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Flat roof, non vented — What about furred space for slope?

I am building a non-vented flat roof in CEC zone 8/ DOE zone 3-92705. Roof structure will be structural sheathing on 12" I-joist. For slope, sheathing over 2x furring strips (1/4"/12"). I have read all the posts about various ways to insulate.

If the actual roof is something like a 2-ply SBS membrane and the insulation under the structural sheathing is a closed-cell flash-and-batt system, should I worry about the spaces between the 2x furring strips used over the structural sheathing for slope?

This space will not be vented. Will this space trap moisture?

Asked by keith messick
Posted Fri, 03/14/2014 - 10:33
Edited Fri, 03/14/2014 - 11:40

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Keith,
Q. "If the actual roof is something like a 2-ply SBS membrane and the insulation under the structural sheathing is a closed-cell flash-and-batt system, should I worry about the spaces between the 2x furring strips used over the structural sheathing for slope?"

A. No.

Q. "This space will not be vented. Will this space trap moisture?"

A. No. But make sure that the materials are all dry on the day when your spray foam contractor shows up.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 03/14/2014 - 11:36

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