Does polyisocyanurate roof insulation on top of a concrete or metal deck need to be included in the documentation of the low-emitting materials insulation category?
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David Posada
Integrated Design & LEED SpecialistSERA Architects
LEEDuser Expert
1976 thumbs up
December 23, 2020 - 5:10 pm
Allen - Possibly, but in some scenarios probably not...
For v4.1 the credit language says the building interior is "everything within the waterproofing membrane" so in some roof assemblies the waterproofing membrane could be just a membrane roof above the insulation, which would make the insulation be on the "interior." In some other assemblies, such as Joe Lstiburek's "Perfect wall/ roof" (see buildingscience.com) the primary weather resistant barrier can be in board of the insulation, putting the insulation on the exterior.
The version 4 language gives a little more guidance:
"The building interior is defined as everything within the waterproofing membrane. The building exterior is defined as everything outside and inclusive of the primary and secondary weatherproofing system, such as waterproofing membranes and air- and water-resistive barrier materials."
If you have a good air barrier in-board of the insulation, you could make a case that the insulation is isolated from the interior. In that scenario the insulation might be between the primary and secondary components of the weatherproofing system, and so could be "inclusive" of that exterior assembly. In some cases the polyiso might be acting as an air barrier itself (if the joints are taped) so you might make the case that it's "inclusive" of the weatherproofing system.
Getting back to the intent, the main issue is how effectively the polyiso is isolated from the interior. To your question, a concrete deck makes a pretty good air barrier when penetrations are sealed, so that seems reasonable. A steel deck by itself may be less effective an air barrier given the many fastener penetrations, but many recommended roofing details include an air/ vapor barrier between the metal deck and the insulation.
Hope that helps – sounds like a good question for a LEED coach (technical customer service) especially if you have a registered project. If you have an upcoming submission, you can also schedule one pre-review phone call to clarify questions like that.
Allen Cornett
Sustainable ConsultantINSPEC Sustainability Group LLC
49 thumbs up
December 24, 2020 - 11:09 am
Thank you for your thoughts. I had been going back and forth with my own.
Catherine Blakemore
Architect, LEED AP BC+DHOLT Architects
31 thumbs up
June 11, 2021 - 5:59 pm
If the roofing membrane is the primary weatherproofing system at the roof, does the roofing membrane adhesive need to comply or is it
1) exempt because it actually part of (integral to) the weatherproofing system, or
2) does it have to comply because it is on the inteior side of the weatherproofing system?
I would agree that anything below the roof membrane adhesive layer would have to comply, just not sure about the adhesive used to adhere the acutal membrane in-place.
As always, any guidance is appreciated.