One of the most misunderstood parts of installing a radiant barrier is the role of the air gap. People often assume the foil itself is doing all the work, but the reality is that a radiant barrier only works effectively when it faces open air space.

Without that space, you lose the reflective benefit.

Fortunately, many modern roofing systems already create this air gap naturally, especially metal roofing and tile roofing installations. That makes adding RoofingFoil™ an easy and highly effective upgrade during construction or reroofing.

Why the Air Gap Matters

Radiant heat moves differently than conductive heat. Instead of traveling through direct contact, radiant heat travels in waves across open space. This is the same type of heat you feel standing near a fire or sitting in direct sunlight.

A radiant barrier works by reflecting that radiant energy away before it can transfer into the structure below.

However, this reflection can only happen if there is an adjacent air space.

If the foil is sandwiched between any 2 materials (no matter how light or airy they are), heat simply transfers through direct contact and the reflective surface cannot function properly as a radiant barrier. In other words, the foil needs room to “see” an open air space so it can reflect radiant heat instead of absorbing and conducting it.

The Minimum Recommended Air Gap

For RoofingFoil™ installations, the recommended minimum air gap is ½ inch.

Larger air gaps are perfectly acceptable and are commonly used in many roofing assemblies. What matters is that the space does not get compressed below that ½-inch minimum.

This is one reason RoofingFoil™ pairs so well with batten systems, purlins, furring strips, and tile roof assemblies. These systems naturally create an air cavity beneath the roofing material while also providing a convenient attachment structure for the roof itself.

Metal and Tile Roofs Naturally Create Ideal Conditions

Many standing seam metal roofs, stone coated steel roofs, and tile roofing systems already include built-in air spaces as part of their design.

Examples include:

• Batten and counter batten systems
• Purlin-framed metal buildings
• Tile roofs installed over battens
• Spanish style curved tiles
• Furring strip systems beneath roofing panels
• Raised roofing assemblies designed for drainage or ventilation

Because these systems already create the required spacing, adding RoofingFoil™ often becomes a very straightforward decision. The air gap needed for radiant barrier performance is already there, so the foil can immediately begin reflecting radiant heat away from the roof deck and attic space.

Rather than allowing the hot underside of the roofing material to radiate heat directly into the structure, RoofingFoil™ reflects up to 97% of that radiant heat energy back toward the air space.

Can This Be Placed Directly Under Shingles?

No, because radiant barrier foil must have an air space on at least one side in order for it to work. In the case of a shingled roof, the foil would be sandwiched between asphalt shingles and the roofing deck/underlayment. In this set up, there is no air space, so the aluminum radiant barrier layer will not be effective in any way.

The only way to make a radiant barrier compatible with a shingle style roof is to create an air space (ie. a double-deck system) or install it below the decking, draped between the rafter cavities, or by using a foil-faced OSB decking, where the foil faces down toward the open air attic space.

Can I Add Foam Board Over the Radiant Barrier Layer?

No, just like the example above, doing this would sandwich the radiant barrier foil between two materials, rendering it ineffective at blocking radiant heat. You must have an air space on at least one side in order for it to work so you cannot add a foam layer, or any other layer (besides the battens if using) on the foil surface.

Does the Air Gap Need to Be Vented?

This is another area where people get confused.

The air gap does not have to be vented in order for the radiant barrier to work.

A sealed or “dead” air space can still provide excellent radiant barrier performance because radiant heat transfer is still occurring across that cavity. As long as the foil faces open air space, it can reflect radiant energy effectively. That said, ventilation can provide additional benefits in many roofing systems.

When the air cavity is vented, moving air can help:

• Remove accumulated heat from beneath the roofing
• Reduce roof deck temperatures further
• Help dry incidental moisture or condensation
• Improve overall roof system durability

This is why many premium roofing systems combine both ventilation and radiant barrier technology together. The ventilation helps carry heat or moisture away while the radiant barrier reduces how much radiant energy enters the structure in the first place.

A Smarter Roofing Assembly

The effectiveness of a roofing system is not determined by the roofing material alone. The space beneath the roof plays a major role in controlling heat transfer and overall comfort inside the home or structure.

By combining:

• Proper air spacing
• A reflective radiant barrier
• Ventilation where appropriate
  

you create a roofing assembly that performs far better than the roofing material alone.

Because so many metal and tile roofing systems already include the necessary air gap, incorporating RoofingFoil™ is often one of the simplest and most effective upgrades available for reducing radiant heat transfer and improving energy efficiency.