Now that we are in the heart of winter in a good portion of the world, we thought it would be a good time to talk about extreme ice in the roof gutters, which can result in water leaking on the wall inside the house.
These ice dams in the gutters are the result of warm attic air heating the inside of the roof. This then causes snow at the snow-shingle interface to melt, and the melted snow to run down as water under the rest of the snow on the roof. When the water reaches the edges of the roof, it tends to freeze again because the edges are not under warm living areas. So then a dam is formed that causes additional melted snow to pool. When you have a pitched roof, it is designed to shed water, not to protect against standing pooled water. So as the melted snow accumulates and pools, it backs up under the shingles and leaks into the house. If this has ever happened to you, you know what kind of damage it can cause to the inside of your home. Water damage is no fun!
In terms of what to try to do to prevent these ice dams, the best method is to try to keep your whole roof cool, that's to say keeping the heat in the attic from heating the inside of the roof. The way to do this is to heavily insulate the attic floor and to ventilate the attic extremely well. Ventilation can be increased by installing continuous soffit and ridge vents. When insulating make sure that you cover the top plate of the exterior stud walls. Also, make sure insulation does not block the airflow from the soffit vents to the ridge vents. Installing baffles over the insulation can take care of this.
Besides the above mentioned steps, you should also prevent heat from living spaces from getting into the attic. The biggest culprit here is usually the attic stairway. One way to deal with this potential airway of warm air is to make a rigid hood from polystyrene-foam board insulation and use it to cover the stairway hatch.
We hope this may answer some questions about ice-dam problems!