Dual Plane Attics have two 'planes' of
insulation.
There is the normal R-30 insulation on
the ceiling. Then double/bubble, foil-foil is added to the
rafters. In new construction, full soffit venting and full ridge
venting is also added.
The science behind the concept.
Half the sun's energy is radiant.
Arizona gets 40% more radiant energy than Miami. Arizona gets more
radiant energy because it's a 'dry heat'. 95% of greenhouse gas is
water vapor and Arizona doesn't get much.
If the radiant energy is reflected, most
of it just goes away. Some of the energy is left behind in the
radiant barrier and is 'emitted' as heat.
In Arizona there is an additional
challenge; dust. Arizona dust is unique enough to have a
scientific denotation. If dust covers a radiant barrier, it loses
it's radiant barrier properties.
Reflectix, Inc.'s double/bubble,
foil-foil is one product that addresses all the scientific issues.
It is a sandwich of two layers of a 97% radiant barrier with two rows of
closed cell bubbles in the middle. If the top layer of radiant
barrier gets dusty, the second layer will still reflect 97% of the
radiant energy. The double/bubble is a 'relative R-17'.
'Relative' because insulation loses
efficiency the hotter it gets. In a simple test, R-30 and
double/bubble, foil-foil were placed in the sun. After 6 hours,
the heat transfer was about the same. The surface of the R-30 got
to 154 degrees. The double/bubble remained cooler than the deck
temperature of 122 degrees.
WHAT THIS ALL MEANS TO YOU is that the
attic remains ambient temperature or below.
That means that the normal insulation of
the ceiling is more effective and doesn't have to work as hard.
Real world testing in Arizona documented
a 25% savings in air conditioning.
