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Alternative-Heating-Info.com
Radiant Attic Barriers
Research done by the Florida Solar Energy Center (FSEC) shows an attic radiant barrier
can save 10% to 15% on the heating and cooling portion of electricity costs in a typical
Florida home. This would translate to annual savings of 3% to 6% on the entire electric bill.
Although it's widely recognized that a radiant barrier system will save on cooling costs,
radiant barriers are not generally considered a good application in climates where home
heating is dominant. In this respect, the FSEC states "Although not as significant, heating
savings may also accrue from the use of radiant barriers."
Somewhat more enthusiastic about potential heating savings from radiant barriers is Prof.
Charles Shabica of Northeastern Illinois University. He concluded after independent testing
that "In the frame house test, IR (heat loss) emittance is measurably lower on the side of
the house with the radiant barrier."
Despite these encouraging statements, a homeowner in Maine should not expect as much
in total energy savings from a radiant barrier as a homeowner in South Carolina.
The installation of an attic barrier is relatively simple making it an ideal DIY project. Basically
you have two installation choices: Over the attic floor, or between the rafters supporting
the roof. Of the two, over the attic floor is the easiest. Simply roll out the sheets, shiny side
up, from one end of the attic to the other overlapping the sheets as you go along.
No stapling is required because you want the reflective sheets to float freely above the
insulation allowing an air space underneath the barrier as well as above. If the barrier is
compressed against the underlying layer of insulation it will lose its effectiveness.
One concern frequently voiced with "over the attic floor" installations is dust accumulating
on the surface of the barrier and degrading its effectiveness over time. But opinions vary
depending on the source. Here are two conflicting opinions from separate U.S. government
agencies.
According to the National Bureau of Standards, U.S. Dept. of Commerce, "Thin layers of
dust readily visible to the eye do not cause very serious lowering in the reflecting power.
The appearance of the surface is not a reliable guide as to its reflectivity for radiant heat.
Foil which appears dark or discolored may have lost little in insulating value if the surface
film is thin."
Now let's hear what the Dept. of Energy has to say: "When radiant barriers are newly
installed, some testing shows that the attic floor application will work better than the roof
applications. As dust accumulates on the attic floor application, its effectiveness will
gradually decrease. After a long enough period of time, a dusty attic floor application will
lose much of its effectiveness. Predictive modeling results, based on testing, suggest that
a dusty attic floor application will lose about half of its effectiveness after about one to ten
years."
I would tend to side with the Dept. of Energy, but some attics just aren't as dusty as
others; it's really up to you. In any case, take a minute to spend some quality time with
your attic and have a look around. You may have forgotten how much stuff is up there
rendering an over the floor installation ineffective as well as impractical.
If you decide to proceed with the over the floor application, purchase a perforated barrier
especially designed to allow moisture to pass through, and take care not to cover kitchen
and bathroom vents or recessed lights.
can save 10% to 15% on the heating and cooling portion of electricity costs in a typical
Florida home. This would translate to annual savings of 3% to 6% on the entire electric bill.
Although it's widely recognized that a radiant barrier system will save on cooling costs,
radiant barriers are not generally considered a good application in climates where home
heating is dominant. In this respect, the FSEC states "Although not as significant, heating
savings may also accrue from the use of radiant barriers."
Somewhat more enthusiastic about potential heating savings from radiant barriers is Prof.
Charles Shabica of Northeastern Illinois University. He concluded after independent testing
that "In the frame house test, IR (heat loss) emittance is measurably lower on the side of
the house with the radiant barrier."
Despite these encouraging statements, a homeowner in Maine should not expect as much
in total energy savings from a radiant barrier as a homeowner in South Carolina.
The installation of an attic barrier is relatively simple making it an ideal DIY project. Basically
you have two installation choices: Over the attic floor, or between the rafters supporting
the roof. Of the two, over the attic floor is the easiest. Simply roll out the sheets, shiny side
up, from one end of the attic to the other overlapping the sheets as you go along.
No stapling is required because you want the reflective sheets to float freely above the
insulation allowing an air space underneath the barrier as well as above. If the barrier is
compressed against the underlying layer of insulation it will lose its effectiveness.
One concern frequently voiced with "over the attic floor" installations is dust accumulating
on the surface of the barrier and degrading its effectiveness over time. But opinions vary
depending on the source. Here are two conflicting opinions from separate U.S. government
agencies.
According to the National Bureau of Standards, U.S. Dept. of Commerce, "Thin layers of
dust readily visible to the eye do not cause very serious lowering in the reflecting power.
The appearance of the surface is not a reliable guide as to its reflectivity for radiant heat.
Foil which appears dark or discolored may have lost little in insulating value if the surface
film is thin."
Now let's hear what the Dept. of Energy has to say: "When radiant barriers are newly
installed, some testing shows that the attic floor application will work better than the roof
applications. As dust accumulates on the attic floor application, its effectiveness will
gradually decrease. After a long enough period of time, a dusty attic floor application will
lose much of its effectiveness. Predictive modeling results, based on testing, suggest that
a dusty attic floor application will lose about half of its effectiveness after about one to ten
years."
I would tend to side with the Dept. of Energy, but some attics just aren't as dusty as
others; it's really up to you. In any case, take a minute to spend some quality time with
your attic and have a look around. You may have forgotten how much stuff is up there
rendering an over the floor installation ineffective as well as impractical.
If you decide to proceed with the over the floor application, purchase a perforated barrier
especially designed to allow moisture to pass through, and take care not to cover kitchen
and bathroom vents or recessed lights.
When you install the barrier between, or along the rafters, the gable ends should also be
covered. If the attic roof extends over the garage, the Dept. of Energy recommends
extending the barrier by 8 feet over the garage to achieve the same effect as covering the
gable end. However, covering the gable ends is not necessary if the barrier is installed
over the attic floor.
Radiant barrier foil is not insulation per se and therefore has no inherent 'R' value rating.
Prices for radiant barriers vary by function and durability (tensile strength). Perforated
barriers, and high tensile strength barriers (80.4 lb/in) both sell for around $0.15 per
square foot. Standard strength barriers (14.1 lb/in) are slightly less at $0.12 per square
foot.
The cost an attic barrier can be further reduced with the new Energy Tax Credits. The
maximum credit is now 30% of the cost of the material up to $1,500. Installation is not
covered.
covered. If the attic roof extends over the garage, the Dept. of Energy recommends
extending the barrier by 8 feet over the garage to achieve the same effect as covering the
gable end. However, covering the gable ends is not necessary if the barrier is installed
over the attic floor.
Radiant barrier foil is not insulation per se and therefore has no inherent 'R' value rating.
Prices for radiant barriers vary by function and durability (tensile strength). Perforated
barriers, and high tensile strength barriers (80.4 lb/in) both sell for around $0.15 per
square foot. Standard strength barriers (14.1 lb/in) are slightly less at $0.12 per square
foot.
The cost an attic barrier can be further reduced with the new Energy Tax Credits. The
maximum credit is now 30% of the cost of the material up to $1,500. Installation is not
covered.
The second installation option is with
the reflective side facing down from
the rafters.
Diagram #1 illustrates between the
rafters. Diagram #2 illustrates rafter
to rafter horizontally across the attic.
Of the two, across the rafters would
obviously be easier to implement.
In either case make sure the shiny
surface is facing down towards the
attic floor.
Now you have to be asking yourself,
"How can the foil side work if it is
facing downwards?"
It may seem counterintuitive, but a
radiant barrier works just as well
with the reflective side facing toward
the roof or away from it.
This is because a radiant barrier not
only REFLECTS INFRARED ENERGY, it
also does not EMIT RADIANT HEAT.
These two qualities are known as
Reflectivity and Emissivity and work
together as one; not exclusive of
each other.
the reflective side facing down from
the rafters.
Diagram #1 illustrates between the
rafters. Diagram #2 illustrates rafter
to rafter horizontally across the attic.
Of the two, across the rafters would
obviously be easier to implement.
In either case make sure the shiny
surface is facing down towards the
attic floor.
Now you have to be asking yourself,
"How can the foil side work if it is
facing downwards?"
It may seem counterintuitive, but a
radiant barrier works just as well
with the reflective side facing toward
the roof or away from it.
This is because a radiant barrier not
only REFLECTS INFRARED ENERGY, it
also does not EMIT RADIANT HEAT.
These two qualities are known as
Reflectivity and Emissivity and work
together as one; not exclusive of
each other.
| Diagram #1 Between the rafters vertical installation |
| Diagram #2 Rafter to rafter horizontal installation |
The attic radiant barrier was originally designed
as a means to reduce attic heat in southern
climates where air conditioning is prevalent.
Lowering the temperature in your attic
suppresses heat gain on lower floors and in
turn reduces the cooling load on the air
conditioning system.
A reduction in the cooling load means the air
conditioner requires less energy to provide the
same amount of cooling; saving you money.
as a means to reduce attic heat in southern
climates where air conditioning is prevalent.
Lowering the temperature in your attic
suppresses heat gain on lower floors and in
turn reduces the cooling load on the air
conditioning system.
A reduction in the cooling load means the air
conditioner requires less energy to provide the
same amount of cooling; saving you money.
| Radiant foil barrier |