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Community and Q&A

Insulated roof sheathing

user-6457602 | Posted in Green Building Techniques on

We have a client with a 1-1/2 story home in St Paul, MN., and they would like us to insulate their roof when it is being reroofed.  Our plan is to have closed cell foam installed from the outside but that will still only give us roughly R-21 at the 2×4 sloped ceiling areas.  Is it possible to use Huber Zip-R as a roof sheathing is we use a roofing underlayment over it?  If not, what is the best way to add insulation above the rafters?


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  1. walta100 | | #1

    I do not think the manufacture has approved ZipR for use on a roofs.

    Anyone who would put their name on a set of plans with an off label use is taking a big risk should it fail as is anyone installing off label.


  2. GBA Editor
    Brian Pontolilo | | #2

    Hi Ben.

    To get to a reasonable R-value in your area, your likely approach working from the outside is probably to fill the cavities with (there are actually many options), sheath the roof, and then install exterior rigid insulation over the sheathing. Here are two articles I would suggest you read:
    How to Build an Insulated Cathedral Ceiling
    How to Install Rigid Foam on Top of Roof Sheathing

    1. user-6457602 | | #3

      Thanks, Brian,
      Yes, we will be filling the 2x4 rafters from the outside with closed-cell foam. I was hoping there was a product like Huber Zip-R where we could install the rigid and sheathing in one step. It looks like we will probably need to do it as shown in the articles.

      1. GBA Editor
        Martin Holladay | | #4

        The product you are looking for is called nailbase. You can Google it.

  3. user-6457602 | | #5

    Perfect. Thanks for the info, Martin!

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