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dith 01-26-2011 04:41 PM

Snow loads
 
I didn't see this as a topic....I apologize if someone has started this thread.

We have had snow storm after snow storm in CT this year (2011). I was wondering if someone has an idea about how much snow load the average colonial house roof can handle. If we were getting just powder, this would be a non issue. But nothing has melted and we get sleet and rain which has to increase the overall load on the roof. My best guess is that there is 16" (or more) of dense snow on the roof right now. Should I pay to get it raked off? Thanks.:(

Daniel Holzman 01-26-2011 06:27 PM

Design (code mandated) snow load has gradually increased over the last 50 years. For example, in the part of Massachusetts where I live, current design snow load for new residential construction is a live load of 38.5 pounds per square foot, which is the equivalent of about 7 inches of water on your roof. Dense snow has an equivalency of approximately 6 inches of snow per inch of water, so current design code would require that the roof support about 3 - 1/2 feet of heavy snow.

Older codes were much less strict. I recently had occasion to review plans for a house that was built in the 1950's, and the design snow load was 25 psf. Obviously I have no idea when your house was built, or what codes it was built to, but if the house is more than 20 years old it almost certainly was built to lower loading standards than are currently in place.

That is why heavy, deep accumulations of snow occasionally lead to roof failure. In your case, you may want to invest in snow removal. Alternatively, you could get up in your attic and measure the span, depth and spacing of your roof rafters, and compute how much they can support. Also check the sheathing between the joists, as it can fail under heavy load.

dith 01-26-2011 07:52 PM

snow loads continued
 
Thank you. Our house was built in 1977, and although we just had all of the shingles replaced, I am much more interested in the structure. Using the calculations you provided, at 25psf (assume worst case scenario), I should be good up to 2'+. I am talking to someone about raking the roof in the next few days. If we can make it through tonight's 8", we should be good. Thanks.

Roofmaster417 01-26-2011 11:03 PM

Quote:

Originally Posted by Daniel Holzman (Post 578582)
Design (code mandated) snow load has gradually increased over the last 50 years. For example, in the part of Massachusetts where I live, current design snow load for new residential construction is a live load of 38.5 pounds per square foot, which is the equivalent of about 7 inches of water on your roof. Dense snow has an equivalency of approximately 6 inches of snow per inch of water, so current design code would require that the roof support about 3 - 1/2 feet of heavy snow.

Thanks, I have always inquired into this matter but all my contractor friends and associates are clueless since our snow accumulations are not as intense as the north and northeast.Great info:thumbsup:

Gary in WA 01-26-2011 11:51 PM

That is sure easier than a few I had in my library; http://www.bgstructuralengineering.c...GASCE70803.htm

http://docs.google.com/viewer?a=v&q=...lpoLI0y_E8w56w

Gary


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