Ice Dams on Spokane Roofs: Why They Form and What to Do

Updated November 12, 2026 · 6 min read

How an ice dam actually forms

Three ingredients have to line up: snow on the roof, heat escaping from below, and cold air outside.

Warm air from the living space rises into the attic. Where the attic floor is thin on insulation or full of gaps, that warmth heats the roof deck. The snow lying on the upper part of the roof melts and runs down. At the eave, which hangs past the heated walls, the roof is as cold as the outdoors, so the water freezes again. Over days of this, the frozen edge grows into a thick ridge.

Once the ridge is there, new meltwater has nowhere to go. It pools behind the ice. Shingles are designed to shed water downhill, not to hold it back, so water seeps up under them, through the underlayment and into the roof deck.

Why Spokane roofs are set up for it

Spokane winters often swing above and below freezing within a few days. A sunny afternoon can melt the snow on a south-facing slope, and the next night drops it back into the teens. That freeze-thaw cycle drives the melt, refreeze and build-up pattern.

In years with heavy snow, a deep blanket also works as extra insulation, which keeps the heat from your attic from escaping through the snow and makes the melting uneven. Rain-on-snow events add to it by dumping water onto an existing snow load.

Houses differ in how likely they are to dam up:

• Older homes in neighborhoods like South Hill and Browne's Addition often have thin attic insulation, leaky ceiling plaster, and chimneys and plumbing stacks that carry heat upward.
• Homes with complicated rooflines, including dormers, valleys and additions, collect snow where roof planes meet.
• Homes on open, windswept ground, such as parts of Five Mile Prairie, can see snow drift against upper walls and pile unevenly on roof planes.
• Houses with covered or poorly ventilated attics trap warm, moist air that rises from kitchens and bathrooms.

What causes the heat loss

Look for the leaks in the attic floor first. The common culprits are:

• Insulation that is thin, compressed, or missing around the edges.
• Gaps around recessed light fixtures, attic hatches and pull-down stairs.
• Bathroom and kitchen fans that vent into the attic rather than outside.
• Open gaps around chimneys, plumbing vent pipes and wire penetrations.
• Heating ducts running through the attic with leaks or little insulation.
• Soffit vents blocked by insulation, which stops cold air from flowing under the roof deck.

A well-ventilated attic stays close to the outdoor temperature, so the roof surface stays cold and snow does not melt unevenly. Ventilation and air sealing do the work together. Insulation alone, with open gaps, does very little.

Signs of a leak inside the house

Ice dam water usually enters near the exterior walls, so the first damage is often on the upper edge of a wall or along the ceiling at the perimeter.

• Water stains or brownish rings on the ceiling near an exterior wall.
• Paint that bubbles, peels or turns soft.
• Drips from a light fixture, a fan or a ceiling vent during a thaw.
• Wet or matted insulation when you look into the attic.
• Dark streaks on the inside of a wall near a window.
• Damp drywall at the top of an exterior wall, a musty smell, or small spots that return after painting.

If you see water, put a bucket under it, move belongings out of the way and photograph it. If a ceiling is bulging with trapped water, keep everyone out from under it, because a bulge can bring down a whole section of drywall.

Safe steps to take right now

1. Stay off the roof and off the ladder. An icy surface, snow and a ladder on frozen ground are a risky mix. Do not chip, pound or hack at the ice.
2. Rake the snow from the ground. A long-handled roof rake with wheels, used from the ground, can pull the first few feet of snow off the lower roof. Do not scrape down to the shingles, and be careful of falling snow and ice.
3. Cool the attic if you can. Keep the attic hatch shut, pull back on bathroom steam, and let the attic stay cold. Do not run extra heat into the ceiling below.
4. Open a channel only if it is safe. Roofers and some restoration companies use low-pressure steam to cut channels through ice, which is slower and gentler than chipping. This is not a job for a home hose.
5. Protect the inside. Move furniture, roll up rugs, switch off any lights on a wet ceiling circuit, and keep people out from under bulging drywall.
6. Document and call. Photograph stains, wet insulation and the roof edge from the ground, then call a roofer for the cause and a restoration crew for the water.

Water damage in ceilings and walls

A roof leak behaves differently from a pipe leak. The water travels along rafters and the top plate, soaks into insulation and shows up a few feet from where it entered. By the time a stain appears, the attic insulation and the drywall backing may have been wet for days.

Three things then happen. Insulation gets heavy and loses its value as insulation, which makes the heat loss worse. Drywall softens and may sag. And the damp, dark space above a ceiling, with organic material and little air, is an easy place for mold. Our roof leak water damage page explains how the crew finds and dries the wet layers, and the mold remediation page covers what happens if growth has already started.

Drying a ceiling takes more than a fan. The crew uses a moisture meter and sometimes a thermal camera to trace where the water went, removes wet insulation and drywall that cannot be saved, and sets air movers and dehumidifiers. If you want to know what a finished ceiling job involves and what shapes the bill, the ceiling water damage repair cost guide breaks down the factors.

Preventing the next one

Fix the cause, not the ice.

• Air seal first. Close gaps around light fixtures, hatches, wiring and plumbing stacks.
• Add insulation to the attic floor until it is deep and even, including right out to the edges.
• Check ventilation. Soffit vents should be clear, with baffles that keep insulation from blocking the airflow, and ridge or gable vents should let air out.
• Vent fans outside. Bath and kitchen fans should discharge through the roof or wall, not into the attic.
• Insulate and seal ducts that run through unconditioned space.
• Clear gutters in fall so meltwater has somewhere to go.
• Ask a roofer about ice and water shield, a sticky waterproof membrane that goes under the shingles at the eaves during a re-roof. It does not stop dams, but it protects the roof deck if one forms.

Do the attic work in the fall, before the first deep snow, when it is easier to work and the weather helps.

Insurance and costs

Insurers often separate the roof repair, the interior water damage and the ongoing cost of insulation and ventilation upgrades. Each is handled differently, and upgrades are normally your own expense. What the interior cleanup costs depends on how much ceiling and wall is wet, whether insulation has to come out, how long the water sat, and whether mold is present. The inspecting company gives you a written figure before work starts.

Sources and official resources

• Verify a Washington contractor (Washington L&I)
• Home insurance guide (Washington Insurance Commissioner)
• IICRC: restoration industry standards body
• Spokane weather and freeze warnings (National Weather Service)
• A Brief Guide to Mold, Moisture and Your Home (EPA)