Ice Dams in Western New York

What an ice dam actually is

An ice dam is a ridge of ice that builds along the cold edge of your roof and traps meltwater behind it. The water has nowhere to drain, so it sits, finds the seams between shingles, and works its way backwards under them and into the house.

Here is the sequence. Snow sits on your roof. Heat leaking out of your living space warms the underside of the roof deck. Snow on that warmed upper section melts, even when it is well below freezing outside. That meltwater runs down the roof until it reaches the eave — the overhang, which hangs out past the heated part of the house and stays at outdoor temperature. There it refreezes. Repeat that for a week of a typical Buffalo cold snap and you have a dam several inches thick, with a pool of standing water sitting behind it.

The shingles are not failing. Asphalt shingles are designed to shed water running downhill. They are not designed to hold back a pond. No shingle on the market will keep water out under an ice dam.

Why Western New York is so bad for this

Two things stack against us. The first is lake-effect snow — we get deep, persistent snow cover that sits on the roof for weeks instead of falling off. The second is our freeze-thaw pattern. WNY spends a lot of the winter oscillating right around freezing, which is precisely the condition that melts and refreezes water repeatedly. A place that stays at ten below all winter actually has fewer ice dam problems than we do, because nothing melts.

Add in the age of a lot of our housing stock. Pre-war homes in Buffalo, Lockport and the Village of Williamsville were built with little or no attic ventilation and, by modern standards, almost no insulation. Those houses leak heat straight into the attic. That is the fuel for the whole process.

The three things that actually work

1. Air sealing the attic floor

This is the one almost everybody skips, and it is the most important. Warm air escapes into your attic through gaps you cannot see: around recessed lights, at the top plates of interior walls, around plumbing stacks and bath fans, through the attic hatch, down open chases. Sealing those bypasses stops the heat getting up there in the first place. Insulation alone does not do this — insulation slows heat conduction, it does not stop air leakage.

2. Enough insulation, installed properly

Once the air leaks are sealed, insulation keeps the attic close to outdoor temperature. Current recommendations for our climate zone put attic insulation in the R-49 to R-60 range. A lot of the WNY homes we work on are sitting at R-19 or less, often compressed or with bare patches where somebody stored boxes.

3. Balanced ventilation

Cold air needs to move through the attic to carry away any heat that does get up there. That means intake at the soffits and exhaust at the ridge, roughly balanced. A ridge vent with blocked or painted-over soffit vents does almost nothing — there is no intake, so there is no airflow. When we replace a roof we check the soffit intake, because installing a beautiful ridge vent over a sealed soffit is theatre.

And one thing that limits the damage

Ice-and-water shield is a self-adhering waterproof membrane that goes down on the bare deck before the underlayment and shingles. It seals around nail penetrations, so even when water backs up behind a dam, it cannot get into the structure.

New York's residential code requires an ice barrier in areas subject to ice damming, running from the eave edge to at least 24 inches inside the exterior wall line. That is a minimum, not a target. On low-slope sections, in valleys, and on north-facing slopes with heavy shade, we routinely go further than code, because we have seen where the water actually gets in.

Ice-and-water shield does not prevent ice dams. It prevents the ice dam from wrecking your ceiling. Both matter, but they are different jobs.

What does not work (or barely works)

Heat cables

Zig-zag heat cables along the eaves melt a channel through the dam so water can drain. They are a symptom-management tool, not a fix. They cost money to run all winter, they fail, and they do nothing about the heat loss that is causing the problem. Occasionally they are the right call — on a complicated roofline where the real fix is not practical — but they should be a last resort, not a first one.

Roof raking

Pulling snow off the lower three or four feet of the roof does genuinely help in the short term, because it removes the material that forms the dam. Two cautions: do it from the ground with a proper roof rake, never from a ladder in winter, and do not scrape the shingle surface. Dragging a metal edge across cold asphalt shingles knocks granules off and shortens the roof's life.

Chipping the ice off

Please do not. Every winter somebody goes up with a hatchet or a hammer and puts a hole through their own roof. Cold shingles are brittle. If you have active water coming in and need it stopped now, call us.

How to tell which problem you have

Go up in the attic on a cold day, and take a flashlight.

• Frost on the underside of the roof deck means warm, moist air is getting up there.
• Dark staining on the sheathing means it has been getting wet, repeatedly.
• Insulation that is thin, patchy, or matted down is not doing its job.
• Daylight around a plumbing stack or at the top of a wall is an air leak you can see.
• A soffit vent you can see blocked by insulation pushed into the eave is a very common and very fixable problem.

If you find any of that, the fix starts inside the house, not on the roof. If your roof is also near the end of its life, doing the attic work and the roof at the same time is the sensible order of operations — we can get at the eave detailing and ventilation while the shingles are off.