Radiant Barriers and Roof Shingle Temperatures
Because radiant barriers reflect the radiant heat rays that
strike them back in the opposite direction from which they came, modest concerns
have been raised about the possible increase in roofing temperatures and the
effect of increased temperatures on roof shingles.
According to the Reflective Insulation Manufactures Association's
independent study, a radiant barrier may cause an increase in shingle temperature
between 2-5 degrees Fahrenheit on a hot summer day. Given that shingle
temperature at that time is in the range of 160-190 degrees, this increase is
negligible and does not accelerate shingle degradation. Although roofing
manufacturers were concerned about shingle failure in the years when radiant
barriers were first used, it is no longer an issue. Roofing material
warranties are not affected by the installation of radiant barriers.
roof shingle temperature study for more details.
The Florida Solar Energy Center also conducted a study on
the use of radiant barriers under shingle roofs and found that properly installed
radiant barriers do not void the warranty for the shingles.
An interesting fact about roof temperatures and buildings
WITHOUT radiant barriers:
Without a radiant barrier in place, radiant energy from
the sun heats the roof decking and then radiates from the roof decking into
an attic and is absorbed by any existing heat absorbing insulation in the
attic. As the sun sets and the attic temperature begins to level itself
with the outdoor ambient temperature, the attic insulation is still radiating
the heat it has absorbed throughout the day.
In essence, the heat absorbing insulation is similar
to a hot piece of coal in your attic that is slowing emitting heat throughout
the early evening therefore, extending an increase in roof temperatures
into the early evening than if a radiant barrier had been in place.
Without a radiant barrier in place,
your existing insulation and roof stay hotter into the early evening causing
your air conditioning system to work harder and longer into the evening
to keep your home cool.