Unfortunately, there is no black and white answer to your question. Much will depend on the codes adopted by the jurisdiction, and also the discretion of the local building official. However, ASCE 7, Section 7.12 states that "existing roofs shall be evaluated for increased snow loads caused by additions or alterations." Under the International Building Code, if the effect of the additional loading is 10% or less, you need not reinforce the member. Note that you want to use discretion here. If you find an existing member is overstressed by 50% without the addition, and with the addition is overstressed by 55%, you should probably still reinforce the member, to avoid being responsible for the straw that broke the camel's back. Only member receiving additional load form the new equipment, or enlarged drift footprints from the new equipment, need be evaluated.
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Ronald Hamburger, SE
Consulting Principal
Simpson Gumpertz & Heger
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Original Message:
Sent: 03-04-2025 03:26 PM
From: Sara Finlayson
Subject: ASCE 7-22 Snow Loads
If adding loads to an existing roof, do we need to evaluate the roof taking into account the new higher snow loads prescribed under ASCE 7-22 or should we use an older code with snow loads closer to what the original roof was designed for?
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Sara Finlayson P.E., M.ASCE
Sr. Structural Engineer
Gannett Fleming
Baltimore MD
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