Our Canadian Winters have their frosty reputation for good reason. These extreme temperatures can affect the condition of your home and how it functions.
Your roof is one of the most important lines of defense between you and the natural elements. It helps keep warm air locked in during the winter months and prevents snow, rain or the cold from penetrating the exterior of your home.
This is an ideal time to examine your attic for frost accumulation. Look for excessive frost or staining of the wood on the underside of the roof.
Ice dams on the exterior surface of the roof can be a problem, particularly for low-sloped roofs with an overhang. This is the result of snow accumulation on the roof and is more common on poorly insulated homes. After a snowfall, heat escapes from the attic and melts the snow on the roof. The water runs down and encounters the snow on the overhang, which has not melted because there is no attic below it. The water, which meets this snow, will freeze forming a dam at the lower edge of the roof. This moisture can then back up beneath the shingles and result in damage below. A well-insulated and ventilated attic will help reduce this problem.
If you notice frost accumulation on the underside of your roof or ice dams on the exterior consult the fact sheet found here http://www.cmhc-schl.gc.ca/en/co/maho/gemare/gemare_001.cfm from Canada Mortgage and Housing Corporation titled "Attic, Venting, Attic Moisture and Ice Dams."
Information courtesy of Canadian Residential Home Inspections