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Community and Q&A

Roof snow system

Patricia ONeil | Posted in General Questions on

I built my home with a non vented attic & soffits. We used a combination of open and thermal closed cell insulation to meet code requirements. I also installed a Heat exchange Air Exchanger to regulate the air/moisture in our home.. I live in Colorado at 9,200 feet. Ice dams are formed when the snow melts from heat reaching the roof and then freezes when it hits the unheated eaves. Will this happen with the metal non vented roof system I put in? I am leaning towards installing snow bars and putting heat tape in the gutters and downspouts. I need help deciding what snow/ice systems would be best for me.

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  1. GBA Editor
    Martin Holladay | | #1

    It's unclear from your paragraph whether your house has already experienced ice dams, or whether you are just worried about that possibility.

    If your house is already built, and you have not yet had any ice dams, my advice is not to worry until you have a problem.

    If your house isn't finished yet, or if you have already gone through a winter and have experienced ice dams, there are things you can do.

    In general, the best way to design a roof to prevent ice dams is:

    1. To make sure that the roof assembly is as airtight as you can make it.

    2. To provide plenty of R-value to your roof assembly -- either meeting or exceeding minimum code requirements (probably R-49 in your climate zone).

    3. To make sure there is minimal thermal bridging through your rafters. (This may be a problem in your case, especially if all of your insulation has been installed between your rafters. The usual remedy is to install one or more layers of rigid foam above the roof sheathing.)

    4. To install ventilation channels from soffit to ridge above the upper layer of rigid foam.

    Not all of these measures are strictly necessary, but that's the best way to build a roof if you are worried about ice dams.

    Your suggested measures -- especially the use of heat tapes -- are not recommended by green builders.

    For more information, see these two articles:

    Prevent Ice Dams With Air Sealing and Insulation

    Ice Dam Basics

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