Preventing Ice Dams From The Exterior



Our climate is similar here in Montreal. Our first big snow dump this year fell with westerly winds so the lee sides of homes developed what I like to call ‘Snow Brows’. Theses are big over hangs of snow projecting various distances out form the roof edges.  ‘Don’t slam the door!’ scenarios because a sudden jolt can cause them to drop.

Lots of ice dams developed under theses brows. Most people here don’t do anything about it. They wait it out, expecting it to get even colder, so everything freezes. They think they are ok till next time. We know that’s not true.

We’ve just gotten lucky. Areas here and the north east Us states have gotten a reprieve. We’ve had a warm spell that lasted long enough to melt the roofs clean. Now there is gust a light dusting of snow, but there were some big chunks of ice falling for a few days.




I’ve been doing a lot of attic inspections for Minneapolis homeowners with water leaking in to their houses, and in almost every case I find obvious problems in the attic that should be addressed to either prevent or significantly reduce ice dams.  I mentioned most of the stuff that I look for in last week’s blog about preventing ice dams.

Occasionally I’ll come across a house with no attic space in the areas where heat loss is occurring, or there isn’t access to the attic areas.  In these cases, it probably isn’t cost effective to fix the problems that are causing the ice dams – the ‘repairs’ would outweigh the costs of controlling the ice dams.  In those cases, I recommend ice dam control from the exterior.

Remove The Snow

Reuben Raking Snow Off His RoofIf you rake the snow off your roof, you’ll keep ice dams to a minimum.  This becomes a constant chore, but it’s better than dealing with water leaking in to your house.  Just raking the first several feet of snow from the eaves is usually enough to prevent the formation of ice dams, but in some cases, this will cause ice dams to form higher up on the roof.

I have one very low-sloped section of roof at my own house where even closed-cell foam wasn’t enough to prevent the formation of ice dams, so I get out there with a roof rake and pull the snow off my roof.  This is a perfectly safe way of removing snow, as long as you don’t get too close to your overhead power lines.

This is also a very effective way of preventing ice dams, but it won’t work 100% of the time.  This year,  for the first time ever, I actually had another ice dam begin to form higher up on my roof just past where I had stopped raking.  That was crazy.  I ended up removing almost all the snow on my roof with a super-long roof rake, and that worked very well.

For owners with two-story homes where using a roof rake from the ground isn’t practical or possible, the options are to risk your life getting up on an icy roof to shovel the snow off, hire someone else to risk their life, or install roof de-icing cables as a preventative measure.  I say go with the de-icing cables.

Men Shoveling On Roof

De-Icing Cables

Roof De-Icing Cables Promotional PhotoRoof de-icing cables, also known as heat cables or heat tape, should be a last resort when it comes to preventing leakage from ice dams.  De-icing cables themselves aren’t cheap, it’ll cost money to have them professionally installed, and they’ll cost money to operate – between five and eight watts per foot.  On the flip side, they’re very effective; it’s pretty much a guarantee against leakage from ice dams.  They won’t prevent ice dams, but they’ll keep enough ice melted to create drainage channels for water, if installed properly.

If you choose to install roof de-icing cables yourself, here are a few tips:

  • Measure the areas where you need to install your de-icing cables first, and buy appropriately sized cables.  For a simple 15′ section of roof with no overhang, a gutter, and one downspout with an extension, you will need a 60′ heating cable.
  • Roof De-Icing Cables Real Life The cables should extend 6″ up the roof past the exterior wall line, through the gutters and downspouts, and 2/3 of the way up the valleys.
  • Don’t bother removing the snow from your roof; you could damage your cables, and you could potentially create another ice dam higher up on the roof, defeating the purpose of the heating cables.
  • Don’t expect the snow and ice to melt the way it does in the promotional photo above.  The photo at right, which I took at a real house, is what this stuff is going to look like.  Don’t worry, this is normal.

If fixing the causes of your ice dams isn’t a possibility and you can’t safely remove snow from your roof, install some de-icing cables or de-icing panels.  This is oftentimes the most cost-effective way to prevent leakage.


Reuben Saltzman, Structure Tech Home Inspections – EmailMinneapolis Home Inspections

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Original blog post on ActiveRain: Link to Blog Post