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What is Ice Damning & How Do You Prevent It?

By August 28, 2018September 5th, 2018FAQ

Ice Damning

While it’s in the 80’s F (30 C) and sunny….Why talk about a phenomia that only occurs in the winter? Simply because re-roofing is the only time you can effectively address its damaging effects.

Ice damning occurs when snow is warmed, by the sun or heat loss from your home, and melts and runs down the roof until it hits an unheated overhang or dead valley where it re-freezes and starts to form a ridge or dam.  Subsequent freeze-thaw cycles can create large dams that hold back hundreds of litres of water. This allows the water to create very powerful hydraulic pressures that can force water back under the shingles with potentially damaging results.

The best way to prevent this is to make sure your roof is constructed for this harsh onslaught of ice and snow.  Here are a few tips on what should be included in your roofing estimate – starting at the eaves and working our way up to the ridge. 

  1. Dripedge – usually a piece of aluminum bent in an “L” shape that protects the edge of the plywood and directs the water into the eavestrough. 
  2. Ice and Water Shield – this is a black “sticky” paper that is used to protect the eaves area from ice buildup (into a dam) which in turn allows snow melt to be forced under your shingles and into your home – not cool.  Ice and Water Shield should also be used in other vulnerable areas where snow can accumulate such as valleys, skylights, dormers, low slope areas, chimney’s and pipes to name a few. The principle here is straight forward added protection to vulnerable points in your roof.
  3. Underlayment (synthetic is best) to the balance of your roof. This layer provides a second line of defense against ice, snow and wind driven rain. 
  4. On very low slope or flat areas the only effective protection is to use flat roof membrane (E.P.D.M. or T.P.O.) that is designed to have snow or water actually sit on the roof. When “tying into” a shingle roof; the flat roof extends under the shingles by 36” or more. (More on this in a future article)
  5. Historically lead and copper were also used in low slope areas as well. These are still excellent options but somewhat pricey and usually reserved for institutional work or the well-heeled with a classic style of architecture.

Here’s the main point – the time to protect your home from ice damming is when you are re-roofing or building new – everything is open and easily accessible for these various techniques to be deployed. Please make sure your roofing contractor is aware of any trouble areas and has an effective strategy for protecting them.  If they minimize any of your concerns around ice damming find a new company that is focused on prevention.

We’ll discuss heating cables, snow rakes and when to call a contractor to remove excess snow in a future article.