Ice Dams in York County: What Causes Them and What Gutter Guards Can't Fix

Every winter, somebody in York County finds a brown stain on a bedroom ceiling after a snow and blames the gutters. The fix people reach for is a new gutter or a gutter guard. It usually isn’t the answer. An ice dam is a heat problem that happens to show up at the edge of the roof, and the lasting fix is mostly in the attic.

How an Ice Dam Forms

The Department of Energy’s Building America program explains it plainly. Heat leaking out of the house warms the roof deck under the snow, the snow melts, and the water runs down until it hits the cold edge of the roof past the outside wall. There it freezes. The ice builds into a ridge, and the next round of meltwater backs up behind it, under the shingles and into the house. It takes two things: below-freezing weather and snow that stays on the roof. Snow itself acts like a thin blanket, which helps the roof deck stay warm enough to melt it from underneath. (DOE Building America Solution Center)

The same source names the usual culprits: air leaking from the living space into the attic, too little insulation, poor attic ventilation, and ducts or heating equipment sitting in the attic. Ice dams can also form in valleys and around chimneys, not just at the gutter line.

What Winter Looks Like Here

York County isn’t Minnesota, and ice dams here come and go with the winter. The NOAA weather station south of York averages about 24.6 inches of snow a year, most of it in January and February. It also averages about 120 nights below freezing but only about 13 days that stay frozen all day. (NOAA NCEI 1991-2020 normals) That means snow that sits for a few days and gets melted and refrozen over and over, which is the pattern that feeds an ice dam.

Building codes set snow loads town by town. Glen Rock’s code, for example, sets a ground snow load of 30 pounds per square foot (Glen Rock Ordinance 428), and DOE says ice dams are “likely” once ground snow loads pass 30. So here they’re an occasional problem, more likely in a snowy winter and on houses that leak heat. Houses with finished half-story bedrooms tucked under the roof are prone to them, since the ceiling sits close to the roof and there’s little room for insulation (Center for Energy and Environment).

The Lasting Fix Is in the Attic

Air sealing comes first. DOE calls fully sealing the ceiling the most important step, followed by insulating and ventilating the attic, with vents at the soffits and near the ridge. (DOE Building America Solution Center) ENERGY STAR lists where the leaks usually are: around chimneys and furnace flues, plumbing vents, recessed lights, the attic hatch, wiring holes and dropped soffits. Dirty or darkened insulation is a sign air is moving through it. (ENERGY STAR attic air sealing)

ENERGY STAR also has two warnings worth repeating for older York County houses. Some old attics have vermiculite insulation, which may contain asbestos and should be tested before anyone disturbs it. And once a house is sealed tighter, a combustion safety test on the furnace, boiler or water heater is a good idea. If your attic has knob-and-tube wiring, that’s a job for a professional, not a weekend with a bag of insulation. You’ll find insulation contractors on our /drywall-insulation/ page.

Ice and Water Shield

Ice and water shield is a self-adhering rubberized membrane that goes on the roof deck under the shingles at the eaves, and often in valleys. It won’t stop an ice dam from forming. It’s a backup that keeps water from getting into the house when one does. The building code language Pennsylvania uses (IRC R905.1.2) calls for an ice barrier where there’s a history of ice forming at the eaves, running from the edge of the roof to at least 24 inches inside the exterior wall line (PA UCC ice barrier reference). Manufacturer instructions say the same thing: Owens Corning’s directions run its membrane from the eave to a point 24 inches inside the exterior wall, over the drip edge, and 18 inches each side of a valley (Owens Corning WeatherLock G instructions, 2019). Your township’s code office can tell you what it requires on a reroof.

Clearing Snow Without Making It Worse

A roof rake used from the ground is the safe tool. Massachusetts emergency officials put the rules well: pull snow from the edge and work upward, leave a couple of inches rather than scraping down to the shingles, stay off the roof and off icy ladders, and keep the rake well away from power lines. (Massachusetts Emergency Management Agency) Watch where you stand. Knocking down a big icicle can bring heavy ice down on you.

Don’t chip. A University of Minnesota extension fact sheet said decades ago that you should “never chop through the ice down to the shingles or use a blow torch” (University of Minnesota Extension), and the advice hasn’t changed. If the dam is big or water is already coming in, call a roofer or a snow removal crew rather than climbing up yourself.

Gutter Guards and Heat Cables

Gutters don’t cause ice dams, and gutter guards don’t prevent them. Even a gutter guard maker says so: LeafFilter’s own blog says “gutter guards will not stop ice dams from forming,” and that meltwater can sit on a guard and freeze (LeafFilter). A roofing manufacturer adds that removing gutters won’t stop ice dams either, and that the weight of the ice can pull a gutter off the house (Interlock Roofing). What a clean gutter does do is give meltwater somewhere to go on a thaw day. So guards can be worth it for leaves, as long as nobody sells them to you as an ice dam cure.

Heat cables keep a melted channel open so water can drain. They don’t fix the cause. A Minnesota energy nonprofit tells homeowners flatly not to use them for ice dams, citing wear on the roof and the cost to run them (Center for Energy and Environment). If you do install them on a problem spot, have an electrician wire them: a Raychem de-icing system spec notes that electrical code requires ground-fault protection on every heating cable circuit (Raychem IceStop specification).

What to Ask Before You Hire

• Roofer: Will you install ice and water shield at the eaves and valleys, and how far up the roof? Will you check the attic ventilation and tell me if it’s short? Who pulls the permit?
• Insulation contractor: Will you air seal before adding insulation, and where? Will you check for vermiculite and do a combustion safety test after?
• Gutter installer: What does this guard do with snow and ice? If the answer is that it stops ice dams, keep shopping.
• Anyone selling heat cables: Is this a drain path or a fix? Who’s doing the wiring?

If you only do one thing this winter, go up into the attic on a cold day after a snow and look for dark or frosty patches in the insulation. That’s where your ice dam starts, and it’s a lot easier to fix from inside than from a ladder in February.