Ice Dams refer to the build-up of ice and icicles on the edges of roofs after snow storms. These ice dams present several hazards including potential injuries to pedestrians from falling ice, as well as water damage to buildings from melting ice that seeps under the roof covering. As ice starts to build up on the edge of a roof, it can grow significantly in size as the dam prevents melting snow from draining to the gutters.
What Causes Ice Dams to Form
Ice dams develop after a snow storm, when the outside air temperature is below freezing, and the temperature within a buildings attic (e.g. the space between the ceiling and the roof) is above freezing. The warm air inside of the attic causes snow on the roof to melt. As the water from snow melt travels towards the edge of the roof it freezes (as the edge of the roof isn’t exposed to the warm air within the attic space).
How Can You Prevent Ice Dams
The most effective long-term solution is to keep heat out of the attic (e.g. improve insulation), as well as to promote ventilation under the roof deck to keep it as cold as possible. There are a number of ways to ventilate the attic – often the use of soffit or gable vents for intake, and several conventional roof vents for exhaust air, is the most practical approach.
Improving insulation in the attic can assist in preventing ice dams. Penetrations in the ceiling (e.g. to accommodate lighting fixtures, plumbing, chimneys, etc.) should be sealed (using caulking or a spray-on foam sealant). You should have 12” to 14” of fiberglass or cellulose insulation. If you have only 8” of insulation – add more. Look for ways to seal access hatches – apply additional insulation, use rubber gaskets as sealants around the edges, and the like.
Keep gutters clean of fallen leaves and debris before the first snowfall. Also check your downspouts to ensure they are not obstructed or damaged. Melted snow has nowhere to go if your gutters are clogged.
Use heat tape, applied in a zig-zag (serpentine) pattern along the roof edge as well as inside the gutter and down into the downspout. This should be done only if the other solutions prove to be ineffective.
During heavy snow try to remove 4 feet of snow away from the roof edge, using a roof rake. A roof rake is like a shove turned on its side with a long handle, allowing you to pull snow off the roof while you stand on the ground. Avoid standing on a roof to remove snow – the risk of falling off the roof is too great.
If ice accumulation is severe, hire a specialty contractor who has the skills and equipment to remove ice buildup (using steam sprays to soften and melt the ice).
Summary
To prevent ice dams from forming on the roof we need to keep the attic space cold. Three steps to do this include:
- Seal penetrations between the ceiling and the attic (e.g. caulk around lighting fixtures, ceiling fans, access hatch, chimneys, etc.).
- Add extra insulation on top of the ceiling to minimize heat penetration through to the attic.
- Improve attic ventilation – add soffit vents for intake and standard roof vents for exhaust air.
Additionally, we should:
- Remove about 4 feet of snow using a roof rake with a long handle. Stand on the ground!
- Use heat tape in a serpentine pattern if all else fails.
- Hire an experienced contractor to remove ice dams (using steam) that have already developed. Most often, chopping away the ice yourself will damage the roof and cause personal injury.
