What Causes Ice Dams in Pennsylvania and How to Stop Them.

If you have ever seen a thick ridge of ice built up along the edge of a roof, with icicles hanging off the gutters, you have seen an ice dam. They look almost decorative. They are not. Ice dams are one of the most common causes of winter roof leaks in Pennsylvania, and the homes most at risk are exactly the older, less-ventilated ones common across our region. Here is what causes them and what actually stops them.

How an ice dam forms

An ice dam is a heat problem disguised as an ice problem. It works like this. Snow sits on your roof. Heat escaping from your living space into the attic warms the underside of the roof deck, which melts the bottom layer of that snow. The meltwater runs down the roof until it reaches the eave, the overhang past the exterior wall, which stays cold because there is no warm attic beneath it. There the water refreezes. Repeat this over a few days and you build a dam of ice at the edge. Once the dam is there, new meltwater pools behind it, backs up under the shingles, and finds its way into the house.

Why central and western PA homes are prime targets

Our winters give ice dams everything they need: enough snow to supply the meltwater and enough cold to refreeze it at the eaves, over and over. The higher-elevation parts of our service area, like much of Cambria County and the eastern edge of Westmoreland County, get hammered with snow. And a lot of the region's older housing has under-insulated, poorly ventilated attics, which is exactly the condition that lets heat reach the roof deck and start the cycle.

The damage they do

Ice dams cause leaks that show up as stains on ceilings and walls, usually near exterior walls. Behind the scenes they soak insulation (which then stops insulating), rot the roof decking and fascia, and can tear gutters right off the house under the weight of the ice. The leak you see in February is often the cheap part. The rotted decking and ruined insulation you do not see cost more.

How to actually prevent them

The real fix for ice dams is not chipping at the ice every winter, it is keeping the roof deck cold so the snow does not melt unevenly in the first place. That comes down to three things, and a good roofer addresses all of them:

Attic insulation. Enough insulation on the attic floor keeps household heat in the house instead of letting it warm the roof deck.

Ventilation. Balanced intake at the soffit and exhaust at the ridge keeps cold air flowing across the underside of the deck, so it stays near the outside temperature. This is why soffit and ventilation matter so much, and why we look at them on every roof.

Ice-and-water shield. When we install a new roof, we lay a waterproof membrane along the eaves and in the valleys. Even if a dam forms, this membrane blocks the backed-up water from reaching the deck and the inside of your home. It is your last line of defense, and it is standard on every roof we build.

What not to do

Do not climb up and start smashing at the ice with a hammer or a shovel edge, you will damage the shingles and probably yourself. Do not run a torch up there. If you have an active leak, a roof rake used carefully from the ground to pull snow off the lower few feet of roof can reduce the supply of meltwater. But the lasting fix is insulation, ventilation, and a properly built roof, which is worth a conversation before next winter.

CTA

Get ahead of next winter. Call Nolan at (814) 312-8555 for a free roof and ventilation inspection.