Effects of Snow & Ice on your Roof.

Here in Ontario we get extreme temperatures from hot summer days to cold winter nights. Not only that, but we get huge temperature fluctuations within a single day and winter storms occasionally dump massive loads of snow.

All of this amounts to very harsh conditions for your flat roof, but with a little attention you can minimize the effects of our northern climate.


Remove Ice Dams

In other articles we have stressed the need to make sure your drains are clear of debris but during the winter time ice can present the same problem.

As your roof sits in the sun it gets hotter than the surrounding air. When the temperatures are not too far below freezing this can cause water to melt and begin to run off the roof, however water doesn’t always make it off.

Whether it be that the drain is in a shadier area or just that it’s cold inside, water can often freeze again in or around the drain resulting in an ice dam which reduces or eliminates the effectiveness of the drain.

When an ice dam forms blocking off a drain it can cause increased water and ice buildup, adding to the weight that the roof has to support. It can also lead to other problems such as freeze-thaw and leaks.

Freeze-thaw is when water on the roof melts and is able to creep into minuscule cracks in the roofing membrane where it freezes again. This is the same process which breaks down large rocks and boulders.

As the water freezes in the tiny cracks it expands, pushing the membrane apart more and leaving more space for water to seep in the next time. Over time this process can cause leaks in the roof.

The longer the water is allowed to sit on the roof because of being dammed off from the drain, the longer it has to get into, expand and eventually seep right through cracks in the membrane.

Removing ice dams means that you ensure that there is a clear path for the water to exit the roof. According to the National Roofing Contractors Association, water should not be on your flat roof for more than 48 hours.

In the winter time this means that water needs to be able to flow toward the drain and off the roof. You won’t be able to keep off the water in the bottom most layer of snow, but as soon as it is free from the snow the water should have a clear path off your roof.


Snow Weight

Snow can be heavy. Wet snow in just below freezing temperatures can weigh up to 50 pounds per cubic foot, a little less than water, weighing in at 62 pounds per cubic foot. That can add up to a lot of extra weight for your roof to handle but with the right products and installation it should be up to the task.

This is one reason that we don’t like to install the less expensive, thinner membranes, as we feel that they just don’t hold up to the demands of our climate. Having a single-ply membrane, mechanically fastened roofing system also reduces the weight that the roof must support, as opposed to a ballasted roof (usually relying on river rock to hold the system down).

Roofs in Ontario are made to be able to support the weight of the largest snow fall in the last 100 years plus 40%, however there are a number of things which can affect this calculation.

If you have roofed over an existing roof the new roof will add weight and put your roof closer to the weight load limit, while replacing a roof with newer, lighter roofing membranes will further distance you from that limit.

Under normal circumstances there should be no fear of a roof collapsing unless significant weight has been added since the initial design of the building. The main concern is that the added weight will cause sagging and ponding on the roof which will need to be repaired in the spring by your flat roofing contractor.


Large Icicles

Not only a safety hazard, but often an indication that something on your roof is amiss, large icicles should be investigated as to their source and regularly removed.

Large icicles which reappear in the same places could be an indication of drainage problems which could cause damage to your roof. Whatever their source, large icicles, especially in highly trafficked areas, are a danger for people beneath them and need to be routinely removed to prevent injury and liability.


Final Note

While roofs in Ontario are made to weather our extreme temperature fluctuations and the weight of snow, it is always good to keep an eye on your roof in the winter time to make sure that it is functioning properly.

Small problems like ice dams can quickly lead to extreme ponding and added weight, and should therefore be dealt with as soon as they occur rather than waiting for leaks, which always indicate more extensive measures will be needed.

Be sure to get your roof inspected by a knowledgeable flat roof contractor at least yearly in order to maintain the integrity of your roof.

Contact Northern Seal today to schedule your yearly roof inspection, make repairs or quote a new roof!