How to Prevent Roof Ice Dams

Roof Ventilation and Attic Insulation are vital for Preventing Roof Ice Dams

By Mark J. Donovan




Every winter there are many homeowners throughout the colder climate regions of the country who experience the damaging effects of roof ice dams. Roof ice dams can cause superficial and structural damage to a home. Moreover they can cause major water damage inside the home. Fortunately roof ice dams can be prevented with proper attic insulation and roof ventilation. So before the cold weather and snow hits this winter inspect your roof and attic this fall.

First take a look at your roof. When inspecting it, make sure there is a ridge vent and that it is by no means blocked up from venting attic air out through it.

The ridge vent should run nearly the entire length of the roof peak. Then take a look at the soffit vents. Make sure you have some, and that they too are not clogged up.

The soffit and ridge vents ensure cool outside air is drawn into the attic via the soffit vents and then vented out through the ridge vent. This flow of cold air pulls any small amount of warm moist air that may have worked its way up from the finished lower levels of the house and into the attic.

Next take a look in your attic. Make sure that your attic has the proper amount of insulation in it for your climate region. Pay particular attention to the attic floor. If there is inadequate insulation in it, warm moist air will work its way up into the attic during the cold winter months. When it does, it will heat up the roof sheathing and cause the snow that is in contact with the shingled roof to melt.

When the snow begins to melt from its underside it drips down the roof shingles until it refreezes near the colder roof eaves. As the water refreezes the ice dams grow in size. Eventually enough melting snow water will work its way up behind the shingles, and when it does that’s where the real disasters begin to happen.

How to prevent ice dams this winter.

The melted snow water drips into the attic, and then onto the drywall ceilings. If left unchecked, the water will continue to work its way downward through the house.

The main goal in preventing roof ice dams is to ensure that as little warm moist air as possible works its way up into the attic, and any that does gets quickly drawn out of the attic. Ultimately the main objective is to ensure the attic is close to the outside ambient air temperature as possible. Doing so will prevent the possibility of causing the roof snow from melting from its bottom side.

To know how much attic insulation your home requires visit the Department of Energy’s website. It lists recommend insulation R-values for each area of a home for the various climate regions around the country. Also keep in mind that it is important that the requisite amount of attic insulation be installed properly. If installed improperly, such that there are open paths from the heated lower levels of the home to the attic, then significant attic heating will occur. Not only will this situation lead to ice dams, it will also cause you to have higher monthly heating bills. Consequently, when installing attic insulation, make sure there are no air gaps between ceiling joists bays. Moreover pay particular attention in preventing air gaps around chimneys and vent stacks.

Also check the attic insulation around the soffit vent areas. Make sure the attic insulation is in no way clogging them and preventing the flow of outside air into the attic.

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Another important item to check in the attic is the bathroom exhaust vents. Make sure they are vented not just into the attic, but instead out of the home via ductwork. The last thing you want to do is blow warm moist air from the bathroom up into the attic. It’s a killer for creating roof ice dams.

If you still have concerns after addressing the attic insulation and roof venting items, consider installing ice dam heating cables along your home’s roof eaves. They are inexpensive and easy to install. Roof heat cables are much better for your asphalt roof shingles then raking snow off your roof after every snowstorm. Not only can snow roof rakes be tough on your asphalt shingles, it is a time consuming chore to have to do after every snowstorm.

After performing all of these tasks and making corrective actions where necessary you should find that your home is ice dam free this coming winter.


For more help on Shingling Your Home’s Roof, see HomeAdditionPlus.com’s Asphalt Shingle Roofing Bid Sheet. The Asphalt Shingle Roofing Bid Sheet will help to ensure that your roof won’t end up with a blue tarp over it and a dumpster sitting in your yard for weeks as you wait for the roofing contractor to come back and finish roofing your home.

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