# Thermal barrier for XPS foam board



## woodworkbykirk (Sep 25, 2011)

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


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## cortell (Nov 27, 2010)

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.


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## Gary in WA (Mar 11, 2009)

The thermal barrier is the plywood panel facer. An ignition barrier may be needed instead, if you meet all requirements listed here: http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_3_sec016_par007.htm

Or, use the manufacturer's literature, #4.2.1- Attics: http://commercial.owenscorning.com/assets/0/144/172/174/5deb06d2-43b4-44b2-b4ec-20579af27e5d.pdf

Or just use R-Max (foil-faced PIC board) accepted by most Building Departments; http://www.rmaxinc.com/downloads/DataSheets/rmp3.pdf

check with local AHJ.

Gary


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## cortell (Nov 27, 2010)

GBR in WA said:


> 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!


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## Gary in WA (Mar 11, 2009)

You're welcome, we are here to help DIY! Additional useful information: http://www.ncfi.com/Insulation/uplo...e Criteria and the Building Codes SF0608L.pdf

Gary


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## Windows on Wash (Aug 30, 2011)

+1

Use foil faced ISO and you should be fine.


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