Ice Dams: What to Check, What Stops Them, and What to Avoid

Every February, after a snow followed by a few sunny days, the same thing happens on the same houses across Bergen County: a thick ridge of ice forms along the eaves, water backs up behind it, and a stain appears on the ceiling of an upstairs bedroom.

Homeowners usually call a roofer. The roof is rarely the problem.

How an ice dam forms

Snow on the roof melts from underneath when the roof surface is above freezing. The meltwater runs down to the eaves, which hang out past the heated part of the house and are therefore cold, and refreezes there. Repeat for a few days and you have a dam. Water pooling behind the dam works its way under the shingles, which were never designed to hold standing water, and into the house.

The roof surface is warm for one reason: heat escaping from the living space into the attic. So the question is never “what’s wrong with my roof?” It’s “how is warm air getting into my attic?”

Why Bergen County houses are prone to it

• Cape Cods with finished upstairs rooms. The sloped ceilings leave almost no room for insulation and no path for ventilation. These are the worst offenders.
• Split-levels and colonials from the 1950s and 60s with the original attic insulation, often thin, compressed, or pushed aside by decades of storage and cable installers.
• Recessed lights, bathroom fans, and attic hatches that leak warm air directly into the attic. A single uninsulated attic hatch can do more damage than a whole roof’s worth of thin insulation.
• Bathroom fans that vent into the attic instead of outside. Warm, moist air is the worst possible thing to dump up there.

What to check this fall

1. Go into the attic on a cold morning. If it feels noticeably warmer than outside, you have a heat-loss problem.
2. Look at the insulation depth. If you can see the tops of the ceiling joists, it’s inadequate for our climate.
3. Find the leaks. Attic hatch, recessed lights (older cans are often not rated for insulation contact), plumbing and wiring penetrations, the top of interior walls, chimney chases.
4. Check the soffit vents under the eaves from outside. If they’re painted over, blocked by insulation from inside, or simply absent, the attic can’t ventilate.
5. Confirm bathroom and dryer fans vent outside, through the roof or a gable wall, not into the attic.

What actually works, in order

Air sealing first. Seal the attic hatch with weatherstripping and a foam lid, caulk or foam around every penetration, and cover recessed lights with rated boxes. This is the highest-return step and the one most contractors skip.

Then insulation. Bring attic insulation up to the level recommended for our climate zone; for most Bergen County attics that means substantially more than what was installed originally. Blown-in cellulose or fiberglass over the existing layer is typical. Don’t bury the soffit vents; use baffles to keep the air path open.

Then ventilation. Continuous soffit vents paired with a ridge vent let outside air wash the underside of the roof deck and keep it cold. Ventilation alone, without air sealing and insulation, doesn’t fix the problem; it just moves warm air through faster.

Ice-and-water membrane under the shingles along the eaves is now standard on reroofs in New Jersey. It doesn’t prevent dams, but it keeps the water that backs up from reaching the sheathing. If you’re reroofing anyway, make sure it’s specified.

Incentives for air sealing and insulation change frequently; New Jersey’s Clean Energy Program and the local utilities have offered residential programs for exactly this work. Worth checking before you hire anyone.

What to avoid

• Don’t chip ice off the roof with a hammer, hatchet, or shovel. You’ll take shingles with it.
• Don’t salt the roof. Rock salt corrodes flashing and gutters and kills whatever’s planted below.
• Don’t let anyone pressure-wash or hot-water-blast the dam unless they’re an experienced ice dam removal contractor using steam, which is the correct method.
• Don’t rely on heat cables as the fix. They can help a chronic trouble spot, but they treat the symptom, cost money to run, and don’t address why the roof is warm.
• Don’t go on an icy roof. Obvious, and still a cause of serious injuries every winter.

When to call someone, and who

• Water is actively coming in: a steam-removal ice dam contractor can clear the dam safely. Pulling snow off the lower few feet of roof with a roof rake from the ground also helps in the short term.
• You want it to stop happening: an insulation and air-sealing contractor, or a home energy auditor, not a roofer. Ask specifically about air sealing, not just insulation depth.
• Shingles or flashing are damaged: then a roofer, after the attic is fixed.

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Reviewed October 2026. General homeowner information; attic and roof work carries real safety risks, and heavy ice or snow loads on a roof should be assessed by a professional.