Ice Dams – Tips for Leak Prevention / Damage Control
Design Tips To Minimize Ice Dam Leakage and Damage
There is very little that you can do to prevent ice dams from forming. You can incorporate design features when building a new home or adding on that will minimize the size of ice dams. However, some of these features may not be visually appealing when used in remodeling situations, due to the fact that the overall design of the addition may not perfectly match your existing structure.
These type of situations are perfect examples of where one would make extensive use of the specialized roofing products that were mentioned earlier. Even in new construction, the use of ice dam roofing products is a great idea. They afford you peace of mind in the event of weather conditions that favor ice dam formation.
Avoid low slope roofs whenever possible. A low slope roof generally is considered one with a pitch of 5/12 or less. Low slope roofs make it easier for water to backup underneath the roofing materials.
Extend the roof overhang as much as possible from the outside wall of your home. If possible,give strong consideration to a 2 foot minimum overhang. In the event that an ice dam forms, this large overhang may keep the ice dam away from your exterior walls. In the event a leak does develop, in most cases, the leak will come through the soffit on the outside of your home, not your interior ceilings.
Avoid changes in roof pitch on the same plane. This simply means keeping the distance between the ridge of a roof and the gutter a straight line. Don't put a 'kink' in the roof. Snow and ice collect at these points. Usually, the lower roof plane in the 'kink' is also a low slope roof as we discussed above. Avoid these if at all possible.
Consider a raised heel height at the intersection point between the roof framing and the outside bearing walls. Heel height is a common term used by rough framing carpenters. It refers to the vertical distance between the top plate of the exterior wall and the top edge of the roof rafters as they pass over the outer edge of the wall plate.
Low heel heights (4 - 6") create a tremendous problem that aids in the formation of ice dams. Not only that, these low heel heights also contribute to the leakage of water into your house once an ice dam has formed.
Good building practices dictate that you should have a 2 inch airspace between the bottom of your roof deck and any ceiling or attic insulation. If your builder or carpenter uses a low heel height, you may only have 2 to 4 inches of insulation above the ceiling where the roof passes over the outside walls of your house. This condition enables heat to escape. This heat in turn keeps the roof immediately above this location warm enough to keep the water above the ice dam from freezing.This is the water that subsequently leaks into your house. By raising the heel height of your rafters or trusses, you benefit by having more insulation at this very critical location.
In climates where snow accumulations can be excessive, consider building a 'cold roof'. This is basically a roof on top of a roof. The upper roof is separated from the lower roof by a generous ventilating space. Outside air can flow freely between the two roofs. This keeps the upper roof, the one with the snow and ice on it, cold. Believe it or not, this is exactly what you want. You want the melt water to freeze as quickly as possible in ice dam situations. This keeps the water from backing up underneath the roofing materials. Also, a cold roof design virtually eliminates the problem we just discussed concerning low heel heights.
In the United States, Canada and the Northern Hemisphere for that matter, try to orient your house with a minimum of roof area having a northern exposure. Roofs with a northern exposure, generally, have more problems, because the snow and ice melt from these at a slower rate. During the winter months, the sun is at a lower position in the sky and these roofs often do not get direct sunlight. The sun is beneficial, because it will allow the snow and ice to melt more quickly. Roof decks, gutters and downspouts in direct sunlight often will have surface temperatures above freezing, while the air temperature will be below freezing. Avoid shaded roofs for the same reason.
If building new or remodeling, give serious consideration to installing excellent continuous ventilation. This consists of full soffit or eave ventilation used in conjunction with continuous ventilation at the top of your roof.
This type of ventilation permits a constant supply of cold air to flow beneath the surface of your roof. Once again, this is a favorable condition, as it keeps the roof surface cold and can actually cause the entire surface of the roof to freeze. This in turn permits any melt water to run on top of this ice shield on its way to the ground.
Continuous ventilation also has numerous other benefits. It helps to prevent attic condensation in the winter months. In the summer it helps to lower attic temperatures.