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| Thermal Mass Benefits
of Log Homes Recognized |
The situation
could be cause for adopting an "I told you
so" attitude, but that won't happen. "The Log Homes
Council (LHC) doesn't feel smug, it just feels vindicated," says
Barbara Martin, LHC's executive director.
The situation in question is the fact the nation's Model Energy
Code finally recognizes the energy-conservation benefits of
thermal mass. This is a victory for the LHC. After 13 years,
its claim a log wall's thermal mass makes it as energy efficient
as a well-insulated frame wall has been acknowledged. Achieving
this acceptance has been a major goal for the LHC, a part of
the Building Systems Councils of the National Association of
Home Builders (NAHB).
While the claim is true, it wasn't officially acknowledged,
in part because thermal mass is difficult to quantify. Log
home owners had the home heating bills to prove it was true,
but Department of Energy and code officials needed more than
empirical evid ence. So, over the past 13 years, the LHC has
gathered scientific statistics from independent research projects
to substantiate its assertion.
Now that it has succeeded, Dave Carter,
LHC energy committee chairman, says "This makes life
easier for log home producers. We no longer have to fight
energy codes based on R-values.
It also helps log home owners. They don't have to invest in
additional b uilding materials to meet codes that do not improve
the livability of their homes."
R-value measures a material's resistance
to the transfer of heat from one side to another. Logs have
a relatively low resistance
to heat transfer. In fact, they actually absorb and store heat
in their cellular structure. This put logs at a serious disadva
ntage in the cold winter states. It forced producers to overbuild
their homes, especially thier floor, window and roof systems,
to meet total R-value requirements. "This drove up construction
costs without any measurable benefit to our buyers," says
Carter.
R-values have been at the heart of the debate all along. When
the energy crisis struck in the 1970's, the state and federal
governments quickly developed new energy standards for residential
construction. To assure compliance, officials needed a way
to me asure the energy performance of all residential building
materials. Since the situation was a crisis, and the R-value
methodology existed, it became the standard.
Thermal mass is a material's capacity to absorb, store and
slowly release heat over time. Logs do this well. The LHC set
out to prove two things. First, logs have thermal mass because
of their cellular structure, bulk and thickness. Second, this
thermal m ass provides significant energy-saving benefits because
it releases heat back into the house when temperatures drop.
Early studies proved thermal mass properties significantly
reduce heating and cooling loads in moderate climates. The
National Institute of Standards conducted the most important
of these studies for HUD in 1981-82. However, energy experts
continued to qu estion the value of thermal mass during the
winter months in northern climates. They doubted its benefit
when heat is needed constantly and thermostat settings are
opposite outdoor temperature.
Two recent studies, both conducted in cold climate states,
answer this question to the log home industry's benefit. In
1990, an independent testing agency, Advanced Certified Thermography,
conducted a study for the Energy Division of the Minnesota
Departm ent of Public Service. It focused on heat loss through
air leakage, assumed to be a problem with log walls because
of their many joints. The study found the industry has substantially
reduced air infiltration rates in the past 15 years. It credited
this r eduction to improve joint construction and the use of
expanded foam sealants and gaskets on all joints and corner
intersections. Leakage in the 23 test homes occurred where
it in the same places it does in frame houses: at the peak
of the cathedral ceilin gs, around window and door frames and
along the tops of walls. The study concludes air leakage in
well-built, modern log homes is not due to their log walls.
NAHB's Research Center conducted the second study for the
LHC in 1991. It showed the thermal mass of log walls does significantly
reduce energy use for heating in cold climates. It based its
conclusion on a comparison of the actual energy use of eight
log homes to the actual energy uses of eight well-insulated
foam houses during one winter. The number of houses were evenly
divided between upstate New York and Montana. The study also
compared the homes actual energy use to their predicted energy
consumptio n. The results led to the conclusion that log homes
were as energy efficient as the frame houses.
"What is significant here is the log walls' average R-values
was 44 percent lower than the frame walls' average R-value." says
Carter. "Clearly, we must conclude the thermal mass performance
of log walls is an advantage to log home owners."
Energy efficiency is just one of the
many topics covered in "An
American Dream, the Log Home," LHC's consumer booklet.
This 15-page, four-color booklet presents a complete review
of log home living as a lifestyle. For a copy and a list of
log home produce rs, send a $3 check or money order to: Log
Homes Council, National Association of Home Builders, 1201
15th Street, NW, Washington, DC 20005.
More than 50 of the nation's leading log home producers belong
to the LHC. It works to improve industry standards, increase
awareness of log construction as a method for building attractive
homes and overcome obstacles to log home ownership.
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