In This Guide
Ice dam water intrusion is one of winter's sneakiest home disasters. It does not come from a burst pipe or a failed shingle. It comes from a ridge of ice at your roof's edge that traps melting snow, forcing water backward under the shingles and into your attic, walls, and ceilings. By the time you see a stain, the damage has been growing for weeks.
Lynnwood's freeze-thaw cycles make ice dams a real threat here, even though our winters are milder than the Midwest. Here is how they form, how to spot the damage, and how to stop them.
What Is an Ice Dam and How Does It Cause Water Intrusion?
An ice dam is a thick ridge of ice that builds up along the eaves, the coldest part of the roof. It forms when heat escaping from the house melts snow on the upper, warmer roof. That meltwater flows down to the cold eave, refreezes, and gradually builds a dam. Behind the dam, a pool of liquid water collects. With nowhere to drain, it backs up under the shingles, seeps through the roof deck, and drips into the attic and wall cavities below.
Shingles are designed to shed water flowing downward, not water pushed upward. That is why even a roof in good condition can leak badly behind an ice dam.
Why Ice Dams Form on Lynnwood Roofs
Our region's winter pattern is almost ideal for ice dams: snow followed by daytime melting and nighttime refreezing, repeated over days. Homes with warm attics are the most vulnerable. Recessed lights, unsealed attic hatches, ductwork, and thin insulation all let house heat warm the roof deck. Complex rooflines with valleys and dormers create spots where snow and meltwater collect. North-facing roof slopes, which get little sun, hold snow and ice far longer.
Warning Signs of Ice Dam Water Intrusion
- Thick icicles hanging from the eaves, especially large or uneven ones
- A visible ridge of ice along the roof edge with snow above it
- Water stains on ceilings near exterior walls
- Damp or sagging soffits
- Peeling paint on exterior walls below the eaves
- Musty odors in upstairs rooms or the attic
Because the water enters behind walls and above ceilings, the visible stain is often far from the actual entry point. Our moisture intrusion inspection uses thermal imaging and moisture meters to trace the water path back to its source.
How to Prevent Ice Dams
- Improve attic insulation. Keep attic floor insulation deep and even so house heat stays in the living space.
- Seal air leaks. Caulk and foam around recessed lights, plumbing vents, chimneys, and the attic hatch.
- Ventilate the attic. Balanced soffit and ridge ventilation keeps the roof deck cold and uniform.
- Clean gutters before winter. Clogged gutters trap water that freezes into the start of a dam.
- Use a roof rake safely from the ground. Removing the lower few feet of snow after storms reduces the raw material for dams. Never climb onto an icy roof.
Pro tip: on a snowy day, look at neighborhood roofs. Houses with bare patches high on the roof and snow at the eaves are melting from escaping heat, the classic ice dam setup.
What to Do If You Already Have an Ice Dam
| Safe Actions | Actions to Avoid |
|---|---|
| Use calcium chloride ice-melt in a nylon stocking laid across the dam | Chipping at the ice with an axe or hammer |
| Rake snow off from the ground with a roof rake | Climbing onto an icy roof |
| Place buckets under active indoor drips and move valuables | Ignoring a small drip until it grows |
| Call a professional for steam removal | Using rock salt, which damages shingles and plants |
Long-Term Fixes
The permanent cure for ice dams is a cold roof: seal air leaks, upgrade insulation, and ensure proper ventilation so the entire roof deck stays near outdoor temperature. When re-roofing, ask about ice and water shield membrane along the eaves, which provides a waterproof backup layer under the shingles. Also inspect your roof flashing, since dams often exploit weak flashing at valleys and walls.
What NOT to Do About Ice Dams
Desperation leads to bad ideas. Never chop at an ice dam with an axe or hammer; you will damage shingles and possibly yourself. Avoid climbing onto an icy roof, which is dangerous in any season. Do not install electric heat cables as a first resort without fixing the underlying heat loss; they treat the symptom while your energy bills climb. And skip the rock salt or ice melt tossed on the roof; it corrodes flashing and gutters and barely dents a real dam. The safe emergency move is to clear snow from the lower roof with a roof rake from the ground and call a professional for steam removal if water is actively entering.
Attic Insulation and Ventilation Upgrades
The permanent fix for ice dams is a cold roof deck, achieved with air sealing, insulation, and ventilation working together. Seal air leaks around light fixtures, plumbing stacks, and the attic hatch with caulk and foam; these gaps pump warm air into the attic. Add insulation to reach recommended levels for our climate zone, keeping it clear of soffit vents. Make sure soffit intake and ridge exhaust vents are unblocked so cold air flows under the deck. This combination keeps the roof surface near outdoor temperature, so snow melts evenly instead of forming dams at the eaves.
Ice dam water intrusion rewards early action and punishes delay. Improve your attic this fall, watch your eaves after every snow, and act at the first sign of a dam. If water has already found its way inside, ProLine Leak Fix Pros can trace it to the source. Call (425) 380-0028.
