Ice dams on Horsham-area homes: why do they happen and how do you stop them?

How an ice dam actually forms

Picture the roof in two parts. The main slope sits over the attic, and if warm air from the house is getting up there, the roof deck over it is above freezing even on a cold day. The bottom couple of feet hang out past the wall over the gutter, with nothing warm under them. That edge stays as cold as the air.

Snow on the warm part melts from underneath and runs down the roof. When it reaches the cold edge it freezes. Day after day the ice builds into a ridge, the dam, and the next round of meltwater pools behind it. Shingles are made to shed water running downhill, not to hold back a puddle, so the water works its way up under them and into the house.

That's why the giveaway isn't the snow, it's heat. Two houses on the same street can get the same storm, and the one with the warm attic gets the icicles and the stained ceiling. Our winters make it worse: we swing above and below freezing over and over, so the melt-and-refreeze cycle runs all season instead of once.

What we see on Horsham-area houses

Most of the ice dam calls we get are on the houses that went up after the war: the Capes, ranchers and split-levels in Willow Grove, Warminster and around Horsham. They weren't built with much attic insulation or soffit venting, and what insulation they have has often been packed down or pushed over the vents over the years.

Capes with a finished upstairs

The Cape is the classic ice dam house. The upstairs bedrooms are built into the roof, with short knee walls on the sides and a sloped ceiling that follows the rafters. There is hardly any room for insulation in that slope, and the little attic spaces behind the knee walls leak warm air straight onto the underside of the roof. We often see the ice line up exactly with where those bedrooms are.

Ranchers and the things that heat the attic

On ranchers it's usually a mix of small things: bathroom and kitchen fans that dump warm, wet air into the attic instead of outside, recessed lights in the ceiling below, an attic hatch with no weatherstrip, and soffit vents blocked by insulation. Each one adds a bit of heat to the roof.

Older borough houses in Hatboro have their own version: thin insulation, board sheathing and mature maples and oaks that keep the north slopes shaded, so snow sits there longest and gutters fill with leaves in the fall. Clogged gutters don't cause ice dams on their own, but they give the ice a head start.

(Question for Jim: what you usually find in the attic on houses with ice dam leaks around here, and roughly how bad last winter was for ice dam calls)

You have an ice dam today: what to do safely

1. Pull the snow off the bottom of the roof. Use a roof rake with a long handle, standing on the ground, and clear the lower few feet of the roof above the ice. No snow up there means no meltwater feeding the dam. Work from the side, not right under the edge, so nothing slides onto you.
2. Leave the ice alone. Do not chip it with a hammer, a shovel or an ice pick. The ice is frozen to the shingles, and you will tear them off and gouge the roof, which makes the leak worse.
3. Stay off the ladder. A ladder on ice against a gutter full of ice is how people get badly hurt in winter.
4. Catch water inside. Buckets and towels under any drip, and turn off the power to a light fixture if water is near it.
5. Take photos. The ice from the ground and any stains inside. Many homeowners policies treat interior water damage from ice dams differently from the roof itself; ask your insurer.

Skip the rock salt: Rock salt thrown on a roof eats at gutters, flashing and the plants below. If you want to melt a channel through the dam, a calcium chloride ice melt product made for the job is the usual choice; read the label.

If water is coming through the ceiling, call us any time at (215) 824-6932. (Question for Jim: do you remove ice dams yourselves (for example with steam), or do you deal with the leak and fix the cause once the ice is gone)

How to stop ice dams for good

The goal is a cold roof: an attic that stays close to the outside temperature, so the snow melts evenly or not at all. In rough order of what tends to do the most:

• Seal the air leaks into the attic. Around the hatch, recessed lights, plumbing and wiring holes, and the tops of the knee walls on a Cape. Warm air leaking up does more damage than thin insulation alone.
• Add insulation on the attic floor. If you can see the tops of the ceiling joists, there is not much there.
• Vent the attic properly. Cool air in at the soffits, under the overhang, and out at the ridge. Baffles keep the insulation from blocking the soffit vents.
• Send fans outside. Bathroom and kitchen fans should vent through the roof or a wall, not into the attic.
• Keep the gutters clear and pitched. Clean them after the leaves drop. Sagging gutters that hold water freeze solid; see gutter installation if yours are past fixing.
• Ice and water barrier at the eaves when the roof is redone. It is a stick-down membrane under the shingles along the lower edge, and it stops ice dam water from getting in. We put it along the eaves and in the valleys on replacements.

Heat cables along the roof edge can help on a problem spot, but they treat the symptom and they use power all winter. If the attic is the cause, fix the attic first. (Question for Jim: do you do attic ventilation work (soffit and ridge vents) yourselves, and who do you send people to for insulation and air sealing)

If you had a leak last winter, a free roof inspection before the snow comes is the time to find out. We check the eaves, the flashing and the attic, including signs like frost on the nails, and show you photos.

One ice dam leak we fixed

(Question for Jim: one recent ice dam job you are comfortable publishing: town (Horsham, Willow Grove, Hatboro or Warminster), house type, where the water came in, what you found in the attic, what you repaired and what it cost or a price range)

When you don't need a roofer for ice

A few small icicles hanging off the gutters after a sunny day are normal, and if there is no ridge of ice on the roof itself and nothing is staining the ceiling, leave them be. If you do get ice dams but the roof itself is sound, the work that stops them is mostly in the attic: air sealing and insulation, which is an insulation contractor's job more than ours. Many utilities offer home energy checks that will point out the leaks. Call us when there's water inside, damaged shingles or flashing, or when the roof is due for replacement anyway and the eaves need ice barrier.

One leak from an ice dam does not mean you need a new roof. Usually it's a roof repair at the eave, plus fixing the cause.

Related questions

How do you remove an ice dam from a roof?

Pull the snow off the lower few feet of the roof with a roof rake while standing on the ground, so nothing feeds the dam, and let the ice melt. Do not chip it, because the ice is stuck to the shingles and you will tear them. A calcium chloride ice melt made for roofs can open a channel; rock salt damages gutters and plants.

Why do I get ice dams every winter?

Usually because warm air from the house is getting into the attic, melting snow on the roof, and the water refreezes at the cold edge over the gutter. Many Capes and ranchers around Horsham, Willow Grove and Warminster have little attic insulation or venting. Air sealing, insulation and better venting stop most of it.

Does an ice dam mean I need a new roof?

Usually not. Most ice dam leaks need a repair at the eave and a fix in the attic, not a new roof. If the roof is near the end anyway, replacing it is a good time to add ice and water barrier along the eaves.

Will new gutters stop ice dams?

Not on their own. Ice dams start with heat from the attic, not with the gutter. Clean, well-pitched gutters help, because clogged or sagging ones fill with ice and give the dam a head start.

Does homeowners insurance cover ice dam damage?

Many policies cover water damage inside the house from an ice dam, and treat the roof itself differently. Coverage varies a lot, so ask your insurer and take photos before anything is cleaned up. We can document the roof side.