bldginsp
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# Posted: 6 Aug 2016 09:19pm
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I used just such a fire resistive slip sheet on my roof under metal and underlayment, and on the walls under Tyvek and Hardi. I used the Atlas brand FR-10 and FR-50. It's a fiberglass mesh with borate on it. It should be the first thing that contacts the wood, before any waterproofing. The FR-10 is very thin, the FR-50 much thicker (more borate). I used the 50 on the roof and the 10 on the exterior walls, reasoning that the walls already had Hardi but all the roof had was metal which conducts heat.
These slip sheets are not waterproofing layers, borate dissolves in water, so they have to go under the house wrap or roof underlayment. I think I spent around $250 for the three rolls I needed for a 300 sq ft cabin.
Could make the difference if the firefighters are stretched thin, as they usually are...
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