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Ice damming above cathedral ceilings

dsheinz | Posted in General Questions on

I have a 1973 home with cathedral ceiling, And I have ice daming. If I remove the shingles and plywood, seal all air leaks, install high density insulation batts, with baffles for ventilation would this solve the problem. I believe I only have 2’x8′ space in the ceiling, Wood ceiling on the inside attached to plywood.

Any suggestions?

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Replies

  1. dickrussell | | #1

    Ice damming almost always is due to heat getting to the roof deck and melting snow, by air leakage from conditioned space or insufficient insulation. Your 2x8 rafters don't leave a lot of space for any batt insulation after you take up 1.5-2" of baffle space. Further, the thermal bridging of the wood will cut severely into whatever you can fit into the space between them.

    If you are going to the expense and effort of removing the roofing anyway, think about adding a good layer of polyiso insulation over the existing roof deck, add 2x4s on the flat running vertically over that to provide a vent channel to the ridge, and finally a second nailing base with asphalt paper and roofing over that. Details can be found here or elsewhere.

  2. GBA Editor
    Martin Holladay | | #2

    Dave,
    I agree with Dick. There's not much you can do with 2x8 rafter bays, especially if the bays have vent channels.

    More information here:

    Prevent Ice Dams With Air Sealing and Insulation

    How to Build an Insulated Cathedral Ceiling

  3. Expert Member
    Dana Dorsett | | #3

    Local climate matters, and it takes more roof-R to get there in some places than others. Where are you?

    Any skylights to deal with?

    How are your walls insulated, and how much eave & rake overhang do you have?

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