Ice Dams: Causes and Prevention
Winter is here again and while it has been fairly mild over all in Calgary, we have had a few periods of cold and snow as well. In December alone we had over 32 cm snow and some very cold temperatures. Our December snowfall combined with the warmer temperatures in January provided the perfect weather for ice dams to form. Sometimes ice dams can melt with warmer temperatures without causing any visible damage to the home. Before we go into practical ways to stop ice dams, let’s take a quick look at what causes them, and the essential steps that must be taken to mitigate the problem.
Ice Dams happen when you have snow on the roof and the heat that escapes from inside your house / attic melts the snow. As snow melts, water runs down the roof, and when it gets to the roof edge (eaves) which are unheated, it once again freezes. As more and more water freezes along roof eaves, the ice builds up, creating ice dams. When even more water runs down, it now has nowhere to go, so it backs up under the shingles, and leaks into your roof.
Winter is here again and while it has been fairly mild over all in Calgary, we have had a few periods of cold and snow as well. In December alone we had over 32 cm snow and some very cold temperatures. Our December snowfall combined with the warmer temperatures in January provided the perfect weather for ice dams to form. Sometimes ice dams can melt with warmer temperatures without causing any visible damage to the home. Before we go into practical ways to stop ice dams, let’s take a quick look at what causes them, and the essential steps that must be taken to mitigate the problem.
Ice Dams happen when you have snow on the roof and the heat that escapes from inside your house / attic melts the snow. As snow melts, water runs down the roof, and when it gets to the roof edge (eaves) which are unheated, it once again freezes. As more and more water freezes along roof eaves, the ice builds up, creating ice dams. When even more water runs down, it now has nowhere to go, so it backs up under the shingles, and leaks into your roof.
The main cause of ice dams is lack of proper attic insulation AND roof ventilation, so it is often ideal to improve both, before resorting to some more extreme measures. Excessive heat venting into the attic from a bathroom fan or clothes dryer that is improperly connected is another common cause.
Proper ventilation of the attic is extremely important for homes in the Calgary area due to the temperature fluctuations and freeze thaw cycle we experience during the winter and the hot summer days we can experience. A properly vented attic has both intake vents, typically installed in the soffit overhang but sometimes low on the roof, with exhaust vents installed near the top of the roof. The Alberta Building Code requires the house to have one square foot of venting for three hundred square feet of ceiling area. Ideally this would be split equally between the intake and exhaust vents.
The first step in solving an ice dam problem is to determine why there is excessive melting of snow on the roof. This can be checked by measuring the temperature of the ceiling with infrared equipment looking for cold spots or even better access the attic space and have a look. If hot air is collecting in the attic due to a bathroom fan or a clothes dryer not venting directly to the outside of the house the solution may be as simple as correcting the vent pipe.
When we go in an attic what we look for is to see if the insulation is spread evenly through the attic with no void areas and measure the depth of the insulation. In older homes is not uncommon to find three or four inches of wood chips between the rafters as the only insulation. New homes being built now will have fifteen inches or more of loose fill insulation. Along with checking the insulation we also look to see if insulation or something else is blocking the intake venting. This is done by looking to see if there is any light coming into the attic from the eaves areas. We look to see if the exhaust vents were cut through the wood roof deck properly and that the vent is centred on the hole. There is no use in having a bunch of vents if they are fully or partly blocked reducing air movement through the attic. We also look to see if there are vent pipes running to the roof from all of the fans and any evidence of air leakage around them.
Once you have an ice dam it can be a difficult problem to re rectify. If water is leaking into the home the most important thing to do is to remove some of the ice to allow the water to flow off the roof. There are a few ways this can be done, all of which are difficult and potentially dangerous and should be left to professionals. The first thing to do is to remove any remaining snow that is on the roof above the ice. This can be done with a snow rake from below or snow shovels from above. If the ice dam covers a large area the fastest and safest way to remove the ice is with high pressure stream. This is done with specialized equipment by trained professionals in a way that removes the ice without damaging the roofing material below. If the problem is smaller and localized a good roofer can use their roofing hatchet and chop channels through the ice that allow the water above to drain off the roof. This can be tricky because the ice bonds to the roof below and if removed too deep the roof can easily be destroyed. Ice melting products can also be spread on the ice to accelerate the melting of the ice. If these products are used they should be checked to insure that they will not damage the roofing membrane.
If the home is prone to ice damming the best time to correct the problem is in the spring. It is fresh in your mind and the problem area will likely still be visible. Correcting the problem in the spring insures it is not forgotten until the following winter when water leaks in again. If we are experiencing a mild winter it is possible to complete repairs during one of our mild periods. However, this depends on the property and the nature of the required work. Most roofing work is best done in any season but winter!