Ice Dam Solutions

Solving the Problem by Paul Fisette

Check the home carefully when ice dams form. Investigate the attic, even when there doesn't appear to be a leak. Look at the underside of the roof sheathing and roof trim to make sure they haven't gotten wet. Check the insulation for dampness. And when leaks inside the home develop, be prepared. Water penetration pathways are often difficult to follow. Don't just patch the roof leak. Make sure that the roof sheathing hasn't rotted and that other less obvious problems in the ceiling or walls haven't developed. Detail a comprehensive plan to fix the damage. But more importantly, solve the problem that caused the ice dams to form.

You can try to block the flow of melt water into a house by installing a rubber membrane on the roof under the roof shingles. Or you can craft a real solution: keep the entire roof cold, and save energy dollars in the process! In most homes this means: block all air leaks leading to the attic from the house, increase the thickness of insulation on the attic floor, and install a continuous soffit and ridge vent system. Be sure the air and insulation barrier you create is continuous.

Heat loss is often worst just above the top plate, the continuous horizontal framing where exterior walls and ceilings are joined. This is partly because there isn't room in the corner for adequate insulation. Also, builders are not particularly fussy about air sealing to prevent the movement of warm air up to the underside of the roof surface. Air can leak through wire and plumbing penetrations here, or can come from wall cavities, passing between the small cracks between the top plate and the drywall.

New houses should include plenty of ceiling insulation, a continuous air barrier separating the living space from the underside of the roof, and an effective roof ventilation system. In both new and retrofitted buildings, insulation should be up to local standards. In the northern United States, this is usually at least R-38. A soffit-to-ridge ventilation system is the most effective ventilation scheme for cooling roof sheathing (see "Roofing and Siding Rehabs Get an Energy Fix," p. 25). Power vents, turbines, roof vents, and gable louvers just aren't as good. Both the baffles on the ridge vent and the sun warming up the roof help drive the air flow out of the ridge vent. Air coming in the soffit washes the underside of the roof sheathing with a continuous flow of cold air.

Insulation retards conductive heat loss, but a special effort must be made to seal warm indoor air inside. In new construction, avoid making penetrations through the ceiling whenever possible. When you can't avoid making penetrations, or when air tightening existing homes, use urethane spray foam (in a can), caulk, packed cellulose, or weatherstripping to seal all ceiling leaks.