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Community and Q&A

Unvented cathedral eave/soffit insulation?

brentwilson | Posted in General Questions on

Is it correct that roof overhangs should be insulated due to the potential for warm air (heated by solar energy on the wall of the house) to rise up and cause ice dams on an uninsulated roof overhang?

Based on the attached diagrams, I am wondering about the regular 2′ overhangs, as well as about the boxed-in void areas above the 6′ covered walkways on some sides of the house.

Climate Zone: 6B

Unvented cathedral ceiling/roof assembly

What advice do you have for me on this?

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  1. Expert Member
    Malcolm Taylor | | #1


    Living in a mild climate I don't know much about ice-dams, but looking at your section I have two small suggestions.

    - You might consider using rim-joist material for blocking, rather than making them from I-joists.

    - Those walls are crying out for some exterior insulation.

    1. brentwilson | | #2

      Yeah, the rim joist material makes sense.

      And yes, the walls on that drawing are low on insulation. I may end up using Zip R on the walls.

  2. GBA Editor
    Brian Pontolilo | | #3

    Hi Brent.

    I have heard that ice dams can form from the causes you describe. I think Dana described in pretty well in response to a question not long ago. If you want to do some searching, you may find it. But since none of the high performance homes that I have looked at over the years have insulation that extends beyond the top plate (unless it is above the roof deck, which is more a matter of build-ability than efficiency), I don't think it is too much of a concern.

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