Ice dams explained
One of the common findings during home inspections this time of year in Kelowna and the Okanagan is ice damming, especially on detached houses with large roof overhangs. An ice dam is a ridge, or build-up, of ice that forms along the edge of a roof and prevents melting snow from draining off the roof. As the snow on the roof melts, the water runs down the roof and refreezes at the cooler edge, forming a dam. Sometimes large icicles will also form along the roof or gutter edges. As more snow melts, the water continues to build up and freeze behind the dam and can seep under the shingles, causing them to heave or crack, and eventually allowing water to make its way into the house.
Ice dams typically form when there's a large temperature difference between the roof and the air outside. This can happen when the air inside the house (or more specifically, the attic) is warm and the air outside is cold, or when the roof is poorly insulated. The warm air inside the house can cause the snow on the roof to melt, while the cold air outside causes the water to refreeze at the edge of the roof.
Furthermore, clogged gutters contribute to ice dams. Whether it's leaves, sticks, or other debris that are preventing the gutters from draining properly, any decrease in the effectiveness of gutter drainage can cause ice to build up in the gutters, and eventually on the roof edge as well.
Sometimes, when the home has perforated soffits and large roof overhangs, cold air can get into the roof edge area and create a pronounced difference between the two areas. Ideally, we don’t want big temperature differences between the roof and the eaves, or roof-edge-area.
How to prevent ice dams from forming
To prevent ice dams from forming, the key is to make sure the temperature of your roof stays consistent with the temperature of your eaves. To do this, prevent inside air from reaching the attic or roof space by sealing any leaks, upgrading or increasing the attic insulation, and adding ventilation to the soffits. An insulation specialist can help you keep the roof the same approximate temperature as the eaves by ensuring that it’s properly insulated and ventilated. This will help to prevent the snow on the roof from melting and will also help to keep the air inside the house cool. Although it’s not always safe to do so, if your home has a flat roof, it’s a good idea to remove any snow from the roof as soon as possible, as this will help to prevent the build-up of ice dams. This can sometimes be done with a long rake. Be safe and make sure not to stand below the eaves to avoid falling snow and ice.
If an ice dam does form, it is important to remove it (carefully and manually using heat) as soon as possible to prevent water from entering the house. Roof or gutter de-icing cables look like an extension cord but they are heated wires that can be laid across the roof to keep the roof edge warm and prevent ice dams from forming. At Daylight Home Inspections we have had good experiences with deicing cables and have found them to be very quick and effective. But every home is different, and the general approach to insulation and ventilation in roof areas has changed greatly through the years. Depending on whether your home uses an older or newer style of construction will determine the best route for your particular case. Contact your local roof & gutter professional help removing the ice dams if they have already formed.
Typical de-icing cable kits
