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How do I remove snow from my roof? How about 4" of snow covered with 1/2" of ice? How do I know when I should risk getting out there to try to remove it?

We just received a notice from The New York City Office of Emergency Management saying:

The Dept. of Buildings is reminding property owners to de-ice public areas and safely
remove snow from roofs, overhangs, and awnings. The buildup of wet snow and rain can 
present a threat to the structural integrity of a building.

I live in a suburb of NJ, but presumably the message still holds.

I have been out on my back roof (accessible from my bedroom window) in the rain but the ice-covered snow that we've had build up lately is another matter. I don't want my husband out there either. He is concerned for the structural integrity of the roofs, and now I get that, but it's not worth risking life and limb. Any suggestions would be super. Thanks!

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4" of snow with 1/2" of ice shouldn't be a problem for a roof in good structural condition. I worry when our roof in CT gets more than 30" of accumulation. –  TomG Feb 14 at 2:54
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5 Answers

up vote 5 down vote accepted

I would suggest a roof rake - like this. You would start about 3-4 feet up, crack through ice and then rake down. If you have a tall roof this becomes a safety issue and might need two people - one to secure ladder. It isn't easy work.

Also if you can safely get on top of the roof it is much easier to push the snow off.

enter image description here

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looks like what we'll have to do. today there's no getting out to a hardware store for one anyway, even if there were any at our local stores. –  kewpiedoll99 Feb 13 at 17:40
    
Looks like your linked NT item is no longer available, may want to update it –  JohnB Mar 14 at 17:49
    
Thanks @JohnB. Guess the extra pub made NT sell-out. Will try a Menard's link since more people have these local in US. These aren't fancy though. –  DMoore Mar 14 at 18:05
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The NYCOEM has no authority over NJ. I'm guessing you received the notice as part of an alert system you signed up form. Mailing list, twitter feed, etc.

The reason it's important for people in NYC to clear their roofs is because roofs generally are right over the sidewalks. You don't want melting snow dripping on the walks and freezing or worse, having chunks of ice or snow falling 6 stories down on people.

I live in NJ just outside Manhattan and I have never seen anyone rake snow off their roofs. Generally houses are set back from the sidewalk, at least 50' in my area. If your home is like most, you have regular landscaping just under your roof and not a sidewalk. If you do have sidewalk under the end of your roof, or have some other issue like maybe a really old roof in bad shape that can't handle the snow load, I don't see a reason to bother with it. I just knock the icicles off were the front and side walkways are and throw some ice melt down on the front walk so it doesn't freeze for the mailman.

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99% of the time there is (or should be) no need to remove snow from a roof that is properly built for the area it is in. "Properly built for the area it is in" should include the ability to hold up the expected maximum snow load for that area until it melts. As a side note, in new construction, it is often VERY affordable to add 10-20 pounds per square foot of loading to the "code minimum" for the area when buying the trusses. As far as I recall a paid about 4% more for a 20% increase (and peace of mind) on my last building project.

Only shoddily constructed buildings require removing snow from the roof, with the associated labor and fall hazards, excepting the already mentioned city condition of ice falling to sidewalks (and that is arguably also bad design, as clambering around on icy roofs is not any safer in the city, especially if its 6 stories to a cement sidewalk...)

A handy and practial link from Sterling Mass with a very direct method (core it, melt it with a coffee can, measure the depth of water in the can used to core it, and multiply by 5.2 lbs/sqft/inch of water depth) to assess the current weight on the roof (since snow varies a lot.) So if your 4.5 inches was solid ice, it would only weigh 23.4 lbs/sqft, well below any standard US roof (minimum 30 PSF per uniform codes even where no snow is expected)

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I saw a roof rake on This Old House about a year ago that looked so simple, yet brilliant. Instead of having to scrape a little bit of snow at a time down to you or to push, this device slid a sheet of plastic between the roof and the snow so that one big column came down at one time. I don't have the need for one but it looked like a real time saver.

enter image description here

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Saw this. They are selling out with the old tripartite Polar Vortex this winter. –  kewpiedoll99 Feb 21 at 2:08
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Besides the amount of snow on your roof, an important consideration is the slope of the roof.

If the roof is barely sloped (level or nearly level), ice and snow accumulation is more of a priority to do. Naturally it is also safer to do.

If it is moderately sloped, 20°–35°, then it is less urgent to clear as it will naturally shed excess load under many weather conditions. Snow covered with ice is one of the situations in which it probably will not automatically shed excess accumulation. Unless you happen to have little insulation in the ceiling/attic. In that case, you could simply turn the heat way up inside the house (90+ °F) for a few hours and let the heat do the work safely and easily. As someone else pointed out, you need not bother if there is nothing endangered by falling ice.

If the roof is steeply sloped (35+°), you should not need to do anything: it should just slide off. That is why buildings in deep snow areas, like Alpine lodges, have steep roofs. If you have to get out on it when it is snow covered, hopefully you already have climbing anchors installed.

If the roof is structurally challenged (which is unlikely), it might already be too late to do anything about it. If it is a two or more story building, remove non-replaceable items from the attic and top floor and stay on the lower floors until the danger is passed. If there is only one floor, maybe stay at somebody's else house or a hotel for a day or two.

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