Designed Roof Load for Flat Roofs

Old 01-16-11, 09:57 AM
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Unhappy Designed Roof Load for Flat Roofs

Using the calculations for a standard roof load in the northeast of 40 lbs per sq ft. 1.25 lbs for sq ft snow for each 1" of snow. I have 24 " snow on a 2000 sq ft.... 20 degree pitched roof. That would give me 60,000 lbs of snow weight up there.

What is the roof load calculation for flat roofing. I have a extended flat rubberized roof of 700 sq ft. There is also 24 inches of snow up there.

Looks like a little roof shoveling today
Old 01-22-11, 11:58 AM
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Im also interested in the formula for a flat rubberized roof. I have an extension to my home that is just shy of 2500 sq feet! I dont want to do damage to the roof so if shoveling is not required it may be for the better.

Anybody have this formula?
Old 02-10-11, 07:51 PM
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In order to determine what snow load is on your roof, take a fish scale and a plastic bucket, measure a 12" x 12" area, cut with a show shovel, and then carefully shovel everything within that perimeter (including ice and water) into the bucket and weigh. That will give you the actual load in pounds per square foot. Code formulas are not helpful, because they make assumptions about snow density that do not include ice buildup and melting snow (or worse, rain on top of snow). Just see what is happening in Connecticut right now--the codes have not anticipated current snow patterns.

Once you know the load, you can use tables to figure out the capacity of your roof. Compare capacity with the load (making sure your units are consistent--usually pounds per square foot).

In general, if your measured snow load (using the fish scale and bucket) is more than the code snow load in your area, you probably should start shoveling.
Old 02-11-11, 05:59 AM
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Once you have a significant buildup, the actual weight is less important, although I like eclarks method. The problem is, what is up there will act like a huge sponge and if we get rain before a whole lot of melting, that weight load will literally go through the roof. Even if we get a lot of warm weather, the snow simply settles and very little actually melts off. You have to get that sponge off the roof, but be careful.


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