huangyhg

unbalanced snow load ibc 2000
i am designing roof rafters for a single family residence. if i apply an unbalanced snow load, the rafters in the ibc residential code tables do not work. (my model includes a ceiling joist). i can only get the rafters in the table to work with balanced snow loads.
does anybody know of a stipulation in the code where you do not have to apply unbalanced snow loads to residential buildings?
thanks!
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so why dont you design with an unbalanced snow load.
i don't want to design the roof for unbalanced snow load if i don't have to. i was already accused by another engineer of being overconservative with the roof design on a previous residential design project. i would like to know definatively either way.
the leeward drifts from the asce 7 hammer a rafter design with 150% pf. as i understand it, this is what the ibc says to do irrespective of occupany (i=1.0).
you are governed by the irc. the ibc is a code book whereas i view the irc as more of a recipe book. i am doing good to stay up with the ibc changes every three years and thus do not profess to know that much about the irc. look in the irc and i expect it says the span tables are ok w/o drifting. irc r301.2.3.
for what it's worth, i design any rafter and its connections for the drifted snow condition.
check whether ibc and asce 7 even govern this design. usually, the irc controls residential design and you may not have to even refer to the other two.
if it is single family with 3 stories or less, then irc is your code. if your ground snow load is 70 psf or less, you use the tables in irc (chap 5,6 and 8). i don't have the commentary handy, but i think your issue is taken into account in the table values.
zcp

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