The Ice Dam Cometh
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The 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., Mississauga
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.
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
Posted by: Letters to ToolGirl | 29/10/2007 at 06:32 PM