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Detached insulated garage with unvented roof assembly

adepaoli | Posted in General Questions on

Hello all. I’m detailing out a detached insulated garage with an unvented roof. Curious if this would be a place to use an interior barrier like intello-plus and possibly use mineral wool insulation? Not a fan of spray foams. Asphalt shingle roof, no overhangs, monopoly framed, sitting on existing un-insulated slab, unconditioned (I think). No RCP yet, so I’m not sure how many interior penetrations the architect will be asking for, but I do know they want either collar ties or rafter ties exposed with the ceiling vaulted. I’m assuming I’ll want a service cavity inboard of the interior barrier. In this assembly, any additional reasons to use one or the other, CDX vs OSB, for both the walls and/or the roof deck? Not sure what we’ll use for WRB or roof underlayment. Thanks for any insight and advise you may have.

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  1. Expert Member
    BILL WICHERS | | #1

    Are you planning on conditioning this space? If so, will it be heated only ocassionally, or all the time? Will you heat just enough to avoid freezing, or enough to make it comfy as a workshop?

    I don't think I'd use any fancy vapor retarders. If I were to use a smart vapor retarder here, I'd use one of the cheaper ones like MemBrain. I'd use mineral wool in the walls for sure, since I like working with that product. My guess is that you'll have minimal amounts of moisture produced inside the structure, since it's unlikely to be frequently occupied, and most of the things you'd do in a garage are probably not going to make lots of moisture. I doubt you'll be boiling water in there, for example. Details depend on your plans for the use of the space though.


  2. adepaoli | | #2

    Hey Bill,

    Thanks for the response. Still figuring out exactly what the indented purpose of this space will be, but from my understanding it will be a workshop space for the homeowner, that will now have a small amount of conditioning, probably just heating. What that shop space will look like is still foreign to me, including whether anything house in the garage will introduce large amounts of moisture in the space. This garage is built within a certain side yard setback and the architect noted that bc of this certain parts of the roof can't be vented, which is why we are looking at an unvented roof assembly. For my education, would you assume this is due to some sort of potential fire danger with embers entering soffit vents if a neighboring house was to be on fire?

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