Why do ice dams form on North Shore roofs?
The cause is heat, not cold. Warm air from the living space leaks into the attic. It warms the underside of the roof. Snow on that warm part melts, even on a freezing day.
The melted water runs down the slope. At the eave, the roof hangs over open air. Nothing warms that part. The water refreezes there and builds a low ridge of ice.
Do that for a few days and the ridge grows. Behind it sits a shallow pond of standing water. Snow on top hides the whole thing from the street.
Homes on the North Shore see this every winter. Thaw and freeze cycles come through often here. A roof can build a dam, lose it, and build it again inside one month.
Why does the water get inside?
Shingles are built to shed water that runs downhill. Each course overlaps the one below it. Gravity does the work and the laps stay dry.
Standing water breaks that rule. It sits against the laps and creeps sideways and upward. Wind pushes it further. It finds the nail holes and the gaps at the eave.
Once past the shingles, the water soaks the wood and runs along a rafter. The stain shows up on a ceiling far from the leak. People often look for a hole in the wrong room.
What does not fix an ice dam?
Chipping the ice with a hammer or an axe breaks shingles. You cannot see what is under the ice. Damage done in February shows up as a leak in April.
Salt tablets and rock salt stain siding and eat metal. Gutters, drip edge, and flashing all corrode faster after repeated salting.
Heat cables melt a narrow channel. That channel can help in an emergency. It does not stop the dam and it adds a power bill every winter.
Raking snow off the lower roof from the ground is safer than climbing. It buys time. It still treats the symptom rather than the cause.
What actually stops them?
Two things stop ice dams. Keep the roof cold, and give water a protected path if it ever backs up. Everything useful sits under one of those two headings.
A cold roof starts with air sealing. Gaps around light fittings, hatches, wiring, and bath fans leak warm air upward. Sealing those is usually the cheapest step with the biggest effect.
Insulation comes next. Even depth across the whole attic floor matters more than a thick pile in the middle. Baffles at the eaves keep the insulation from blocking airflow.
Ventilation finishes the job. Intake at the soffit and exhaust at the ridge let outside air wash the underside of the roof. That keeps the deck near the outdoor temperature.
The protected path is eave protection. A self adhering ice and water barrier goes on the lower courses before the shingles. It seals around nails and holds back standing water.
- Seal the gaps where warm air leaks from the house into the attic.
- Insulate the attic floor to an even depth, with no bare patches.
- Fit baffles so insulation never blocks the soffit vents.
- Balance intake vents at the eaves with exhaust at the ridge.
- Install ice and water barrier at the eaves whenever the roof is redone.
- Keep gutters clear in the fall so meltwater has somewhere to go.
When is it a roof problem and when is it an attic problem?
If the shingles are sound and young, the attic is usually the place to start. Air sealing, insulation, and ventilation cost less than a new roof.
If the roof is old, the eaves have no barrier, and the ceiling stains keep coming back, the two jobs belong together. There is no point in putting a new covering over the same warm attic.
A roofer can tell you which case you are in after a look at both sides. The attic tells as much of the story as the roof surface does.
What should you do during an active leak?
Move furniture and rugs clear. Put a bucket under the drip. If a ceiling is bulging with trapped water, pierce it at the lowest point so the water drains in one spot.
Do not climb a ladder onto an icy roof. A fall costs more than any repair. Photographs from the ground and from inside are enough for a roofer to work with.
Once the weather settles, get the roof looked at. A dam that came through once will come through again next winter unless something changes.
Ice dams are a yearly fact of life on this coast, but a ceiling stain is not. If water came in last winter, have the roof and the attic looked at together before the cold returns. See roof repair or get in touch.