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October 20, 2007

The Ice Dam Cometh

If you've read Mag's article (below) about preventing ice dams and need to source de-icing cables for your situation, here's one place to start while the Canadian dollar is so good.  For more detail on electric de-icing kits, plus a step-by-step installation guide, see Canadian Home Workshop Magazine's de-icing article.
Clipped from www.amazon.com
Roof De-icing Cable 200'

Roof De-icing Cable 160'

List Price: $123.74 Price: $89.99         You Save: $33.75       (27%)    

P1020248_smallThe Ice Dam Cometh

The truth about licking icicles


If this is the time of year when you lie awake at night worrying about heat loss, you’re not alone.


Dear Mag,

I'm hoping you can help us with our problem. In August/September last year we had the old shingles taken off the roof and replaced. In March this year, we had water pouring from the soffit in the overhang, into the room behind the soffit and the adjoining room. The overhang extends about 6 feet. It was apparently an ice dam which caused this.

Before we repair the damage, I would like to know what we should be doing and will it happen again? I don't know what to do.

Mrs. P.,



Hi Mrs. P.,

Thanks for your letter. Guess what? I have the same problem at my house, where ice dams develop on our south-facing porch roof. We licked the problem with a fairly primitive solution, which I’ll get to in a minute.

First, it’s quite possible to avoid damage and leaks from ice dams. Every single roof is unique and has its own solutions, so you’ll have to use your sleuthing skills. Ice dams stem from three possible situations.

All You Can Heat

First, you may have inadequate amounts of insulation in the attic of your house, so heat is migrating from the house into the attic, and then into the roof. You can check for warm spots on your roof after the first light snow or heavy frost. Bare spots mean heat loss.

Ice dams get started on their evil path when snow melts on the warm roof, turns to water and runs down the roof to the gutters, which are usually positioned on an overhang well away from the warm roof.

The water freezes as it hits the cold edge of the roof. Even if it makes it to the frigid gutter, it never reaches the downspout. The more snow you get in a given winter, the more often this thaw, drip, freeze cycle occurs, and the more ice builds up in and around the gutters.

Once the gutters are full of ice, newly melted snow starts backing up, turning into fresh ice along the edge of the roof – hence the term ‘dam’. Additional snow-melt then has nowhere to go, and starts sneaking under shingles, eventually leaking into the house.

By the way, someone has actually patented a heated gutter system. Darn – that was one of the best ideas I had at 3 a.m. last night. But the gutters aren’t the problem; it’s the poor insulation that’s the culprit. The colder you keep your roof, the less chance there is of ice dams forming.


The Air of Your Ways

The second possible problem is that you have air leaks that are allowing warm air to get sucked into the attic. The attic itself may be well insulated, but if warm air is sneaking up there from the heated part of the house, you’ve got the same result I described in the first scenario.

You can test for air leakage by holding a lighted candle a few inches from the trap door that leads into your attic. If the smoke flows sideways and disappears into the edges of the trap door, suspect that you have an air leak problem.

Seal the trap door against drafting by installing weather-stripping, or caulking it. To further block the flow of warm air into attic or roof areas, add sealant where wires, plumbing, ceiling fixtures, chimneys and bathroom exhaust fans penetrate through the ceiling. This will keep moisture out of the attic too, which is great since condensation in the attic can ruin insulation.

Melter Skelter

The third possibility is that you have a south-facing roof with dark shingles and the winter sun actually heats the roof up enough to cause melting. This results in killer icicles and gutters that are so weighted down, they may actually pull away from the eave.

Humans have been known to attack icicles and ice dams with all imaginable projectiles, heat guns and even chainsaws. A few years ago there was a trend toward solving the ice dam problem by simply removing gutters for winter, but that ends up sending all of the late fall and early spring run-off right into the foundation. Then the basement floods. Just shoot me.

Solution Probe

The best solution is to focus on the cause of the problem. Insulate well (the best insulation for a roof is R38, which amounts to a 12-inch thick layer of fiberglass or cellulose), and block leaks that may be allowing convection of heated indoor air into attic and roof spaces. Urethane foam sealant, caulking and weather-stripping are your able comrades in this pursuit. If you have an older house with lots of hips and valleys in the roof line, or squidgy crawl spaces that make it difficult to add insulation, you may be forced into my favorite pastime: jury-rigging.

In new home construction, builders lay a course of waterproof membrane along the lower edge of roofs. This gives the homeowner extra protection from ice dams, because melted water has no way of penetrating the roof sheathing when it backs up at the gutter. You can install this membrane in 3-foot strips next time you re-roof.

Another band-aid solution is to install heated cables, both in the gutter and in a zig-zag pattern along the edge of the roof. The heated cables clip to shingles and create channels under the snow so run-off has somewhere to go. This works well at our house, but it takes monitoring throughout the winter, and you need to plug it in whenever the snow starts to melt faster than the ice. It ain’t pretty, but it’s better than a ceiling leak.





Letters to ToolGirl

I read with interest your article on Ice dams. Back in the 70's I managed a condo townhouse complex that had serious Ice dam problems. The roof was built without soffits so there was not any movement of air out of the attic. The solution was to installed soffit venting. Since installed the problem was solved.

Six years ago I bought a post and beam open concept home with cathedral ceilings. It had soffits and roof venting. Little did I know the insulation was not installed properly. I had ice down the bricks. The melt was so rapid there would be a section of roof down to the shingles with 2' of snow around it. The shingles, plywood and insulation had to be removed with foam insulation sprayed in.

Since we go to Florida for most of the winter and leave the heat at 50F or 10 C, I was concerned that under the some conditions, ice dams could occur. While the home is only 9 years old we have 7 valleys and white calcite brick. Since I still had heating cables from when the roof had a problem, I decided to keep them on. The electricity was my concern as I was not here to turn them off and on.

Then I found a heat sensor.
"EASY HEAT" has a wire sensor about 6' long that only activates the heating cables when the sensor detects water and the temperature is below 40F or 4C. When the temperature drops the water freezes so the sensor turns off. I have the cables on about 40% of the eaves, on the base of some valleys and in some down spouts, 1100 watts in all.

January 2007 our Hydro bill was 60.85 and in February 64.74. This would cover the furnace blower when it comes on and the seven 5-blade ceiling fans running at slow speed 24/7.

When the cables were disconnected our electric bill for April 07 was
$32.51 and we were still away.

Before we had the sensors, and when the cables were on 24/7, January 2002 the Hydro bill was 155.49 and in February 2002 $107.28. At that time only two fans were on 24/7.

Just thought you may find this of interest.
Brian Forrest

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