What are Ice Dams?

Wednesday, December 30 2015 8:40 AM

An ice dam is a thick ridge of ice that builds up along the eaves that overhang the edge of a roof. The problem with ice dams is that they block the gutters, so water from melting snow builds up behind the dam instead of draining off the roof.

This troublesome condition can rip gutters and shingles off the roof. Water can get underneath the shingles and leak down into the walls and ceiling of your home. It may take some time for you to notice problems inside the house, but they can include sagging and stained ceilings, mold growth on wet insulation, peeling and blistering paint, and more. Your home can also suffer costly damage to the plaster, sheetrock, flooring, and even the structure.

What Causes Ice Dams?

If the air in your attic is warmer than the air outside, it will cause the bottom layer of snow to melt before the top does. As the water runs down the roof underneath the snow, it will refreeze when it gets to the cold eaves, instead of draining off into the gutters. This ice will build up along the edge of your roof, blocking the gutters and adding a significant amount of weight to the eaves and guttering. If an ice dam is large enough, it can cause the gutters to break away from the house, pulling down the fasteners, fascia and downspouts with them.

Ice dams are worse after a heavy snow, because the snow itself acts as an insulator and traps the heat below the roof. Here in the Wichita area, we’re no strangers to winter storms that bring several inches of snow, followed by 3-4 days of below-freezing temps. These are conditions for ice dams to develop, if your attic is too warm.

So how does your home’s roof get warm enough to melt snow when it’s below freezing outside? Ideally, your attic and roof should be about the same temperature as the outside air, so proper ventilation is key. Air should be allowed to circulate through the attic between the soffit and roof ridge. Other common reasons heat builds up include warm air leaking from your living space into the attic, uninsulated can lights, inadequate insulation, and bathroom fans that vent into the attic.

How to Prevent Ice Dams from Forming

Air sealing, ensuring adequate ventilation and insulation, and eliminating heat sources will keep the roof temperature down and stop ice dams from developing. You can add an extra layer of insulation to the floor of the attic, install a continuous vent system between the soffit and ridge, and seal up leaks in ductwork.

Re-route any vents the empty into the attic, such as from the dryer or the bathroom fan. These should connect to the exterior of the house. If the dryer vent is near the eaves of the roof, this can also add too much heat to the roof, so keep it closer to the ground if possible. Insulate any other place where air from below the attic can leak in, such as the opening around folding attic stairs, around recessed ceiling lights, and

How to Remove Ice Dams

If it’s too late to take preventive measures, a roof rake can be your best defense against ice dams. It’s shaped like a shovel that’s on its side, and you can stand on the ground and use it to pull the snow off the edge of the roof. Clearing the lower 4 – 5 feet of the roof will give existing ice dams a better chance of melting off, or at least prevent them from getting bigger. You can also try blowing cold air into the attic with a box fan.

Climbing on a ladder is dangerous in snowy and icy conditions, and is not recommended. Other unsafe methods for removing ice dams include chipping away the ice with a hatchet, screwdriver or ice pick, and heating the roof with a heat gun or propane torch. Some people recommend using calcium chloride to melt the ice, but this is dangerous too, because you’ll need to get on a ladder to apply it. Rock salt can damage your shingles and plants below, so never apply it to your roof.

Another common, but not recommended, method is electric heat tap. Placing an electric cable along the edge of the roof isn’t an effective way of melting ice dams, because it takes too much time and electricity. By the time you know you need to use the heat tape, it’s too late for it to work. It’s expensive, the heat can make the shingles brittle, and the cable fasteners create holes in the roof that water can leak through. To make matters worse, the cables can create a barrier that prevents water from draining and actually causes ice dams to form.

Previous: 5 Reasons Why Winter is the Best Time to Build a New Deck Next: Can a Roof be Installed or Replaced in the Winter?

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