There are basically 3 types of roof leaks. The first type is where water is leaking through the roof system while it is raining. This could include leaks due to improper installation of the shingles, damaged or deteriorated shingles or poor flashing details at chimneys and dormers. It may even be due to damaged window sills or improper siding installations or severe wind driven rain. These are external leaks which can usually be repaired by a roofer. If it’s a newer roof this could be workmanship related and may be covered under warranty.
The second type of leak is caused by ice dams. You would typically experience this type of leak in the spring thaw or on sunny or mild winter days. Older homes are especially prone to this type of leaking due to our extreme climate and weather patterns. Ice dams will generally form at the eaves edge of a house as well as in valleys. When snow melts the water runs down the roof re-freezes at the overhangs and forms an ice build up. As more snow melts, more water runs down the roof and meets the ice build up or dam and backs up under the shingles and into the attic. The melting snow is often caused by warm, moist air escaping into the attic due to a poor vapour barrier. This type of leak is not workmanship related and is not covered under labour warranties.
The best way to prevent or reduce ice dams is to eliminate or reduce the amount of warm air that is escaping into the attic and to reduce the relative humidity in your home. Improving the vapour barrier and sealing off attic air leaks is the number one step to take to solve these issues. Another way to deal with the problem, but is not a solution, is having the snow removed from the roof by a reputable snow removal expert, so that you eliminate or reduce the source of water. Having proper ventilation is an important factor on a roof but it is not a solution for this type of problem. Ventilation is not effective in removing moisture from an attic space in the winter. Installing ice and water shield is a good idea but again it is not a cure. Ice shields and ventilation do not address the root problem, which is heat and moisture escaping into the attic due to a poor vapour barrier. Heat cables have also proven to be ineffective in managing ice dam problems.
The third type of leak is caused by condensation or frost build up in the attic. Frost and ice can build up on the underside of the roof sheathing or in wall and roof cavities. The frost is formed by warm moist air leaking into the cold attic space. Bathing, cooking, laundry and body heat all contribute to the moisture in the air. As this warm moist air rises it enters the attic through poor or non existent vapour barriers, attic access hatches, poorly ventilated bathrooms and kitchens etc. The more heat loss there is the more frost can build up. This frost may come and go as the winter temperatures fluctuate from extreme cold to milder temperatures without anyone noticing it. In prolonged cold snaps excess amounts of frost will form. When this frost melts in warmer Manitoba weather it may leak into the living space, damaging the ceilings and walls, form mold or mildew and cause wood rot.
Why now and never before you ask? Your attic insulation and vapour barrier may have gradually become less effective through the years. Also as we upgrade our windows, furnaces and weather stripping we are containing more warm moist air in the home and forcing that air to rise up into the attic which in turn may develop into frost. To prevent frost from developing in your attic you must eliminate or reduce the amount of air leakage into the attic. Next you should try to reduce the relative humidity in the living space. As stated earlier proper ventilation is important but it only deals with the symptoms and not the source of the problem. This type of leak is not workmanship related and is not covered under labour warranties. If your roof only leaks in the spring thaw and does not leak when it rains then it probably isn’t a roof leak.