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Effects Of The Winter And Snow On Your Flat Roof

Residential roofers and commercial flat roofers in Ontario tell us that the effects of winter and snow on most roofs is a major issue not least of which for flat roofs in Ottawa. It’s the same for flat roofs in Toronto and throughout most of Canada. This will be confirmed by most flat roof building owners and general contractors. In order to be proactive about flat roof maintenance it’s a good idea to understand what the potential for damage is. First though some information about snow.

Snow is heavy

Snow has weight – mass. Snow weight is determined by volume and water content. Wet snow is heavier than dry snow. For example: One foot of new snow equates to an inch of ice. 40 inches of dry snow is equivalent to six inches of wet snow in weight. That is why it is important to remove a few inches of snow quickly. When new snow combines with old snow, the weight could exceed the load capacity of a roof which is designed to bear around 20 pounds of snow per square foot.

Bowing and Pooling

Snow builds up easier on a flat roof compared to a pitched roof. This creates stress and puts pressure on the joists, causing the trusses to buckle which in turn gives rise to pooling (ponding) in sagging areas of the roof, as the water has nowhere to go. As the snow melts ponding or pooling occurs thereby increasing the pressure which can impact on secondary systems like HVAC units and cause them to stop working.


If snow is not removed immediately, it will melt and spread out, taking the path of least resistance into cracks and crevices. Though some of it may be evaporated, it will likely refreeze as temperatures drop with sundown. Ottawa roofing contractors explain what happens next: When the water turns to ice it expands and the expanding ice in roof cracks widens the cracks and leads to roof liners being penetrated and broken. The roof then becomes vulnerable to leaks. Such ice dams are a problem for flat roofers in Toronto too where snowfall is prodigious.

Roof leaks

Roof leaks can be avoided by removing snow before it gets to more than 6 inches and before it turns to ice, the weight of which can cause the roof to collapse. Roof repair companies advise that after a heavy snow fall it is a good idea to carry out an inspection inside the home as leaks may not always be obvious. One sign that there may be a leak is the distinctive smell of damp so follow your nose. When inspecting, roof contractors advise turning the lights on as this will increase the chances of spotting damp patches on the ceiling and water or at least moisture, high up on the walls. Roof contractors also advise that a proactive check for leaks in the roof be done in summer. Take a hose pipe onto the roof and see where the water goes.

More clues

Flat roof contractors suggest looking at the ceiling. If the ceiling is spotted or sagging, or if there are cracks, hairline or worse, it could be that the roof is damaged. Similarly, if cosmetic ceiling beams are bowing or are no longer level or parallel, it is probably because they are full of water. This would be the time to call a roof contractor. Furthermore the roof companies advise to check the walls. With the lights on, stand in the doorway and look across the walls to see if there is any bowing and buckling, which should be easy to spot. This is another reason to call in the flat roofing professionals. A further indication of problems is icicles on the edge of the roof.

Be proactive

Flat roofs are more susceptible to damage caused by snow, water and ice than pitched roofs. If your roof hasn’t been professionally inspected in many years, it’s a good idea to invite them over. This can prevent small problems from becoming expensive nightmares. Wolfenburg Roofing has over 25 years of industry experience, including expertise in everything flat roofing. We are a fully licensed and insured residential/commercial flat roofing company in Ontario. For more information or to arrange an appointment visit us at


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