An ice dam is a ridge of ice that builds up along the bottom edge of a roof and stops melting snow from draining off. The water that pools behind it can work its way under the shingles and into the attic, walls and ceilings. In Naperville, Downers Grove and the rest of DuPage County, the usual cause is warm air leaking from the house into the attic, and the lasting fix is keeping that heat inside the house.
Ice dams at a glance
- What causes them: heat from the house warms the upper roof, the snow there melts, and the water refreezes when it reaches the cold roof edge.
- First warning signs: a thick ridge of ice along the gutters, long icicles, and stains on ceilings near outside walls.
- Safe first step: pull snow off the lower part of the roof from the ground with a roof rake. Stay off the roof.
- Lasting fix: seal attic air leaks, add insulation, keep soffit vents clear, and make sure the roof has ice-and-water shield at the eaves.
How an ice dam forms
Three things have to happen at once. There has to be snow on the roof. The upper part of the roof has to be above freezing. And the lower edge has to stay below freezing. The University of Minnesota Extension describes it as uneven roof temperatures, and that is exactly what a heated attic creates.
Snow on the warm part of the roof melts and runs down. When it reaches the overhang, which sits out past the heated house, it freezes again. Each round adds to the ridge. The water behind it can’t drain, so it sits on the roof and finds the gaps between shingles. From there it reaches the roof deck, the attic insulation and, sometimes, the ceiling below.
Chicago-suburb winters are made for this. A few inches of snow, a sunny afternoon near freezing, then a cold night is all it takes. The National Weather Service Chicago office issues the winter storm warnings for DuPage and Will counties, and the days after a big snow are when ice dams tend to show up.
Where the heat comes from
Most ice dams start with heat escaping into the attic. The common sources are:
- Air leaks into the attic. Warm air slips through gaps around ceiling light fixtures, the attic hatch, and holes cut for wires, pipes and ducts. In many homes this is the biggest cause.
- Thin or settled insulation. Heat moves straight through it to the roof deck.
- Bath and kitchen fans. Fans that vent into the attic, or end just above the roof, put warm, moist air right where you don’t want it.
- Ducts, chimneys and knee walls. Leaky ductwork in the attic and heat around a chimney warm the roof from below.
- Roof shape. Skylights, recessed lights and roofs with lots of valleys and dormers make ice dams more likely.
Signs you have an ice dam
You can check most of this from the ground or from inside the house:
- A thick ridge of ice along the gutters or the bottom row of shingles.
- Long icicles, especially with water dripping behind the gutter instead of off the front.
- Ice forming on the siding or windows below the eaves.
- Water stains, bubbling paint or damp spots on ceilings and upper walls near outside walls.
- Damp attic insulation or frost on the underside of the roof deck.
What to do if you have one right now
- Stay off the roof. Icy shingles and ladders against frozen gutters are dangerous. The Extension’s own warning is that anyone working on a winter roof risks injury and can damage the roof.
- Rake the snow from the ground. A long-handled roof rake takes away the snow that feeds the dam. Go gently, because the rake can scrape shingles.
- Don’t chop at the ice. Hammers, shovels and axes tear shingles and bend gutters, and the damage costs more than the ice.
- Deal with water inside fast. Catch drips, move belongings, and dry wet drywall and insulation quickly so mold doesn’t start.
- Take photos. Photograph the ice from outside and any damage inside, with dates. Our guide to ice dam damage and insurance covers what to document for a claim.
- Get the roof looked at. Once it’s safe, have a roofer check the eaves, underlayment and decking. Adept’s roof inspections are free, and if water got in, our roof leak repair team fixes the damage at the eave.
How to stop ice dams for good
Raking and melting channels only buy time. The real fix keeps the whole roof cold, so snow melts evenly or not at all.
- Seal attic air leaks first. Close the gaps around light fixtures, the hatch, plumbing stacks, wiring holes and ducts. This does the most good for the money.
- Then add insulation. Once the leaks are sealed, more insulation cuts the heat that soaks through the ceiling. In Villa Park, for example, the Village requires at least R-49 insulation when a tear-off exposes the sheathing (see our Villa Park roofing page).
- Keep soffit vents clear. Insulation pushed into the soffits blocks the airflow that keeps the roof deck cold. A roof that breathes through the soffits and out near the ridge stays closer to the outside temperature.
- Send fans outside. Bath and kitchen fans should run through ducts all the way out of the house, not into the attic.
- Make sure the roof has an ice barrier. The building code in the Chicago area calls for a self-adhering ice barrier from the roof edge to at least 24 inches inside the exterior wall. It doesn’t stop the ice from forming, but it keeps the water that backs up off the roof deck. Our asphalt shingle roofing page explains how it goes on.
If you aren’t sure where the heat is escaping, an energy auditor or weatherization contractor can run a blower door test and use an infrared camera to find the leaks.
Does the roof itself matter?
Shingles don’t cause ice dams, but the roof decides how much damage one does. An older roof without an ice barrier, or with worn underlayment at the eaves, lets backed-up water in much sooner. On every Adept roof replacement, ice-and-water shield goes along every eave and valley, built for the freeze-thaw winters in Naperville and Downers Grove. If a new roof is in your plans, ask any roofer how far up the eaves the ice barrier will run and how the attic will be vented.
Frequently asked questions
What causes ice dams on a roof?
Ice dams form when heat from the house warms the upper roof and melts the snow there. The water runs down to the cold roof edge and refreezes into a ridge that traps more water behind it. Air leaks into the attic are the most common source of that heat.
Are roofers responsible for ice damming?
Usually not. Ice dams come from heat escaping the house, not from the shingles. A roofer is responsible for installing the ice barrier the code requires at the eaves and for keeping the roof’s ventilation paths open, so a roof missing either one will leak sooner when an ice dam forms.
How do I get rid of an ice dam safely?
Stay on the ground and use a roof rake to pull snow off the lower part of the roof so the dam stops growing. Don’t climb onto an icy roof or chop at the ice, which damages shingles and gutters. If water is coming inside, call a roofer once it is safe to look at the roof.
Will a new roof stop ice dams?
A new roof won’t stop ice dams by itself, because they are caused by heat loss from the house. A new roof with ice-and-water shield at the eaves and good ventilation does keep backed-up water out of the house much better. Sealing attic air leaks and adding insulation is what stops the dams from forming.
Does homeowners insurance cover ice dam damage?
Many policies cover sudden water damage inside the home from an ice dam, but not the cost of removing the ice. Coverage depends on your policy, so check with your agent. Our guide to ice dam damage and insurance explains what to document.
Worried about ice dams this winter?
Adept Construction has served DuPage and Will County homeowners since 1997, with offices in Naperville, Downers Grove and Villa Park. If you saw ice along your gutters last winter or a ceiling stain this spring, book a free roof inspection before the snow comes. We’ll check the eaves, the underlayment and the attic venting and tell you what we find. You can also request a free roof estimate.
