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Design Loads

Started by tframe, June 08, 2007, 12:28:48 PM

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tframe

Newbie with a few questions...

What is the best way to go about verifying live (roof) load information for my area?

Is there a rule of thumb or accepted standard for load reduction for pitch and material (example: metal roof with a 12/12 pitch)?

Thanks!

Don P

Hi Tframe, welcome,

Your local building department will have design load info. Usually there is one in the county seat at least.

No reductions, some increases are possible for unbalanced loading or drifting. I've had 3' of consolidated snow/ice build up on a 12/12 metal roof we built. If the conditions are right...

tframe

Thanks Don, and thanks for making your calculators available too...

Jordan

In vermont snow load will always control over live roof load (which is 20psf).

Don is correct that you will have several special cases for roofs. If your rafter span (horizontal distance from wall to ridge) is less than 20', you must design each side for the _ground_ snow load, which is what you'll find in the chart in the buiding code (or from your AHJ, if you're in a special region).  If longer, than there is a special formula to use.  Your balanced snow load will vary with your roof pitch and whether your surface is slippery (metal, for ex) or not (asph. shingles).  This balanced load will probably determine how big your ridge beam must be (if you are using a beam instead of a non-strucutral ridgeboard).

The official place for answers is ASCE-7, (aka SEI-7, aka ASCE 7-02 or 7-05, with the last two digits specifying the year of the code).   It's published by the American Society of Civil Engineers and is the basis for all loads on building structures. For a one-off project, I'd see if the local library has a copy...or check if you have access to a local college library - any school with civil engineering should have one.

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