what's the best way to protect a flat roof from heavy snow?

Question

On the NE here and have multiple properties with flat roofs.  Could be up to 2ft of wet snow.  Any suggestions to prevent roof failure or leaks?

Matthew Paul · Answer

Have a good insurance policy .

Account Closed · Answer

@Brandt Tingen, a properly designed and constructed flat is no more apt to fail than a pitched roof, so simply building a pitched roof isn't the solution in my opinion.  And even pitched roofs can hold sticky snow.

Given the impending snow storm which I presume prompted your post, building multiple pitched roofs in the next 24 hours or so is unlikely.

As to your request for suggestions... if you're truly concerned with failure (i.e., collapse) I suggest you relocate the occupants ahead of time.  As for leaks, the weight of a heavy, wet snow makes things move and may create compromised points... where a leak might happen is a WAG so it's a little tough to predict.

Right along with wet, heavy snows are power failures, so heating cables may be moot. And if they melt snow which then turns to ice, this could add to the problems.

Whatever you do, don't climb on the roof to shovel - your added weight and movements, along with unequal loading as you slowly clear, may invite disaster.

Shelley F. · Answer

One thing I love about reading posts is adding new words to my vocabulary. I had to think for a bit about 'WAG' but I think I got it!

Aaron McGinnis · Answer

Build a pitched roof over it.

Jeremy Tillotson · Answer

@Brandt Tingenfrom a long term perspective any chance you can build a pitched roof over? I have also seen heating cables to melt the snow and the cable goes some ways into the drain so it doesn't freeze. To make a immediate difference one could have it shoveled off.

Brandt Tingen · Answer

Account Closed Thanks for the thoughtful reply.  Yes building pitched roofs before the snow starts to fall has about a negative 100% chance of happening.  I can lean an extendable ladder on the face as it's a masonry building, put a few sandbags at the base of the ladder, and use an extendable snow rake to get a few inches off... perhaps.  I talked to my inspector and he said if it's been there for 75+ years it's probably seen worse, but they are predicting this could be a 100 year snowstorm.  I do not think however there is a real danger of collapse this is from a time when things were overbuilt I think they are 2x12 roof joists back when dimensional lumber was actually the quoted size and everything was hand nailed.  There is a skylight so I may get leaks around that and if the snow climbs above the parapets then maybe the flashing there will fail.  I guess it's a wait and see thing.  Good thing is that the duplex I am worried about most both tenants keep their thermostats at 90 degrees in the winter (thank god electricity and gas are separately metered) so my hope is that the high heat in the interior of the home travels the thermal bridge of the roof joists and aids in the melting of the snow on the roof... may be wishful thinking.  There is a 1:12 or 2:12 pitch on this roof so it's not like it is literally flat.

Account Closed · Answer

2 suggestions that I've seen from This Old House:

• Avalanche roof rake https://youtu.be/eacQwzoEztA. If you have a basement, I'd highly recommend removing these snow piles from around the house. Otherwise, significant moisture will be residing around your basement walls for prolonged periods. 
• Roof heat tapes several feet up from the gutters. Pic at this link. Not a perfect fix, but less labor intensive. Just make sure you whatever electrical source you use doesn't have water penetration risks and preferably GFI compliant. If you DIY with extension cords, use electrical tape to seal off water as much as possible.

Hope that helps.

Joe Splitrock · Answer

In general most roofs will not collapse due to snow, but every roof has a limit. The nice thing with a pitched roof is I can use my roof rake to remove snow from the ground. I am not sure if a roof rake works on a flat roof. It probably depends on access angle. There are many documented cases of roofs collapsing under extreme snow weight. Removing snow is common in my part of the country, but usually it is done to prevent ice dams.

Mark Holencik · Answer

Your chances of having any problems are slim to none. As soon as the snowing is done it will start melting as the tempertures will rise to in the 40's on Wednesday.

We usually do not start shoveling roofs on the first snow fall.

People that do not take care of their roofs blame the flat roof for the problems. People that tell you to get rid of the flat roof have no knowledge of roofing.

Dennis Griffith · Answer

@Brandt Tingen

I have a flat roof over my garage, with which I have always had leaks when there was a moderate to heavy snow fall.  About two years ago, I had a rubber membrane surface installed over the original roof and have had no leaks since then.  I live in Charlotte, NC and could find no one who installed the rubber membrane roofs.  I was connected to an installer from Detroit who had done dozens of them over the years.  I was fortunate enough to get him to come down and do the job for a reasonable price.  I can certainly vouch for the roof as it relates to leaks, so that is something you can possibly look into going forward as a long term solution.  As far as roof failure is concerned, if two feet of snow accumulates on your roof, all bets might be off.

what's the best way to protect a flat roof from heavy snow?

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