rain-on-snow surcharge on tanks
 

rain-on-snow surcharge on tanks
i would like to get feedback on asce's requirement for rain-on-snow surcharge loads on tanks, say tall silo tanks. is this required? section 7.10 of asce 7-05 states that, "for locations where pg is 20 psf or less, but not zero, all roofs with slopes (in deg) less than w/50 with w in feet shall have a 5 psf rain-on-snow surcharge." w is the horiz dist from eave to ridge in feet.
my pg is 14.5 psf, and my tank is 20 feet in diameter with a slope of 13 degrees, from eave and meeting at the center of the roof tank. my w/50 would be 10/50 = 0.2 degree. my tank roof slope is 13 degree. according to asce, i do not need the rain-on-snow surcharge, is that right?
thank you so much for your advice and feedback.