Radiant Barrier Air Gap

Ask The Expert – Q & ACategory: Building CodesRadiant Barrier Air Gap
RIMA Expert Staff asked 6 months ago

Hello, I am speaking with two suppliers of two different radiant barriers. I am learning from them that it meets the CA acceptable cool roof alternative for compliance with both the prescriptive and performance methods for energy compliance as described in ES 150.2(b)1H. Energy Standards 150.2(b)H1 (prescriptive)and Table 150.2-B (performance).

My concern is they tell me I can install this product on a roof deck without a 3/4 or 1″ air gap between the deck, vapor barrier and roofing material, meaning direct contact between deck and roofing materials. I have learned in the past that radiant barriers need an air cap of at least 3/4″ of an inch to perform.

I am estimating on three different residential buildings to show the local building departments that these products can work to allow an alternative other than the more costly alternatives here in zones 11 & 12 CA.

Can you possibly supply me with a correct approach or any info possible to do this approval process?

1 Answers
Best Answer
RIMA Expert Staff answered 6 months ago

The correct installation of a radiant barrier is on the face of roof joists or trusses which would provide a significant air space between the underside of the roof and the radiant barrier.  You can also install between the joists allowing 3/4” to 1” air space between the radiant barrier and the underside of the roof.  You are correct that radiant barriers need air spaces in order to work.  It is also a good idea to allow for convection above the radiant barrier by leaving a gap at the ridge of about 6”.  If there are no eave openings, leave a 6” gap there as well so that there would be air flow from bottom to the ridge