Wood as thermal barrier

javier bolanos zeledon

LEEDuser Basic Member

192 thumbs up

March 15, 2011

Is it valid to use 1" wood as thermal barrier for the construction of roof insulation. We don't have easy access to commercial thermal barriers, we have to import them and the construction schedule is really tight. Best, Xavi

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Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Tue, 03/15/2011 - 15:33

Sounds like you are asking if it is OK to use wood as insulation? If so it is not much of an insulator at R1.25/inch.

javier bolanos zeledon

LEEDuser Basic Member

192 thumbs up

Tue, 03/15/2011 - 22:50

What is a valid R value for the thermal barrier then? Is it ok to put double layer of insulation in that part where the purling attaches to the metal deck?

Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

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Wed, 03/16/2011 - 17:42

Not sure I understand your questions. There is no minimum R-value per inch. By thermal barrier do you mean as continuous insulation? Appendix G in 90.1 provides guidance about the required U-factors and how they need to be calculated. The material itself is not the issue. The issue is meeting the insulating requirements.

javier bolanos zeledon

LEEDuser Basic Member

192 thumbs up

Wed, 03/16/2011 - 18:49

For a metal roof with single layer with thermal blocks detail, 90.1 states that you need to put a 1" thermal barrier (reference A.2.3.2.1 p.78 of Ashrae 90.1) to separate the metal roof from the insulation on each purling (reference p5-59 of the 90.1 user's manual) It does not say anything about the 1"thermal barrier, no R value or material or anything. So I was wondering what local material can I use to comply with the assembly or if I could put double layer of insulation on purlings so when crushed it will maintain it's rating.

Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Wed, 03/16/2011 - 19:24

Thanks for the specifics, they really help when trying to reply. Otherwise I am shooting in the dark. This section refers to an all metal building (like a Butler building). Not sure what is typically used - if I had to guess it would be some type of thick rubber - but it seems to me that wood would work in that situation for 90.1. Not sure I would trust it from a structural perspective as it could get wet and deteriorate but that is outside my expertise.