You've probably seen them, even if you didn't know the name. Thick ridges of ice along the edge of a roof, with icicles hanging off the gutters. They look like winter. But behind that ice, water can be backing up under the shingles and into the house. Here's what's actually happening, and how to stop it.
It starts in the attic
An ice dam isn't really a roof problem at first. It's an attic problem. Heat from your living space leaks up into the attic through gaps in the insulation, around light fixtures, attic hatches and pipes. If the attic can't vent that warm air out, it warms the underside of the roof.
The snow melts, then refreezes at the edge
Snow sitting on that warm roof melts from underneath, even when it's well below freezing outside. The water trickles down the roof until it reaches the edge, the eaves, which hang out past the warm part of the house and stay cold. There, it freezes again. Day after day, layer by layer, the ice builds into a dam.
That water backs up under your shingles
Shingles are made to shed water running down the roof, not to hold back a pool of it. With the dam in place, new meltwater has nowhere to go. It backs up behind the ice and works its way up and under the shingles. From there it can soak the roof deck, drip into the attic, and show up as stains on ceilings and walls, sometimes far from the edge of the roof.
The fix: good attic ventilation and insulation
The real cure is keeping the roof cold. Good insulation keeps your home's heat in the house instead of the attic. Good ventilation, with air coming in low at the soffits and out high at the ridge, carries away any warmth that does get up there. When the whole roof stays about the same temperature as the outside air, snow doesn't melt unevenly, and the cycle that builds ice dams never gets started.
Plus ice and water barrier at the eaves
Ice and water barrier is a self-sealing membrane installed under the shingles along the eaves, where ice dams form. If water does back up, the barrier helps keep it from reaching the wood and getting into the house. It's a backup layer of protection, and on a new roof it should be part of the job.
What not to do
Don't climb on an icy roof, and don't chip at the ice with a hammer or shovel. You can damage shingles and gutters and get hurt. If water is coming in, put down towels and buckets, take photos, and call.
Get to the root of it
Our free inspection includes the attic, so we can see why your roof is building ice and tell you straight what will fix it. If it's leaking now, call any time. We answer 24/7.
What John says in the video
Transcript: What causes ice dams on your roof? Here's the deal. Heat leaks out of your attic, melts the snow, and it refreezes at the edge of your roof. That water backs up under your shingles. The fix? Good attic ventilation and insulation, plus ice and water barrier at the eaves. Call me, 1-800-JOHN-BEAL.
Frequently asked questions
What is an ice dam?
A ridge of ice that forms along the edge of a roof. It traps melting snow behind it, and that water can back up under the shingles and leak into the house.
Why do ice dams form?
Heat escaping from the attic warms the roof and melts snow from underneath. The water runs down to the colder roof edge and refreezes, building the dam.
How do you prevent ice dams?
Keep the attic cold with good insulation and ventilation so heat does not reach the roof, and have ice and water barrier installed along the eaves to protect against water that backs up.
What is ice and water barrier?
A self-sealing membrane installed under the shingles along the eaves and other vulnerable areas. It helps keep water out if it backs up under the shingles.
Can John Beal Roofing help with ice dams?
Yes. We check attic ventilation as part of our free inspection, and install ice and water barrier on our roofs. Call 1-800-JOHN-BEAL, answered 24/7.
More answers from John Beal
- Roof Leaking During A Storm? What To Do
- How Much Does A New Roof Cost?
- Can I Replace Just Part Of My Roof?
- All of John’s video answers
John Beal Roofing is family-run and has been roofing Midwest homes since 1947, serving Greater St. Louis, Kansas City, Columbia, Springfield, Lake of the Ozarks, and the Metro East and Carbondale in Illinois. Our Kansas City office is at 7440 NW River Park Drive, Parkville, MO 64152 (816-572-9500 Missouri side, 913-281-6000 Kansas side). Everywhere else, call 1-800-JOHN-BEAL. We answer 24/7.