Difference Between Hot & Cold Roof Insulation

Ice Dams

• One of the most significant problems that can result from temperature differences on a roof is the creation of ice dams. These obstructions occur when warmer conditions on the top of the roof result in snow turning to water and running down the shingles. Freezing temperatures at the lower portion of the roof turn the water to ice, which creates a dam that backs up any water behind it. The blocked water can result in serious damage to the roof, ceiling and walls.

Water Vapor

• Another problem from air rising through the home, particularly when the humidity in the home remains high, results from water vapor condensation. Water vapor, which is the water in a nonliquid form, can rise through the home and condense, or turn back into a liquid, when it reaches the cooler temperatures of the attic. Moisture that contacts the roof decking can lead to damage such as wood rot.

Cold Roof

• The most prevalent method of dealing with problems caused by hot air or water vapor is keep the attic cold, so that hot air does not warm the roof exterior and does not collect near the sheathing. Called a cold roof system, this type of design incorporates vents at the soffits and near the roof peak. The system allows hot air to quickly exit though the roof top without warming up the roof exterior. Fiberglass insulation blankets or blown cellulose insulation is typically used in the cold roof system. The insulation traps much of the hot air that rises from the home, while the vents remove the rest.

Hot Air

• The hot roof system uses a different type of insulation to preventing warm air or water vapor creating any damage. Hot roof systems do not rely on venting to move air through the roof. This type of design uses a spray foam insulation that creates such a tight seal that no warm air or moisture can get through. As a result, no snow on the roof melts to cause ice dams and the sheathing avoids any damage from condensation.