Reuben's Home Inspection Blog


Preventing Ice Dams From The Exterior


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


Comment balloon 16 commentsReuben Saltzman • January 04 2011 06:11AM


Tis the season for ice dams. Amazing how many homeowners let this ruin there eves. Good post for fixes Reuben.

Posted by Randy Ostrander, Real Estate Broker, Serving Big Rapids and West Central MI (Lake and Lodge Realty LLC ) over 8 years ago

Uggghh, ice dams, read both you posts, some good info on those hateful and damaging ice dams. So important to have the house built properly the firs time that is why we need good inspectors like you to forwarn buyers.

Posted by David Popoff, Realtor®,SRS, Green ~ Fairfield County, Ct (DMK Real Estate ) over 8 years ago

Thanks for reading Randy.  A lot of homeowners don't realize what this will do to their house.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

David - I agree, it really helps to do it right the first time.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

Reuben, great information.  I was showing some vacant property in Angus, a town about 15 minutes north of me, and saw some major ice damming... you could see the damage it was causing.

Posted by Chris Smith, South Simcoe, Caledon, King, Orangeville Real Esta (Re/Max Chay Realty Inc., Brokerage) over 8 years ago


This is a helpful series. Ice damming is a real problem and it can certainly cause some damage.


Posted by Brian Madigan, LL.B., Broker (RE/MAX West Realty Inc., Brokerage (Toronto)) over 8 years ago

I had a client call me about those cables.  Do they work?

Looks to me as if you rake or shovel enough snow from a roof you can just jump down when done!  Easy, soft landing!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 8 years ago

Chris - I've seen a ridiculous amount of damage to homes these past few weeks.  It's crazy.

Brian - thanks.

Jay - yes, de-icing cable work very well at preventing leakage from ice dams. Also, you're right about shoveling off so much snow that I makes for a soft landing; by the time I was done pulling all the snow off my own roof, I ended up with a snow pile that was about 3' below my soffit!

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

I'm noticing a theme here. If I didn't know better I'd say it's very cold and snows a lot in Minnesota. What do the de-icing cables cost to run? Resistance heating is never cheap.

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) over 8 years ago

James - howdja guess?  This has been a really bad year for ice dams in Minnesota.  The traffic on my web site is up by about 300%, and it's all people looking for ice dam solutions (thanks Google Analytics).  

The cheap de-icing cables use 5 watts per foot, and the expensive ones use 8 watts per foot (two 60 ft cables @ 5 watts = 600 watts).  It ain't cheap, but it's better than having water leaking in to the home.  

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

Hi Reiben, it's always interesting to see what you post.

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'll be re-bloging this one. Thanks.

Posted by Robert Butler, Montreal Home Inspector | Aspect Inspection (Aspect Inspection) over 8 years ago

I know about those snow brows - there's one particular house that I drive by every day, and I always wonder how the heck it's still there, seeming to defy gravity.  I bet those snow brows do an excellent job of hiding ice dams.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

That's exactly what they do, incubate and hide ice dams. The snow functions as insulation so a thick blanket of it will keep the shingle surface warm (and melting) as long as there is heat loss from below. As you know removing the snow is removing the insulation, so heat loss dissipates rapidly without melting anything.

Thanks, Reuben

Posted by Robert Butler, Montreal Home Inspector | Aspect Inspection (Aspect Inspection) over 8 years ago

Reuben, very interesting thanks for the post. Im gonna put up some Ice dam pics from this past snow storm in Jersey

Posted by Wilbur Lloyd (AR Home Inspection Service of New Jersey) over 8 years ago

Thanks, Reuben - I am looking at my ice dams right now and thought this would be a great reblog.  We are having a huge problem out here in CT.  Thanks for the information.

Posted by Peggy Chirico, REALTOR® 860-748-8900, Hartford & Tolland County Real Estate (Prudential CT Realty) over 8 years ago

Robert - that's exactly it; most people don't equate snow to insulation

Wilbur - I heard you guys got dumped on.

Peggy - I hope it helps!

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago