Preventing Ice Dams on Homes
When heat from the interior of a house with a sloped roof escapes into the attic space, it warms the underside of the roof. Meanwhile, the roof eave outside the heated space remains a colder temperature.
As snow accumulates on the rooftop, it melts over the warmer portion of the attic and the melt water runs down the roof. When it encounters the cold edge of the roof it refreezes. The refrozen water along the roof edge creates an “ice dam” and consequently, the melted snow running down the roof begins to back up underneath the roof covering. This water will soak the roof sheathing and leak into the attic unless there is a barrier above the sheathing. Sealing the roof deck is an effective way to prevent the water from entering your home and causing damage.
Preventing ice dams
When re-roofing:
Installing a new roof is the perfect time to seal the roof deck by installing a moisture barrier on top of the decking, before installing the roof covering. This affordable option will help keep water out of your home due to moisture from ice dams, as well as protecting the house from wind-driven rain if the roof cover blows off during a windstorm. The moisture barrier should extend from the edge of the eaves to at least 24 inches beyond the inside of the exterior wall.
Here are some options for sealing the roof deck:
- Install a “peel and stick” membrane over the entire roof deck;
- Install 4″-6″ wide “peel and stick” tape installed over all the wood roof panel seams, covered by a 30# felt underlayment over the entire roof;
- Install a high tear strength synthetic underlayment with all vertical and horizontal seams taped;
- Install a closed cell polyurethane spray foam applied to the underside of the roof sheathing at the joints between the sheathing panels and along all intersections between roof sheathing and all roof framing members.
Things you can do before re-roofing:
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To help prevent ice damming, remove or relocate heat sources that are installed in open attic areas directly under the roof, such as an attic.
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Light fixtures in the ceiling below an unheated attic space and particularly those in cathedral ceilings the open area that is directly under your roof, such as attic space or a mechanical room, should be insulated.
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Recessed light fixtures release heat if they are not insulated.
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Check to see if there is any visible light from these fixtures in the attic.
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If there is, they probably are not adequately sealed or insulated. Seal or insulate those light fixtures immediately.
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If you have penetrations into the attic, such as vents, seal and insulate them so that daylight cannot be seen and airflow is minimal.
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Insulate, seal, weatherstrip or gasket all attic access doors.
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Attic penetrations and access doors, which are not properly sealed and insulated, allow for heated air to escape into the attic and can contribute to an ice damming condition.
Removing ice dams
IBHS does not recommend chipping or breaking ice dams due to the damage that can be inflicted on the roof. If you are not physically capable of going onto the roof or are unable to easily reach the roof, consult a roofing professional.
For low slope roofs or flat roofs:
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Removing the snow will remove the source of a potential ice dam.
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Use a heavy duty push broom with stiff bristles to brush off the snow on low slope or flat roofs.
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A shovel or snow blower should not be used since they may tear up the roof cover system.
For steep slope roofs:
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Removing the snow will remove the source of a potential ice dam.
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A roof rake may be used for most single story buildings while remaining on the ground to pull snow down the roof slope.
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Do not pull snow back against the slope or sideways since the snow may get underneath the cover and can break shingles.
Another great resource article by The Insurance Institute for Business & Home Safety.
http://www.disastersafety.org/freezing_weather/preventing-ice-dams-on-homes/
