The snow on the north facing part of my roof has remained there for quite a while this winter causing an ice dam to form as the freeze/ thaw cycle occurs.
While I have a pretty good understanding of how these dams are formed, and that heat coils can help, I have a specific question…If I shovel off several feet of snow above the gutter when it first snows or afterwards if possible, would that help prevent the dams?
Yes, it would help avoid the cycle of melt/freeze that can build up pretty big ice dams. We have a roof rake we use for such a purpose, but we have also shoveled the roof.
Whatever you can do to alleviate the problem is far better than what can happen if you don’t. The only good that came out of our ice dams in Anchorage is that I was able to buy myself a pretty decent wet/dry vac. Then I had to pay some guys about $300 to get rid of the buildup.
This is one of those “for the knowledge base” additions:
Flashback to the day after a blizzard when my son and I spent much of the day on the roof to avoid such an outcome:
So the back roof is exactly 60’ long, and approximately 10’ across. The snow we shoveled off ranged from 1.5 to 2.5 feet deep, so we’ll call it 2.0 feet. Packed snow ranges from 5 to 25 pounds per cubic foot, but let’s be relatively conservative and call it 10. The result of all that is that we shoveled roughly six short tons of snow off the roof today.
The good part was, when we were done we just jumped off the roof.
Yup–ice dams are caused by not enough insulation in the roof to keep the surface below freezing and the insulating value of the snow itself (and the transition from warm to cold over the soffit). Anything you can do to keep the roof surface below freezing (such as exposing it to the air or adding insulation) will help. Heat tape is effective, but is really just a band-aid.
I get a LOT of snow. 25-30 feet a season. Winter lasts October to April. Shoveling would be a weekly task. Sometimes daily.
I went to a steel roof and heat cable. So far, so good.
Nitpick: the insulation doesn’t go “in the roof,” it goes against the ceiling of the living space There’s supposed to be an air gap between the roof and the insulation. From what I’ve read about ice dams (we’ve had some issues at our house in the past couple of months), there are two house modifications that can help reduce/eliminate ice dams:
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add more insulation to keep heat from escaping the living space of your house into the attic space.
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add more ventilation to the attic space so that it stays cooler, which will help keep the roof below freezing. This typically means more ridge vents and eave/soffit vents, since you need both to establish good convective flow from the eaves to the ridge. It may also mean a powered fan, although this needs some consideration for how/where to install it so that you don’t actually worsen the airflow in the attic.
Ice dams seem to happen when the ambient temp is just a little bit below freezing (which brings the temp inside a poorly-insulated/poorly-ventilated attic up above freezing) and there’s a thick layer of snow on the roof. That’s when the bottom layer of snow melts on the warm shingles, and then when that meltwater drains out into the open-air gutter, it freezes solid again. If you can’t add insulation/ventilation to the attic space right now, then the last thing you have left that you can control is the snow load on your roof that insulates your rooftop from the freezing ambient temps.
You can buy special shovels that let you remove snow from the last ~10 feet of your roof while you stand safely on the ground. I recently bought this one:
https://www.amazon.com/gp/product/B01EQ2SSL0
Haven’t used it yet, but certainly will the next time it snows. This spring I plan to look into adding insulation/ventilation to prevent future ice dams…
There’s even a wiki page for ice dams.
True, for a vented roof assembly. Roofs are becoming more and more unvented–fully foamed or a flash coat (3") plus batts. If you get to R-50 or so you keep the sheathing below freezing all winter. Mandatory for vaulted, non-truss roofs.
On reading the subject line, I was expecting a Colorado equivalent of the infamous Clark Fork ice dam. I’m disappointed it’s not.
The Channeled Scablands is a fascinating area.
How would one keep the snow out of the gutter when using a roof rake?
It doesn’t. It just changes the situation from having 2 feet of snow both in the gutter, and uproof from the gutter, to nothing uproof from the gutter, and just a little in the gutter.
The only places I have any gutter is where it gets heat cable running through it. Gutters are not necessarily a good idea. They get ripped off eventually. Ya just let it drip.
Don’t look up when leaving the house least an icicle fall and get ya in the eye.
Storm doors are a bad idea where you get a lot of snow. They open outward and can easily get blocked.
Snow slides/avalanches off of roofs have known to kill people. Seems to be more of an issue for steel roofs. When it slides WHAMMO. I have snow fences/slide stoppers on my roofs. There are a number of different designs.
That picture appears to be a shake shingle roof. A BIG no no. Might be attractive, but a huge fire hazzard. I’m not sure if code allows them around here.
It’s a strange relationship. You want the snow off of the roof, but not all at once.
This. It seems like the smart way to go. I was always amazed at how cobbled together roofs were no matter where one lived. Overlapping shingles, shake shingles, and so on.
In New Mexico, you see a fair amount of rounded half tiles stacked on each other. Pretty, but you wonder how that woks out in big winds. The adobes tend to be flat roods covered by tar or something similar.
T the last decade I see a lot of people going to steel roofs, which makes a lot more sense. Combine that w/ a steeper roof pitch and the heat cable, that would appear to be the best solution.
Yeah, seems to work. But, note, if you need to get on the roof, there is not enough traction to do it. I installed a Starlink dish, and could not get traction on it to do it on a 6-12 roof.
When it was asphalt shingles, I would just walk right up. On the steel roof, I had to use ropes, a climbing harness and ascenders. Had to throw the rope completely over the house and secure it. I had to start with a small rope (climbing rope was way to heavy to throw that far) and then drag the climbing rope over with the smaller rope. It was quite ridiculous.
It is quite impressive that you approached the project with such rigger.
My house came with an ice rake. Ice dams aren’t a big issue with this kind of roof though. I think the previous owners ran into common snow build-up problems. Poorly designed soffits can cause ice dams by allowing snow and ice melt over the roof to refreeze over the eave.
It was quite a rig David. Luckily I have climbing experience and had most of the gear. I’m 62 years old though, so would prefer to not do it again. I had to set up a way to keep a simple bag of tools from sliding of the roof.