You don’t live in a cave—so why the stalactites?

Ice damming challenges

Darn Ice-Damming.

It’s been a long winter, but summer is almost here. The lengthening days signal that it is time to start planning some of the regular maintenance every building needs to deal with the winters still to come. Have you noticed long, heavy icicles hanging from your home’s eaves this winter? If you did, the building likely has a problem with ice damming. Examining the damage, effecting repairs and solving the underlying problem should be a priority.

Ice damming happens when warm air that rises in a building suddenly hits the frozen roof. Any snow or ice sitting on that roof melts and runs towards the eaves—where it promptly freezes again. That ice plugs the eavestroughs, overflows (hence the icicles) and is often forced into the roof itself. Many think that icicles hanging from the eaves are beautiful, but the water forced into the roof can wind up in the ceiling and walls. Ice damming is often the root cause of problems with mould, rot and even structural failure.

There are several ways to minimise ice damming. Keeping snow off the roof prevents it from melting in the first place. Heat cables can be installed at the base of the roof to prevent water from refreezing at the eaves. However, if the roof is nearing the end of its useful life and in need of rehabilitation, this is an opportunity to address the underlying problem.

Ice damming is indeed a symptom of a larger problem with the roof. Those long, heavy icicles are a sign that a roof lacks proper insulation or ventilation. The more heat escaping from the attic, the more quickly the snow on a roof will melt. The more poorly ventilated the roof is, the less likely the rising heat will dissipate evenly.

What to do? Careful observation and a little research is always the first step: you cannot solve a problem you don’t understand. Get into the habit of comparing the amount of snow on your roof to the amount on the roofs of other buildings in the area. If snow disappears more quickly from your roof, that could be evidence of poor insulation. If the amount of snow is unevenly distributed a few days after a snowfall, your roofing system may be poorly ventilated.

How to fix the underlying problem? Since ice damming is caused by melting snow that quickly refreezes, a solution will limit the amount of heat escaping through the attic while distributing the heat that does inevitably escape evenly across the roof. Be careful—adding too much or the wrong type of insulation or installing it poorly creates its own problems.

Insulating a roof in the wrong way can easily compromise the ventilation. The areas where a roof meets the walls will always be warmer than the peak. Proper ventilation moves heat from the warmer to the cooler areas of the roof, limiting the potential for the snow and ice to melt. In older homes, a lack of ventilation is quite common: exposed rafters or decorative boxed-in soffits with crown mouldings often restrict air flow within the attic. There are ways to improve ventilation that do not comprise the heritage value of your home.

It’s always a good idea to consult a professional. An architect or roofing engineer can help you evaluate the benefits and drawbacks of different solutions. You must consider all of the variables and materials that compose a roof before implementing a solution:a roof is not just a layer of shingles but a system complete with external and internal components.

Written by: Carlo Laforge, Heritage Conservation Adviser.

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