What does a radiant barrier do?

It reflects infrared heat from the hot roof deck back outward instead of allowing it to radiate down into the attic, which helps reduce cooling load on hot days.

Is a radiant barrier the same as insulation?

No. A radiant barrier reduces radiant heat transfer, while insulation slows conductive heat flow. Homes often benefit from both, and a radiant barrier cannot substitute for missing attic insulation.

Does a radiant barrier really lower attic temperatures?

Yes, in the right climate and installation. It can reduce radiant heat from a hot roof deck into the attic, often lowering peak temperature by 20 to 30 degrees Fahrenheit. The effect is strongest when the reflective face stays clean and faces an open air space.

Can I install a radiant barrier over existing insulation?

Some reflective products can be added in an attic, but simply placing foil on top of existing insulation is not the same as a properly detailed radiant barrier. Placement, air space, and moisture behavior all matter.

How long does a radiant barrier last?

The reflective layer can last many years if it stays intact and reasonably clean. Performance drops when the foil is torn, heavily dust-coated, or covered by later work. Most barriers last until a reroof, remodel, or damage event disturbs them.

Radiant Barrier — Reflective Attic Insulation Explained

A radiant barrier is a reflective foil or foil-faced building material installed in an attic or roof assembly to reflect radiant heat away from living spaces and reduce cooling load.

Radiant Barrier diagram — labeled parts and installation context

What It Is

Radiant barriers work by reflecting infrared radiation rather than slowing conductive heat flow the way bulk insulation does. A radiant barrier surface has an emittance of 0.05 or less, meaning it reflects approximately 95 percent of the radiant heat striking it. The reflective face must face an air gap of at least 3/4 inch to be effective; a foil face buried against another material provides little benefit because it cannot reflect energy without an open space.

In hot climates, a properly installed radiant barrier can lower peak attic temperatures by 20 to 30 degrees Fahrenheit and reduce the cooling load on air conditioning equipment by 5 to 10 percent. The Department of Energy considers radiant barriers most effective in IECC climate zones 1 through 3, where cooling costs dominate energy bills.

Types

Common types include foil-faced roof sheathing panels, also called radiant barrier sheathing or RBS, that combine structural OSB with a factory-applied foil face on the attic side. Perforated foil laminates are stapled across the underside of rafters as a retrofit, and the perforations allow water vapor to pass through to reduce condensation risk in mixed-humidity climates.

Multi-layer reflective products combine one or two radiant layers with lightweight polyethylene bubble or fiber insulation to add a small amount of conductive resistance alongside the radiant benefit. Spray-applied radiant barrier coatings use aluminum flake in a liquid carrier applied directly to the underside of roof decking, though their long-term performance can degrade as dust accumulates on the textured surface.

Where It Is Used

Radiant barriers are used in attics, cathedral ceilings, metal buildings, and roof assemblies where solar heat gain is a primary concern. They are most effective in hot or mixed climates and are often paired with conventional attic insulation and ventilation. In new construction in southern states, foil-faced roof sheathing is frequently specified because it adds radiant protection at minimal additional cost during framing.

Metal buildings benefit significantly from radiant barriers because uninsulated metal roofing radiates intense heat into the interior. In these applications, a draped radiant barrier below the purlins creates an air gap between the metal panels and the reflective surface, substantially reducing interior temperatures.

How to Identify One

Look in the attic for a shiny foil face attached to the underside of the roof framing or integrated into roof deck panels. It resembles foil insulation, but the key distinction is that the reflective surface faces an open air gap rather than being buried between layers. Radiant barrier sheathing is identifiable from the attic as OSB panels with a silver or gold foil laminated to the interior face.

Retrofit foil barriers appear as sheets of foil stapled to the bottom edges or faces of rafters, hanging slightly below the roof deck. The material will feel thin and flexible compared to rigid foam insulation, and the foil surface will be highly reflective when clean.

Replacement

Replacement is needed when the barrier is torn, heavily dust-coated to the point where the reflective surface is no longer shiny, contaminated by blown-in insulation that was incorrectly installed over it, or removed during reroofing or attic remodeling. A radiant barrier covered in a thick layer of dust loses most of its reflective performance because the dust absorbs and re-emits radiant heat rather than reflecting it.

When evaluating comfort issues, contractors usually inspect ventilation, air sealing, and insulation depth alongside the radiant barrier condition, since all four elements work together as a system. Replacing only the radiant barrier without addressing poor air sealing or insufficient insulation depth will yield limited improvement.