How to Cure Ice Dams

Ice dams create pooled water on the roof, causing leaks and damage.

Ice dams are created when warm air in your home's attic space heats the roof deck enough to melt snow on top of the roof. As the water flows down toward the eave, where the roof deck gets colder, it freezes, eventually creating a dam of ice. The dam causes water to pool along the eave, where it can work its way under the roofing and down into the house. The key to preventing ice dams is keeping the roof deck as cold as possible. You do this by air-sealing and improving insulation in the attic floor -- to keep heated air inside your living space -- and by improving ventilation under the roof deck.

Things You'll Need

• Silicone caulk
• Expanding spray foam
• Foam weatherstripping
• High-temperature silicone caulk
• Aluminum sheeting
• Tin snips
• Insulation
• Insulation baffles

Instructions

Air-Seal the Attic Floor

1. Inspect your attic floor thoroughly for potential air leaks, pulling back insulation as needed. Common areas for leakage include electrical boxes for ceiling light fixtures and fans, recessed (can) light fixtures, plumbing vent pipes, exhaust flues (metal ducts) for the water heater and furnace, fireplace chimneys, attic access doors, and recesses for ceiling soffits.

2. Seal air leaks with silicone caulk and expanding spray foam. Use caulk for sealing small gaps up to about 1/4 inch wide, and use spray foam for larger gaps up to about 3 inches wide. Do not use standard sealants around chimneys or appliance exhaust flues. Seal access door openings with self-adhesive foam weatherstripping.

3. Seal gaps along fireplace chimneys and exhaust flues with high-temperature silicone caulk. Cover large gaps around exhaust flues by cutting pieces of sheet aluminum to fit snugly around the flue pipe, using tin snips. Secure the sheets to the backside of the ceiling surface with high-temperature caulk, then caulk the joint between the sheets and flue pipe.

Improve Your Home's insulation

1. 

   Adequate insulation is key in preventing ice dams.

   Consult your city's building department or a certified energy auditor or other qualified building professional to learn about the recommended levels of insulation (R-value) for attic floors in your geographical area. If necessary, add insulation to the attic floor to meet or exceed recommended levels.

2. Insulate the floor area behind attic knee walls, if you have them. Builders and remodelers often insulate inside knee walls, but fail to insulate the attic floor behind knee walls.

3. Check for insulation within ceiling soffits and other framed recesses in the attic. Soffits are often used to house light fixtures in the rooms immediately below attics. Insulate these areas as appropriate, using rigid-foam insulation or insulation blankets.

4. Consider replacing older conventional recessed light fixtures with new fixtures rated "ICAT" (Insulated Ceiling Airtight). These fixtures have sealed housings and can be covered with insulation. Conventional recessed fixtures (if not rated "IC," for insulated ceiling) cannot be covered and require a 3-inch air space on all sides, resulting in air leakage and loss of heat from the home.

Ensure Proper Attic Ventilation

1. 

   Proper attic ventilation is a must year-round.

   Inspect the attic to assess the levels of ventilation provided by soffit vents (for air intake), roof or ridge vents (for air exhaust), or gable-wall vents (for both intake and exhaust). Make sure all vents are clear so that air can freely flow into and out of the attic space.

2. Install insulation baffles, if necessary, to prevent attic floor insulation from blocking airflow from soffit (eave) vents. Baffles are available at home improvement stores and are easy to install following the manufacturer's directions.

3. Consider improving attic ventilation by adding vents or replacing existing vents with continuous strip vents in soffits and a continuous ridge vent along the peak of the roof (both are jobs for warm weather). Consult with an independent building professional, such as a home energy auditor, to discuss options and recommendations before contacting a roofing contractor to have vents installed.

Tips & Warnings

• Air-sealing and insulation are the most important and effective steps for preventing ice dams in most homes; focus on these remedies first.

• When it's time to replace your roofing, install a waterproofing underlayment (ice and snow membrane) along the eaves to provide additional protection against water damage from ice dams. This won't prevent ice dams from forming, but it can help keep water out of your house if dams do develop.

References

• Fine Homebuilding: Preventing Ice Dams; Martin Holladay
• University of Minnesota Extension: Ice Dams
• Energy Star: A Do-It-Yourself Guide to Sealing and Insulating with Energy Star