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Radiant Barrier in the attic and wrapping the house with either our BTUFOIL tm Reflective Insulation or our
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$AVING$
From RIMA ( Reflective Insulation
Manufacturers Association ) ( Handbook #3 )
Complete document available for download here.
Source RIMA - Handbook3.doc
RADIANT BARRIERS
Physics of Radiant
Barriers
A radiant barrier
is a reflective/low-emittance surface, on or near a building component,
that
intercepts the flow of radiant energy to and from the building
component. It is, as the name suggests, a
barrier to
radiant heat movement, the same as a vapor barrier blocks water vapor
migration
and an air barrier stops air flow.
A radiant barrier can
be aluminum foil laminate, aluminized plastic film or a low emittance
coating. The only requirement is that
its surface must have low emittance and high reflectivity in the
infrared band
of the spectrum.
The aluminum foil
shields that are commonly inserted behind radiators in older houses are
radiant
barriers, blocking radiant heat transfer from the radiator to the
exterior
wall. The invisible glass coating in
low-E windows is also a radiant barrier.
It should be clearly
understood that although a radiant barrier reduces heat loss and gain
through
the building envelope, it is not an insulation material per se and has
no
inherent R-value.
Radiant Barrier Systems
(RBS)
A radiant barrier
system (RBS) is a building section that includes a radiant barrier
facing an
air space. An attic with a radiant
barrier on top of the mass insulation on the floor, or under the roof
is an
RBS. A vent skin wall with a radiant
barrier facing the vented air space is also an RBS.
The distinction
between a radiant barrier material and radiant barrier system is not
merely
academic. In an attic, the
effectiveness of a radiant barrier is significantly affected by the
amount of
attic ventilation. A vented attic with
a radiant barrier is a very different system from an unvented attic
with the
same radiant barrier.
TECHNICAL NOTE: The
generally
accepted definition of a radiant barrier system specifies that the
reflective
material face an open air space. The
idea is that a radiant barrier facing an enclosed air space is a
reflective
insulation with a measurable R- value.
