Cold roofs prevent ice damming and structural damage caused by moisture seeping through the roof. Traditional cold roofs have a well-ventilated attic, while unventilated cold roofs use a breathable polypropylene membrane. Both reduce winter humidity and keep the building cool in warmer weather.
With a cold roof, the roof temperature stays the same as the outside air temperature. The cold roof prevents ice damming, which can be a normal hazard with warm roofs. Ice dams form when snow melts on the roof and then refreezes on the roof overhang. As the snow melts, water is captured by the ice dams, causing moisture to seep through the roof into the building, which can cause structural damage. With cold roofs, since the snow does not melt, there is no question of ice damming and all the problems that come with it.
The traditional cold roof construction consists of a well-ventilated attic with a pitched roof. The insulation is placed horizontally between the attic joists and the underlying floor ceiling. Any gaps in the ceiling are sealed to keep moist air out of the building. The roof beams have a bituminous substrate which cannot be penetrated by air and moisture.
The space between the sloping beams and the insulation is ventilated. Warm indoor air rises and escapes through the vents, and the interior space fills with cold outdoor air. The temperature between the outside and the inside stabilizes soon. There is some risk of condensation in these types of cold roofs.
There is also a cold roof design with an unventilated attic space. Here, the cold roof insulation is placed in the same way as for the ventilated cold roof, and the ceiling is completely sealed to prevent moist air from entering the attic. A breathable polypropylene membrane is used as the underlay; this allows indoor humid air to diffuse through it, but prevents outdoor moisture from entering the interior. There are no vents and any moisture in the space exits through the vent membrane.
The risk of condensation is low with unventilated cold roofs. If there are water pipes running through the space, however, there may be a chance that they will freeze. This problem can be solved by covering the pipes with insulation.
In addition to preventing ice damming, cold capping is helpful in keeping the building’s ceiling insulation in proper condition. By ventilating the attic well and eliminating internal humidity, a cold roof reduces winter humidity inside the building. As the weather gets warmer, a cool roof comes in handy by keeping the building cool.
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