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diyatx 12-08-2012 06:10 PM

Thermal barrier for XPS foam board
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I used 1/2" pink XPS foam board as insulation in a folding attic ladder. The instructions say it's flammable and thus should not be exposed in any application and recommends using a thermal barrier. Not having any luck finding such a barrier. Can someone point me to what I should order?

(BTW, I wish the chatroom would allow me to correct the subject line, but no luck. "Battier" it remains. Oops)

woodworkbykirk 12-08-2012 07:00 PM

it has to be covered by drywall..
1/2" drywall really doesnt do much as a thermal barrier, 1" is the starting point

diyatx 12-08-2012 07:28 PM

Well, in that light, any code-approved fireblocking material would do (3/4" particle board, 1/2" drywall, 1/4" cement board); it doesn't need to be drywall. I should have been clearer. There's little clearance between the steps and the foam board, so I'm basically asking if anyone knows of a *thin* (1/8" or less) material that will act as a thermal barrier.

Gary in WA 12-08-2012 08:55 PM

The thermal barrier is the plywood panel facer. An ignition barrier may be needed instead, if you meet all requirements listed here:

Or, use the manufacturer's literature, #4.2.1- Attics:

Or just use R-Max (foil-faced PIC board) accepted by most Building Departments;

check with local AHJ.


diyatx 12-09-2012 08:14 AM


Originally Posted by GBR in WA (Post 1069204)
The thermal barrier is the plywood panel facer. An ignition barrier may be needed instead, if you meet all requirements listed here...

Thanks, Gary. If I'm reading this material right, the IRC wants at least an ignition barrier in attic spaces and reveals the thin solution I was looking for (1/64" thick corrosion-resistant steel). Owens Corning, however, says I don't need to worry about it.

Interestingly, the R-Max literature is less forgiving than OC's. Its recommendation is in line with the IRC: put an ignition barrier on the interior side.

My understanding is that the IRC yields to manufacturer installation instructions, so I'm probably going to follow the OC literature and leave the pink foam exposed. I've called the building/inspection dept in the past and found muted interest in answering small-time questions like this. Because I'm following manufacturer instructions, I think I can let this rest and save myself a bunch of calls.

Thanks again!

Gary in WA 12-09-2012 03:01 PM

You're welcome, we are here to help DIY! Additional useful information:


Windows on Wash 12-10-2012 07:55 AM


Use foil faced ISO and you should be fine.

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