What Causes Ice Dams on Chicago-Area Roofs, and How Do You Stop Them for Good?
By Sam Pipiras, Director of Commercial Development · Published October 2026 · 6 min read
You see icicles along the eaves and a brown stain on an exterior wall or ceiling, and the first thought is gutters. It almost never is. Ice dams are a heat problem inside the house, and winter is close, which makes this the right time to deal with the cause instead of the symptom.
Quick Answer
An ice dam forms when heat escaping from your living space warms the roof deck, melts the snow above it, and the meltwater refreezes at the cold eaves. The ice then blocks the path of more meltwater, which backs up under the shingles. The permanent fix is air sealing, attic insulation and balanced ventilation, with an ice barrier membrane at the eaves as a backup. Shoveling and heat cable treat the symptom only.
What Actually Causes an Ice Dam?
Snow on a roof melts from the bottom up when the roof deck is warm. That warmth comes from the house: gaps around attic hatches, recessed lights, bath fan ducts and wall top plates let heated air leak into the attic, and thin insulation lets heat conduct straight through. The upper part of the roof warms, snow melts, and the water runs down to the eave, which stays cold because it hangs past the exterior wall.
At the eave the water freezes. The ridge of ice grows, and the next round of meltwater pools behind it. Shingles are built to shed water downhill, not to hold a pool, so that water works up under the laps and into the decking, the insulation and eventually your ceiling.
Are Clogged Gutters the Real Problem?
Not usually. Full gutters can make an ice dam bigger, and cleaning them in the fall is still worth doing. But a roof with clean gutters and a warm attic will still build ice at the eave. If the attic were as cold as the outdoors, the snow would melt slowly from the sun or not at all, and no dam would form. That is why two houses on the same street, with the same gutters, can have completely different winters.
Why Heat Cable and Roof Raking Are Not a Cure
Heat cable melts a channel through the ice so water has a path off the roof. It can help a trouble spot get through a bad week, but it runs on electricity, it fails at the worst moments, and it leaves the heat loss in place. Raking snow off the lower few feet of the roof reduces the load, but it is cold, awkward work and it is easy to damage shingles with the wrong tool. Neither one changes why the roof is warm.
How Do You Stop Ice Dams for Good?
The permanent fix works in this order:
- Air seal the attic floor. Close the gaps around hatches, light fixtures, plumbing and wiring penetrations, and duct chases. Stopping air movement matters more than adding insulation on top of leaks.
- Add insulation to the recommended level for our climate. A well-insulated attic floor keeps house heat out of the roof space. Your insulation contractor or energy auditor can confirm the right depth for your house.
- Balance the ventilation. Cold air should enter at the soffits and leave at the ridge, so the underside of the deck stays near outdoor temperature. Blocked soffit vents and insulation stuffed into the eaves are common culprits.
- Route exhaust fans outdoors. A bath fan that dumps into the attic adds heat and moisture right under the deck.
Some of that is insulation and air sealing work that sits outside a roofer's scope. We will tell you what we see from the attic and the roof, and you can bring in the right trade for the rest. The roofing side of the job is the ventilation path, the condition of the decking, and the membrane at the eaves.
Does an Ice Barrier at the Eaves Help?
Yes, as protection, not as a cure. A self-adhering ice and water membrane installed over the deck at the eaves, under the shingles, seals around nails and blocks water that does get pushed up the roof. If your roof is coming off anyway, adding the membrane at the eaves and in valleys is one of the better upgrades you can make. It does not replace fixing the heat loss, because a dam can still damage gutters, fascia and soffits.
What Should Mokena-Area Homeowners Do Before the First Hard Freeze?
In Mokena and the surrounding southwest suburbs, the freeze-thaw swings between a cold night and a sunny afternoon are what build ice at the eaves. Many Mokena homes are 1990s and 2000s subdivision builds, and attic insulation and air sealing from that era often fall short of what is recommended today, so it is worth checking yours. Before winter:
- Walk the attic with a flashlight and look for dark staining on the underside of the deck, compressed insulation, or daylight around penetrations.
- Confirm soffit vents are open and not buried in insulation.
- Clean the gutters and check that downspouts discharge away from the house.
- Have the roof looked at if you have had a stain in the same spot before. A documented inspection with photos tells you whether the issue is the roof or the attic.
If you already have a stain, it is worth a visit before the weather turns. See our roof repair page for how we approach leaks, or read about full replacement if the roof is near the end of its life. We cover Mokena and the towns around it.
Frequently Asked Questions
They can. Water backed up behind the ice can get under the shingles and wet the decking, insulation and ceiling below. The weight of ice can also pull on gutters and strain fascia. Repeated cycles add up over several winters.
Not by itself. A new roof helps if it adds an ice barrier at the eaves and corrects ventilation, but the heat loss from the house is the cause. Without air sealing and insulation, a new roof can still build ice at the eave.
No. Heat cable can create a drainage channel in the ice and reduce damage during a bad stretch, but it uses electricity, can fail, and leaves the real cause in place. Think of it as a short-term aid, not a cure.
Yes. Ventilation keeps the underside of the roof deck near outdoor temperature so snow melts evenly instead of in patches. Air should enter at the soffits and exit at the ridge, with no insulation blocking the path.
Be careful. Roof rakes from the ground are safer than climbing up, and the wrong tool can scrape off granules or break shingles. Never work on an icy roof. If ice is already causing a leak, call a contractor for an inspection.