polyisocyanurate roof insulation

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.  

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.  

David's observations about "inclusive" and Catherine's question reminded me of the following GBCI inquiry and reply I received for a Firestone EPDM system.   From the reply I interpret that any part of the roofing system including primer and adhesive applied to deck to be part of the weatherproofing system (and thus not subject to VOC Content or Emissions thresholds).  And the reply did not request discernment of airtightness of the underlying deck.  Your mileage may vary. "Thank you for your email regarding EQ credit Low-emitting Materials requirements for your LEED v4 project. Yes, the primer used with the EPDM Roof may be excluded from the calculations as part of the weatherproofing system. ORIGINAL INQUIRY: v4.1 Low-Emitting Materials - Adhesives and Sealants: To install a Firestone EPDM roof we are first applying Firestone's V-Force Vapor Barrier Membrane (polyethylene backed with modified bitumen adhesive) over concrete deck. However, a primer must first be applied to clean and prep deck to properly adhere the membrane. Proactively, we have considered switching from Firestone's SA Solvent Based Primer with VOCs above SCAQMD Rule 1168 (2017) limit, to their SA Water Based Primer which is well below 1168 limit. However, we contacted Firestone, who does not test for CDPH v1.2-2017 because they consider their products part of the weatherproofing system, and not affecting IAQ. As the primer is critical to adhering membrane to deck, we follow this logic. v4 BD C Ref Guide, Pg. 690 bounds "building exterior" by "weatherproofing system" while "building interior" refers to "weatherproofing membrane". Would GBCI consider primer part of weatherproofing system and therefore part of building exterior, not subject to VOC or CDPH testing?