Well, I have never been asked to include 25% of snow load in seismic load calcs
for less than 40 psf. I have done it anyway when I have a flatter roof with
roofing other than metal. I have also been allowed to not include it in 40 psf
areas up in the hills a little ways when the roof pitch is 6:12 and the roofing is
I would also rather see a way to include the snow load with seismic forces that
Redding used to have a 20 psf snow load until the winter of '69 when a heavy, wet
snow collapsed several large commercial roofs - If I remember correctly there were
2 Department stores and a bowling alley that suffered damaged or collapsed roofs.
I don't remember any problem with residential roofs.