How to Prevent Ice Dams on Your Roof

What is an ice dam?

An ice dam is a ridge of ice that forms along the lower edge of a roof. Snow higher up the roof melts, the water runs down, then refreezes when it reaches the colder eaves. Over time the ridge grows and traps water behind it.

That trapped water can back up under shingles and leak into ceilings, walls and insulation, often without any sign until stains appear indoors.

Why ice dams form

The root cause is usually warm air escaping from the living space into the attic. That warmth heats the roof deck and melts snow from below, even on very cold days. Common culprits include:

• Gaps around attic hatches, recessed lights, plumbing vents and chimneys
• Thin or uneven attic insulation
• Poor attic ventilation that lets warm air build up under the roof
• Heating ducts running through an uninsulated attic

Seal air leaks and insulate the attic

The most effective long-term fix is keeping heat where it belongs. Sealing air leaks between the living space and the attic, then adding insulation, keeps the roof deck cold so snow melts evenly instead of refreezing at the edges.

Air sealing is detailed work and should be done before new insulation goes in, since insulation alone does not stop air movement.

Improve attic ventilation

A well-ventilated attic lets cold outside air flow in at the eaves and out near the ridge. This keeps the underside of the roof close to the outside temperature. Soffit vents need to stay clear of insulation, and ridge or roof vents need to be sized for the attic.

Add protection when you re-roof

If your roof is due for replacement, it is the ideal moment to add a self-adhering ice and water barrier along the eaves and in valleys. This membrane helps protect the roof deck if water does back up. Many building codes in snowy regions require it.

What to do during winter

• Use a roof rake from the ground to pull snow off the lower edge of the roof after heavy storms.
• Keep gutters and downspouts clear before winter arrives.
• Never climb onto an icy roof or chip at ice with sharp tools, which can damage shingles and cause serious falls.
• If water is coming inside, contact a professional promptly.

Our roofing upgrade service looks at the roof, attic insulation and ventilation together, so the fix lasts.