I have a problem that occurs each winter. I get ice on my roof. This
does not appear to be damaging the roof or causing leaks. My main
concern is that when a thaw occurs, the ice comes thundering down and
could be very dangerous if it hit somebody. I am looking for
recommendations as to how to either keep the ice from forming or keep
the ice from falling.
Our roof is rather unique. We have a flat roof (gravel topped) that
has has a peaked shingled roof built on top of it. There is a dormer
built into the south facing side of the roof, which contains a window
that provides ventilation between the two roofs.
Two things combine to cause ice formation on roofs:
1. heat loss
2. inadequate ventilation
The window may not be enough ventilation for your roof. Ideally, you
would want ridge and soffit vents to allow the air to flow up the
inside of the roof surface. You may also want to look at how much
insulation you have in your ceiling and see if you can improve that as
A short term fix could be to add heating wires along the first couple
of feet of roof near the bottom and plug in the heaters whenever you
see ice building up to dangerous levels. It's a little wasteful, but
maybe less expensive in the short term and I've seen people use this
method effectively to prevent ice-dams from forming and backing water
up on the roof.
I just had an roof constractor give me a multi-thousand dollar estimate
for installing heating cables along the edges of the roof (about 300').
Then I looked online and saw DIY heating cables selling for about
$1/foot. This seems to be a big price difference. Where is the extra
cost (10x) coming from? Is there a significant difference between a
DIY kit and the equipment a "professional" would install? Is it all
labour? Or am I being taken for a ride?
What exactly is being quoted by the contractor? Are they
thermostatically controlled or timed somehow? Is the contractor wiring
the cables directly to a junction box somewhere? I think the DIY set
is only on when you plug it in and just has a dangling cord that you
will need to run an extension cord to. Also, about 300' of cable can
be worth at least a day of labor for installation if the contractor
takes their time. Plus the contractor needs to make a profit from this
so there's a markup on parts most likely. Take a look at the
contractor's proposal closely and compare with the DIY kits to see if
you're comparing apples-apples.
Louie has some good advice.
Personally for this winter, I would go for a bunch of soffit vents and
gable vents if you can. Gable vents because they have to be quicker
than a ridge vent (which would work better).
Check out your ceiling insulation as Louie said and the vapour
There should be no way for warm room air to leak into the attic.
Last house I had got ice dams on a roof with a low slope. Cables
were already installed on the roof so we decided to use them.
They had to be powered ON before the dam formed to work well. Uses
It would have been better to fix the cause instead of the symptom.
I dsicussed soffits with the contractor. He said to do that would be
such a large estimate that he didn't even want to consider it. It
would involve ripping out all our existing soffits (wood, unvented) and
replacing them. Add to that any complications due to the fact that the
interior may require work to accomodate ventilated soffits (given the
unique, double roof, construction of the roof).
One thing I am wondering though. The peaked roof over our flat roof
has a dormer in it, with a window that is currently closed. Perhaps I
can solve this problem just be opening the window?
I got this done a few years ago by an electrician, not a roofing contractor.
I needed about 120 feet of heating cable on the roof, plus 30 feet in the
gutters, plus a cable conduit to the breaker panel. If I remember correctly,
it cost around $600. Took one guy about 4 hours to do. So, about $150 for
the heating cables, and $450 for the remaining hardware and labour. Call an
electrician instead of a roofing contractor, maybe you'll get a better
An old roofer once told me he won't climb a ladder for less than $350
because he learned that's what it costs to offset the risks involved. So
start with a base charge of $350 per man per day then add hourly labor
and materials plus overhead for both. It can shoot past $2K pretty
easily. That said, you can probably get a lower price from the folks
south of the border who find their way into the trades up here.
I just spoke to another roofing contractor, and he suggested yet
another solution: install "ice aprons" (essentially flashing) along the
edge of the roof. His claim is that the ice cannot hold on the apron,
so ice building is not a problem.
Does this make sense? I noticed one of the churches in our
neighbourhood has the same solution, except that they applied ice
aprons *and* ice railings.
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