How are thermal (fire) barriers installed over foam insulation in a crawlspace?

Question

I will soon be sealing my crawlspace with plastic sheeting across the floor and up the concrete walls. I plan on then adding rigid foam insulation.

My reading of the Residential Code is that I will need to install a thermal barrier over the rigid foam board to add protection against ignition. The layers of material are:

earth---concrete---plastic sheeting---foam board---thermal barrier---crawlspace air

Typically, a thermal barrier is provided by 1/2" gypsum board. My issue is that this is a crawlspace. I am not planning on installing studs to support wall board.

• Do I need to install the barrier in a crawlspace?
• What would I use as a barrier since I don't have studs to hange wall board on?
• Is there an alternative that I am missing?

Related questions:

• Do basement walls with metal framing and foam insulation require fireblocking and draftstopping?
• How can I install r-max insulation on the interior side of a cinderblock wall?
• Should I encapsulate my crawl space?

Answer 1

Do I need to install the barrier in a crawlspace?

Yes you need to install the barrier regardless of where it is.

What would I use as a barrier since I don't have studs to hang wall board on? Is there an alternative that I am missing?

You don't need studs to install drywall. You could install furring strips and then attach the drywall to this. You can even get XPS foam with channels for the furring strips cut out so that you don't add any extra depth to the wall.

Answer 2

Confirm this with your county's building permits folks, but there are now several lines of Polyiso foam board insulation that are rated for use without a barier. Check out Dow Thermax, Hunter Xci 286, and Rmax Thermasheath XP.