The weather has been tough in the Northeast and New England this winter. Earlier this season, a lake-effect storm dumped over 5 feet of snow on Buffalo. Boston is bracing for a Valentine’s Day blizzard that could bring more than a foot of snow to a region that’s already seen 3 major storms leave up to 6 feet of snow over the course of a month. With plenty of snow already on the ground and more on the way, should homeowners start worrying and shovel off their decks?
Probably not, says Boston deck builder Jim Finlay. “Don’t worry until the snow is above your rails. If you can see the rail tops, you’re OK—even with some rain,” Finlay writes in a popular blog posted on his website. Decks are required by code to support their own weight, plus at least 40 pounds per square foot (psf) in additional loads – from people, pets, furniture, and snow and ice. Many builders, including Finlay, build to a higher standard, and frame their decks to support at least 60 psf—more than the design snow load for roofs in most states (you can find the ground snow load in your area by viewing this interactive ASCE-7 snow load map.
The weight of three feet of snow can vary a lot, depending on how wet the snow is. The so-called "design weight" used by engineers is 69 psf, while the actual weight is estimated to range between 36 to 54 psf ... hence Finlay’s recommendation to start worrying once the snow starts drifting over the top of your 36-inch-tall railings.
As snow accumulates, of course, it gets denser. Add warming temperatures or rain to the equation and things get sketchy, even for a deck built to code (and there are a lot of decks that aren’t built to code). But if there’s as much snow on your roof as on your deck, you should be more worried about your roof.