Insulating a workshop roof
I’m in the process of rebuilding a back-yard workshop in climate zone 3, and I’m at the point where I’m considering roof insulation. I’ve read many of the articles on here by Martin and others, including:
– How to build an insulated cathedral ceiling
– Cut and cobble
I’m in a pretty similar situation to those last two threads, but do have some options. At this point, I have the exterior roof in place over attic trusses, and it’s vented with a ridge vent and soffit vents. Like that user, I’m not planning to heat this continually – just occasionally – but would still like to do the best job I can; that means I’m ok if my r-value is not as great as it could be (particularly since the top chord of the trusses are 2x4s). Ideally, I’d really prefer to not have to put a fire barrier over insulation, due to the truss construction and the difficulties of adding plywood or drywall with that. I realize, however, that that may be unavoidable. I’d like to keep the insulation up at the top chord – have the ability to store things up in the truss area with easy access.
Based on my reading, these appear to be my options:
– Baffles, plastic sheeting, blown-in insulation (vented)
– Cut and cobble with polyiso (but this seems to require a fire barrier) (vented)
– Polyiso underneath the top chord (but this now means I have two layers I have to cut around the trusswork)
– Flash and batt, ignoring my venting – does this need a fire barrier? (unvented)
– Closed-cell spray foam (unvented) – is there any that doesn’t need a fire barrier? That energyvanguard article seems to suggest that there might be some.
Other suggestions? Being honest, I principally just don’t want to have to figure out how to sheath the underside with something rigid.
Thanks so much!
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