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  1. #1
    Join Date
    Dec 2011

    Default Preventing Ice Dams

    This is great advice on preventing ice dams from forming. I have two questions not covered i the article:

    1. We have a turbine installed in our roof. Should this be left open and spinning in winter, provided the major warm air leaks from the house are sealed?

    2. Any special advice for metal roofs?


  2. #2
    Join Date
    Jul 2010

    Default Re: Preventing Ice Dams

    For turbine vent, there are special covers for the winter, to prevent cold air from coming in.

  3. #3
    Join Date
    Aug 2007
    Portland, Oregon, formerly of Chicago

    Default Re: Preventing Ice Dams

    Even in winter, the attic must be ventilated. Particularly if there is no other venting high on the roof through which air can exit, the turbine should stay open. If there are sufficient air vents down low in the eaves, the turbine should not create a severe negative pressure in the attic and thus suck moist, warm air from the house through voids in the ceiling.

    It is attics that are relatively cold upon which snow remains and thus does not go through the freeze-thaw cycle which creates ice dams down low by the eaves. Well ventilated attics will also not have moist air freezing on the underside of the roof decking.

    I would expect less ice daming problems on metal roofs. Metal roofs generally have steeper pitches and are ribbed or lapped to somewhat protect against water intrusion. Further, metal roofs are much slicker than other types. Often snow guards are placed on them to prevent massive snow slides from burying some poor unsuspecting person below.

    I always say that the Swiss don't build their chalets to look quaint for the tourists, but rather to protect against the heavy snows in the Alps. Steep pitches and very wide unboxed eaves with hung gutters protect the chalet. Should an ice dam form, it is outside the wall area and the hung gutters do not aid in forming a damn and do not get ripped off the chalet.

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