Eliminating Rooftop Ice

A few winters ago, as I was driving down the highway,  I passed the house of a man in the throws of a particularly northern form of desperation. He was at the top of a ladder leaning against his house, using a full-size axe to attack a massive glacier of ice that had formed around the eaves. He was going at it with both hands, chips flying. Never mind that it was absurdly dangerous up there, and never mind that it would take a miracle to shield the shingles from damage. Never mind that the job was obviously torture. The ice had to go at any cost, probably because this guy knew what it would cause later if it remained in place as the weather warmed up.

These ice dams and massive icicles were a regular part of the community hall near my home, but upgrades to insulation and attic ventilation has completely solved this problem.

Ice is beautiful, but more than a little on your roof is a bad thing.

Long stretches of cold weather always lead to rooftop ice buildup on some homes, and this situation shouldn’t be ignored. Besides the danger of ice falling off and hurting someone, rooftop ice often causes leaks in otherwise sound, shingled roofs by preventing the downward flow of water when the weather warms up. Many roof surfaces have almost no ability to seal out pools of water since they’re only good at keeping things dry when gravity is actively propelling water downwards. And the fact that rooftop ice stops this flow and causes pooling is a big problem because it triggers roof leaks.

Excess ice forms on roof eaves for one reason . . .

Too warm roof surfaces are the cause of ice dam buildups on the eaves, and roofs that are too warm may be caused by…

  1. Inadequate attic insulation
  2. Less-than-sufficient attic ventilation
  3. A combination of the two

Either way, the result is the same… roof leaks

  • Excess rooftop heat causes snow to melt on the main part of the roof, even when the surrounding air (and eaves overhang) is below freezing.
  • As melt water trickles downwards, it eventually comes to the eaves which are still below freezing because they have no heated space under them.
  • The melt water freezes and forms a small ridge of ice or icicles. These won’t be noticeable at first, but they’re the seeds of trouble.
  • As the melting-and-freezing process continues, the ice buildup gets larger and larger until it’s high enough to hold back pools of water on days when the temperature rises above freezing.
  • If the downward flow is stopped like this, water will find an alternate route between your shingles and down through your ceiling.
Rooftop ice might look like it’s caused by eavestroughs, but it’s not. The real cause is excess heat escaping from the roof, melting snow when ambient temperatures are still below freezing. As this water drains down and hits the cold, unheated eaves, it freezes, forming an ice dam. Shingle damage and roof leaks result. The longer the cold spell, the bigger the ice build up.

The worst thing about ice-caused roof leaks? No permanent fix possible until spring.

Adding more insulation and ventilation will make your roof surface colder and that’s good, but it won’t get rid of existing ice build up and the leaks it may cause later in the spring. Another problem is that upgrading insulation and ventilation isn’t easy (or even possible) with cathedral ceilings, which are usually associated with the heaviest ice build up. There’s simply no way to get into the attic space to work.

  • In these cases, the best you can do is add 2 to 4 inches of rigid extruded polystyrene foam insulation to the underside of the ceiling, then drywall over it.
  • Even then, it may be necessary to install an electric rooftop heating system along the eaves if the foam isn’t enough to keep the roof cold. You’ll only know for sure next winter.

Another remedial approach is installation of a seamless rooftop membrane all around the eaves.

  • By running the membrane up several feet higher than the area of ice build up, any standing water is prevented from trickling down through the shingles.
  • This fix doesn’t look great when it’s applied over an existing roof, but it’s better than brown water marks on your ceiling.
  • Installation of a roofing membrane called ice and water shield under new shingles during the next re-roofing job does the same thing invisibly.

Rooftop Heating

When it’s not possible to add insulation or boost attic ventilation enough to solve rooftop ice buildup, then some form of rooftop heating system is what you need. The best rooftop deicing system I’ve seen is made in Canada’s Muskoka region of Ontario. It’s effective, invisible and I know from watching it over a number of years that it actually works. Watch the video below to see for yourself. It’s an electric heating system, but there are no cables to see.

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