Glossary
Radiant barrier
A radiant barrier is a sheet of reflective material (usually aluminum on a backing) installed under the roof deck or over the attic rafters that reflects the sun's radiant heat instead of absorbing it. It lowers attic temperature in hot climates like Florida's. It works alongside insulation; it does not replace it.
What a radiant barrier is
Heat travels three ways: conduction (through a material), convection (through air) and radiation (like the heat you feel from a campfire without touching it). The roof, heated by the sun, radiates heat downward toward the insulation and the ducts sitting in the attic. Insulation with a good R-value slows conduction, but it absorbs that radiation and warms up.
A radiant barrier is a shiny, low-emissivity surface that reflects most of that radiation back. It needs an air gap on one side to work; pressed directly against another material, it stops reflecting and starts conducting.
Why it matters in Florida
It is a hot-climate technology: in the northern states it adds little, here it does. A Florida attic gets intense sun most of the year, and the air handler and its ducts are usually in that very attic. Lowering the attic temperature reduces the heat seeping through the ceiling and the heat the ducts absorb on their way to the rooms.
Its contribution is greatest when attic insulation is thin or when ducts run overhead. In a home with generous insulation and sealed ducts, the added benefit is smaller. That is why the usual priority order is: seal ducts, raise R-value, then evaluate the barrier.
Common mistake
Being sold a radiant barrier as a substitute for insulation or as “paint that insulates.” The barrier works against radiation; insulation works against conduction. Neither fixes leaky ducts. And interior reflective paints perform far below a properly installed aluminum sheet. We detail it in attic insulation in Florida.
Full guide: Attic insulation in Florida: blown-in, radiant barrier and what pays first →
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