How to Deal with Ice Damming on your Roof
Winter is full of repeated freeze-thaw cycles that can result in an ongoing nuisance — ice damming. Sure, icicles hanging from your house may look pretty but the build-up of ice at your eaves or roof’s edge is bad news. Chunks of ice could fall and hurt someone, and it can be a significant source of property damage.
Ice dams can tear off gutters and loosen shingles. What’s more, because the thick ridges of solid ice can prevent new meltwater from draining off the roof, the water may back up under the shingles and leak into your house, resulting in stained and sagging ceilings, warped floors, peeling paint, soggy and potentially mouldy insulation, and other devastation to your interior finishes and furniture.
This problem is most common on houses with sloped roofs and attics. When sloped roofs are not properly insulated, ventilated or waterproofed, ice dams can occur as meltwater flows down the slope. Homes with flat roofs may have ice or meltwater problems but they typically have continuous waterproofing that contains ice and water.
Since ice dams form over time by on and off periods of melting and freezing, you need to be weary of warning signs. These include large amounts of snow on the roof; visible icicles on gutters, especially dark-coloured ones caused by water coming into your attic, picking up dirt and taking it back outside; and water stains on ceilings.
If you have ice dams, you should not try to remove them as it is difficult to do so easily and safely or with any assurance the roof surface won’t be damaged in the process. (Hacking away with a hammer, chisel or shovel isn’t going to do any good.) Instead, wait for the ice to melt naturally in spring and then address the underlying causes, such as improper ventilation or insulation. You should, however, break off any hanging icicles and blocks of ice immediately to prevent possible injury to people.
To get rid of ice dams for good, ensure your attic is properly ventilated. The building code requires ventilation to be provided at the upper portions of the roof and at the eaves/soffits. Many engineers recommend venting be spread evenly between the soffit and the upper portions of the roof (50-50 split), but the code indicates that up to 3:1 is allowable.
Your attic also needs to be ventilated with outside air so that temperatures generally stay quite cold. This is accomplished by evenly applying insulation on the attic floor and sealing penetrations at pot lights, exhaust fans and pipes.
To guard against future leaks resulting from ice dams, clean leaves out of downspouts and gutters in the fall and keep the snow load on your roof down in winter by periodically raking it. (Do this from the ground using a rake with a telescopic handle, not from atop the roof.) Also, the Ontario Building Code requires that a protective membrane be installed from the eave to 900 millimetres above the eave. This eave protection doesn’t stop ice dams from forming; it’s simply intended to prevent leaks caused by ice dams.