtight Drywall Approach," J.
Lstiburek, Solplan Review, (No. 2) pp. 5-7, April/May 1985.
"The Airtight Drywall Approach: 1988
Approach," L. Fox, Northeast Sun, (6:2) p. 16, April 1988.
"Airtightness the Simple(CS)
Way," S. Andrews, Home Energy, (6:6) pp. 28-32, November/December
1989.
"Building Scientists Turning
Construction Code and Common Practices Upside Down," J. Nisson, Energy
Design Update, (14:6) p. 3, June 1994.
"Controlling Air Leakage," J.
Maloney, Fine Homebuilding, (No. 77) pp. 64-67, October/November 1992.
"Draft-Free Construction," R.
Kadulski, Solplan Review, (No. 27) pp. 7-10, June/July 1989.
"Form Gasket Tests for Airtight
Drywall Approach," J. Nisson, Energy Design Update, (6:12) pp. 4-5,
December 1987.
"The Last Word (We Hope) on Vapor
Barriers," JLC Staff, Journal of Light Construction, (11:11) pp.
13-15, 17, August 1993.
"Ordinary Paint as Replacement for
Poly Vapor Retarder," J. Nisson, Energy Design Update, (14:5) pp.
6-7, May 1994.
"The Oregon Field Test," J.
Maloney, Fine Homebuilding, (No. 37) pp. 62-65, February/March 1987.
"Plastic Vapor Barriers with
ADA," J. Nisson, Energy Design Update, (5:6) pp. 6-8, June 1986.
"Stop Energy Loss and Moisture
Build-Up—Cold!" J. Obst and L. Hendricks, Home Energy, (8:4), pp.
14-20, July/August 1991.
"Tight Construction Made
Easier," J. Maloney, New England Builder, (5:11) pp. 38-39, August
1987.
"With Joe Lstiburek," C. Wing, Northeast
Sun, (6:2) pp. 14-15, April 1988.
Energy Efficiency and Renewable Energy
Clearinghouse (EREC)
P.O. Box 3048 Merrifield, VA 22116
Voice: 1-800-DOE-EREC
E-mail: doe.erec@nciinc.com
Path:
Home>Education>Healthy
Home Information>Airtight
Drywall Approach and Simple CS
|
|
