What is a radiant barrier in the attic?
Last updated · Energy & ventilation
Short answer: A radiant barrier is a reflective foil layer installed under the roof deck that blocks much of the heat a hot roof radiates into the attic. It works best in hot, sunny climates, especially when air conditioning ducts run through the attic. In cold or mild climates, adding more insulation usually pays off better.[1]
How does a radiant barrier work?
A radiant barrier works by reflecting radiant heat instead of absorbing it. On a summer day the sun heats the shingles and roof deck, and the underside of the deck radiates that heat down onto the attic floor insulation and any ducts. A shiny, low-emittance surface facing the attic sends far less heat downward. That keeps the insulation and ducts cooler, so less heat reaches the rooms below. It is different from insulation, which slows heat moving by conduction.
Where does a radiant barrier save the most energy?
A radiant barrier saves the most energy in hot-dry and hot-humid climates with strong sun, such as the Southwest, Texas, and Florida. A Building America brief from Pacific Northwest National Laboratory notes that radiant barriers can cut cooling costs roughly 8 to 12 percent in hot climates, and that they are seldom cost-effective in marine or cold climates.[1] Savings are larger when ducts and the air handler sit in the attic, because they are exposed to the radiant heat directly.
How is a radiant barrier installed?
A radiant barrier is installed in one of a few ways. During a reroof with new decking, the simplest option is roof sheathing with a foil face laminated to the underside, installed foil side down. In an existing attic, perforated foil sheeting can be stapled to the underside of the rafters or draped over them. The PNNL brief warns against laying the foil directly on top of attic floor insulation, because it can trap moisture and collects dust that ruins its reflectivity.[1]
Is a radiant barrier the same as reflective insulation?
A radiant barrier is not the same as reflective insulation, though the products look alike. A radiant barrier is a single reflective layer that faces an air space. Reflective insulation combines foil with bubbles, foam, or paper to add some R-value. Neither replaces the thick insulation on the attic floor, which the U.S. Department of Energy's Energy Saver guide describes as the main defense against heat flow through the ceiling.[2]
Should you add insulation or a radiant barrier first?
You should usually add insulation and seal air leaks before a radiant barrier. ENERGY STAR recommends sealing air leaks and bringing attic insulation up to recommended levels as a first step for most homes.[3] Once insulation is at the recommended level, a radiant barrier can add savings in hot climates. In a cold climate, the same money spent on more insulation usually does more.
Does a radiant barrier affect the roof?
A radiant barrier can slightly raise the temperature of the roof deck and shingles, since heat that would have radiated into the attic stays in the roof assembly longer. Studies have generally found the effect on shingle life to be small, but good attic ventilation still matters. Ask your roofer and the shingle maker whether a radiant barrier affects warranty terms, and make sure soffit and ridge vents stay clear.
When is the best time to add a radiant barrier?
The best time to add a radiant barrier is during a reroof that includes new decking, since foil-faced sheathing costs little more than plain sheathing and goes in with no extra labor. Adding foil in an existing attic is possible but involves working in a hot, cramped space, and the job is best left to an insulation contractor. Our guide on how roof type affects heating and cooling costs covers other options, including cool roofs.
What mistakes should you avoid with radiant barriers?
Common mistakes with radiant barriers include: - Laying foil on top of insulation, where dust and trapped moisture build up - Using non-perforated foil in a way that traps vapor - Blocking soffit vents or the ridge vent - Installing foil facing the wrong direction on sheathing - Expecting big savings in a cold climate Installed correctly, a radiant barrier is a modest, durable upgrade for hot homes.
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Frequently asked questions
Do radiant barriers work in winter?
They have little benefit in winter. Their main job is cutting summer heat gain in hot climates.
Can I use foil-faced sheathing when I replace my roof?
Yes, if decking is being replaced. Ask the roofer to quote foil-faced sheathing installed foil side down.
Is a radiant barrier worth it in a cold climate?
Usually not. More attic insulation and air sealing give better returns in cold climates.
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Sources
- PNNL Building America Solution Center: Installing a Radiant Barrier (PDF). basc.pnnl.gov/sites/default/files/case-studies/PNNL%20Perf%20Brief%20Radiant%20B
- U.S. Department of Energy: Energy Saver Guide (PDF). www.energy.gov/sites/default/files/2022-08/energy-saver-guide-2022.pdf
- ENERGY STAR: Seal and Insulate. www.energystar.gov/saveathome/seal_insulate
Sources checked November 4, 2026. Estimates are not quotes. Roofing, insurance, and legal details vary. Confirm with your contractor, insurer, or attorney.