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Community and Q&A

Insulating a cathedral ceiling

Sgagne199 | Posted in Green Building Techniques on

I am building a cape style new house and I am trying to find a good cost effective green way to insulate the cathedral ceiling that is in half the house. I was thinking about putting roxul in between the rafters and foil faced foam over the rafters in full sheets and taping the seams to stop thermal bridging. I am in climate zone 6. Looking for any suggestions thanks

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  1. GBA Editor
    Martin Holladay | | #1

    If you are building a new house, you have an excellent opportunity to get things right. Most Capes are a nightmare to insulate, because the builders never installed rigid foam on the exterior side of the roof sheathing.

    The key to making this work is exterior rigid foam. I can't emphasize this fact enough. All other approaches, including the one you suggest, are inferior.

    There are three main approaches to installing rigid foam on your roof:

    1. You can install one or more layers of rigid foam above the roof sheathing, followed by a second layer of roof sheathing. (This is the best approach, because it allows you to install multiple layers of rigid foam with staggered seams.)

    2. You can install nailbase.

    3. You can install SIPs.

    Here is a link to an article to help you: How to Install Rigid Foam On Top of Roof Sheathing.

  2. Sgagne199 | | #2

    I would definetly take your advice on that but my roof is already shingled. What would be my best option knowing that I am limited to interior insulation now?

  3. GBA Editor
    Martin Holladay | | #3

    Here is a link to an article that explains all of the different ways to insulate a sloped roof assembly: How to Build an Insulated Cathedral Ceiling.

    You may also want to read this article -- it will help you avoid pitfalls when insulating the triangular attics behind your kneewalls: “Two Ways to Insulate Attic Kneewalls.”

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