Press Release - For Immediate Release
Date: Feb. 18, 2004
Contact: George Couch
Phone: (608) 231-9295
E-mail: gcouch@fs.fed.us
Many Home Repairs Fail to Solve Moisture Problems;
Researcher Presents 'Five Myths'
MADISON,
WI -- Each year American homeowners spend millions of dollars
attempting to fix or prevent moisture-related problems. Too often, their
efforts don’t
fix the problem. In some cases, these efforts actually make matters worse.
So says Anton TenWolde [CORRECT], a physicist and researcher who has been
studying moisture in buildings for more than 20 years.
According to TenWolde, many generally accepted moisture-control practices in
the United States are based on limited or no research but mostly on tradition
among home builders and others.
“We spend very little on housing research
in the United States. Several countries, including Canada and even smaller
nations like Denmark, the Netherlands and Sweden, invest more than the United
States in research into home-building technology,” he says.
TenWolde, a native of the Netherlands, holds degrees in physics and engineering
from the University of Delft in the Netherlands and the University of Wisconsin
at Madison.
He has been a physicist at the US Forest Service
Forest Products Laboratory (FPL) in Madison, Wis., since 1980. He is currently
project leader of the Building Moisture and Durability research unit there.
Since 1999, the FPL has been home to the Advanced Housing Research Center,
through which much housing-related research is managed and coordinated.
Several ongoing projects at FPL study moisture-related
issues. For example, FPL’s research-demonstration house, a full-size
four-bedroom house built in 2000, is equipped with scores of sensors embedded
in the walls and elsewhere to track the movement of moisture and water vapor
in the walls and foundation. Other projects look at sealants and wood-preservatives
as well as adhesives.
The problem of basing home construction or repairs on unproven building practices
is amplified because some of those traditional practices have become part of
building codes around the country, TenWolde says.
According to TenWolde, building codes historically
deal with safety issues such as fire prevention, electrical safety, or structural
standards. Building codes sometimes go beyond safety when they try to deal
with moisture.
“And moisture is one area where current building
codes get it wrong, especially when they apply standards that might make
some sense in northern Maine or Minnesota to Florida or Texas,” TenWolde
says.
TenWolde identifies five main ideas about home
construction and maintenance that are widely misunderstood or downright
incorrect. He calls them “The Five Myths of Moisture.”
Myth One concerns so-called vapor barriers, or
vapor retarders.
“ A vapor retarder, normally installed only
on exterior walls, is intended to slow the diffusion of moisture from an
area of higher humidity to one of lower humidity. Such barriers are ineffective
if there is any air movement, which is almost always the case in wood-frame
construction. An air barrier, to be effective, needs to envelop the entire
house—ceiling and floor as well as walls,” TenWolde says. “Problems
caused by diffusion are very rare; moisture problems caused by moving air
are much more common.”
In warm, humid climates, a vapor barrier can do
harm. Nonetheless, practically all building codes require vapor barriers
or retarders. (Vapor barriers originated in the 1930s, partly based on research
conducted at FPL.) A more effective approach to controlling moisture intrusion
would be to make the house as air-tight as possible and provide good drainage
around the house, according to TenWolde.
Myth Two is that attics need to have lots of ventilation. Again, venting requirements
are not based on rigorous scientific research.
TenWolde explains that attic venting originally
arose as a moisture-control strategy for cold climates. Other purported
benefits, such as longevity of the shingles, arose later. It is widely believed
that increased attic venting will prolong the life of roofing shingles by
cooling them. But research shows that venting has very little, if any, effect
on shingle temperature. The most important issue in shingle temperature
appears to be the color of the shingles. Light-colored shingles reflect
sunlight and don’t get as hot as dark shingles.
One possible real benefit of attic venting in
climates with large snowfalls is to reduce snow melt on the roof to avoid
the formation of ice dams. But according to TenWolde, a more effective—and
energy-efficient—way to control snow melt in almost all climates in
the United States would be to use air barriers and insulation to prevent
heat from entering the attic.
Myth Three is that new homes are built “too
tightly” and that walls have to “breathe.” That is the
reason often given for the presence of mold in newly built houses. TenWolde
cites recent research in Canada that revealed that houses that leaked air
had as much, or in some cases more, mold than tight houses.
“It takes very little air movement to accomplish
drying, and even a house with good air barriers usually will permit enough
movement to permit moisture to escape, unless there is massive water entry.
Uncontrolled air movement may actually cause moisture problems, and certainly
can cost money in air conditioning and heating,” he says.
Myth Four: Crawl spaces need to be vented. To
TenWolde, venting crawl spaces is just as dubious a practice as venting
attics. Venting crawl spaces is marginally effective in dry climates but
can be harmful in wet or warm humid climates. The best way to control moisture
in crawl spaces is to use site grading, downspouts and soil covers to prevent
water from entering the crawl space.
TenWolde’s Myth Five is the belief that
building codes actually address residential moisture problems.
“Building codes address only vapor “barriers” and
venting attic and crawl spaces. These are only two ways of controlling moisture
and not very effective ones at that,” TenWolde says. “Most real
moisture damage in homes is caused by water entering the home through leaks
or poor flashing details. The most effective practices for controlling moisture
are related to proper installation of windows, flashing, site grading, foundations,
rain absorption, roof overhangs, and whole-house ventilation and humidity
control.”
TenWolde’s “Five Myths” reflect
the fact that there is considerable confusion and misunderstanding around
moisture problems. In an attempt to resolve some of those differences and
publicize the latest research finings, the FPL has joined with industry-related
organizations to establish a Residential Moisture-Management Network. The
network will evaluate existing research and develop uniform recommendations
for dealing with moisture.
The US Forest Service Forest Products Laboratory
was established in 1910 with the mission of conserving and extending the
country’s wood resources. Today, FPL’s research scientists explore
ways to promote healthy forests and clean water, and improve papermaking
and recycling processes. Through FPL’s Advanced Housing Research Center,
researchers also work to improve homebuilding technologies and materials.
Additional information about FPL and its research activities is available
at http://www.fpl.fs.fed.us/.
###
APA - The Engineered Wood Association (formerly American
Plywood Association) is a nonprofit trade association whose domestic and
international members produce a variety of engineered wood products. APA's
primary functions are quality inspection and testing, applied research and
product promotion. |