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Community and Q&A

Insulating a pole barn

Betmax77 | Posted in Energy Efficiency and Durability on

Dear Mr. Holladay,
I recently wrote to you to ask about the possibility of using rigid poly-iso with 6 mil. poly vapor membrane in my unvented 2×8 roof rafters in climate zone 6. You recommended closed cell spray foam instead. Is there any way I can improve on my original design to both solve the condensation problem and come up with a more economical solution. Since I would self-perform the rigid solution and would be installing the membrane myself would careful attention to its installation this resolve the problem with this assembly?  

Best regards,

GBA Prime

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  1. GBA Editor
    Martin Holladay | | #1

    I'm sorry that I don't remember all the details of your previous Q&A thread. (In general, it's always best to post follow-up questions on the same thread, so that everyone can read the introductory details, instead of starting a new thread.)

    If you are insulating a sloped roof assembly, here are your options:

    Option 1. If you want to insulate the roof with polyiso, the polyiso belongs on the exterior side of the roof sheathing. (Needless to say, I hope your pole barn has roof sheathing. To learn why, read this article: "Insulating a Pole Barn.") For more information on insulating a roof assembly with polyiso, see this article: "How to Install Rigid Foam On Top of Roof Sheathing."

    Option 2. As long as your roof has no valleys, hips, or dormers, you can create a vented roof assembly. Once you establish vent channels from your soffits to the ridge, the rafter bays can be insulated with a wide selection of insulation materials.

    Option 3. If your roof can't be vented, and if you can't install rigid foam on the exterior side of the roof sheathing, your only option is to insulate by installing closed-cell spray foam on the underside of the roof sheathing.

    For more information on all of these options, see "How to Build an Insulated Cathedral Ceiling."

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