When the "Energy Crisis" of the 1970's sent
home heating and cooling costs soaring, demand for building
insulation rose right along with the prices of oil, gas, and
electricity.
As often (unfortunately) happens when demand for a product
increases suddenly and dramatically the promise of fast and
easy profits occasionally led to fast and easy sales and
marketing practices by some insulation sellers. Eventually
the claims and confusion in the insulation market became so
extreme the Federal Trade Commission instituted "The R-Value
Rule." This regulation placed clear limitations on the
claims and statements manufacturers and marketers can make
about insulation products and the energy savings they may
produce. The regulation is called "The R-Value Rule,"
because it is based on a mathematical term known to
engineers as "The R-Factor."
R-Factor is a measure of the ability of insulation material
to resist heat transfer. It's determined by placing
carefully prepared test specimens between two plates in a
laboratory apparatus and measuring heat flow through the
insulation. "R-Value" is the R-Factor of the insulation
multiplied by the amount of the material.
If insulation has an R-Factor of 3.8, and there are 3.5
inches of insulation between the warm side and the cool side
of the assembly, the R- Value of the insulation in the
system is 13.3. The R-Value Rule is a good regulation that
has significantly reduced misrepresentation and outright
fraud in the insulation industry. It's one of the most
important and successful consumer protection regulations
ever enacted by the U.S. Federal Government.
Consumers often assume The R-Value Rule will automatically
lead them to the insulation product with the greatest energy
savings when it's installed in a building. Unfortunately,
this isn't the case. In the real world of buildings things
are a bit more complicated. In fact, they're a lot more
complicated.
R-Value is a very accurate and reliable expression of how
insulation materials perform in a laboratory apparatus. But
people don't live in laboratories. They live in homes with
real walls and ceilings, and in the real world of buildings
R-Value is only one factor in the actual performance of
insulated building assemblies.
Scientists and engineers refer to building systems that
separate the interior of a structure from the ambient
environment as the" building thermal envelope." Many factors
affect the energy efficiency of the thermal envelope. These
include:
- Total R-Value of all system
components.
- Air Infiltration due to leakage
through gaps in the system.
- Air infiltration due to permeability
of system elements.
- Convective flows within insulated
systems.
- Thermal bridging across the building
envelope.
- Thermal mass of building components.
R-Value is important, but building
scientists know that focusing on R-Value to the exclusion of
all other factors can result in disappointment with thermal
envelope performance. It's known, for instance, that thermal
bridging can reduce the actual energy efficiency of a wall
by up to 50 percent. U.S. scientists have proven that
convective flows in very light density attic insulation can
reduce its performance by more than 40 percent under winter
conditions. Canadian researchers have reported a similar
effect in walls.
Air leakage and gaps at the interface between framing
members and insulation is harder to quantify, but in a
letter to Home Energy magazine an experienced, prominent
thermo graphic inspector stated:
Of the hundreds of buildings I have inspected with infrared
thermography I have yet to see even one fiber glass job that
doesn't suffer some reduced thermal performance. Often the
degradation is substantial, especially under windy
conditions.
In the winter of 1989-90 The University of Colorado School
of Architecture and Planning putt wo insulation materials to
the test. CU researchers built two identical test
structures. One structure was insulated with R-19 fiber
glass batts in the walls andR-30 batts in the ceiling. The
walls of the other structure were insulated with cellulose
wall spray, and R-30 of loose-fill cellulose was blown in
the ceiling.
Although the nominal R-value of the insulation in the walls
and ceilings of the structures was essentially identical,
their energy performance was very different. Blower door
tests showed that cellulose tightened the structure 36 to 38
percent more than fiber glass. The cellulose insulated
structure was seven degrees warmer than the fiberglass
structure after a nine-hour overnight heat loss test. Most
important, after three weeks the cellulose-insulated
structure had used 26.4% less energy to heat than the fiber
glass structure.
The CU researchers concluded cellulose performs as much as
38 percent better than fiberglass. "The performance
advantage of cellulose intemperate climates appears to be
about 26%," they wrote." This benefit would become more
significant in more severe climates." The Colorado data
gives scientific support to the long held belief that "R"
for "R" cellulose out-performs other fiber insulation
materials.
Other surveys of energy consumed to heat actual homes in
Pennsylvania, Kansas, Massachusetts, and the United Kingdom
have shown cellulose performance superiority ranging from
20% to 33%.Extensive and expensive air sealing measures must
be used for fiber glass buildings to approach the tightness
of buildings insulated with cellulose.
The extra expense may yield few benefits. In the
Massachusetts survey the cellulose insulated building still
consumed 32% less energy for heating than buildings
insulated with fiber glass, even after extensive air sealing
of all the buildings was done.
This real world performance difference does not mean
consumers and specifiers should ignore R-Value. R-Value is
important to insure that buyers receive all the insulation
they contract for. It's also important in comparing prices
among vendors proposing to supply the same type of
insulation.
R-Value is less useful for comparing different types of
insulation. For instance, very expensive high density R-15
mineral fiber batts intended for use in walls with
conventional 2 X 4 framing are available. They achieve this
"laboratory R-value" by packing three times more glass into
batts the same thickness as the R-11 batts that have been
standard for many years. The nominal R-Value of cellulose
insulation in the same wall would be R-13 to R-13.5.
The Colorado data suggests that to obtain an estimate of the
relative real world performance of the two materials, the
R-Value of the cellulose insulation should be increased by
26 to 38 percent. On this basis the R-13 cellulose wall
insulation would be expected to deliver performance
equivalent to R-16.3 fiber glass batts. No such batts are
available.
The shortcomings of R-Value as a measure of real world
insulation performance are recognized by the building
community. The Building Environment and Thermal Envelope
Council of the National Institute of Building Science (BETEC)
has received a number of research proposals to develop
practical methods for measuring the energy-saving
performance of total building thermal envelope systems and
the relative performance of different insulation materials.
Until this research is completed buyers and specifiers must
remember that "R" for "R" all insulation is not created
equal. In the real world of buildings it's necessary to
install more "Rs" of fiberglass insulation or use expensive
air sealing techniques to achieve the energy-conservation
performance of cellulose and other insulation materials less
susceptible to air infiltration, internal convection, and
installation defect problems than mineral fiber products.
Conclusion: R-Value is an important aid to consumers when
comparing proposals and specifications for different brands
or suppliers of the same type of insulation. It is less
useful when comparing different insulation materials.
R-for-R all insulation is NOT created equal! |
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