roof live load reduction

huangyhg

roof live load reduction
when should the roof live load be non reducible?  it is reducible per ibc 2003 and 2006 for structural elements  with tributary area over 200 sf.  i see no reference to when a structures roof live load should not be reducible if the tributary area is over 200 sf.
thanks for any help.
find a job or post a job opening
i think there is a limit of live load above which you are not allowed to reduce live load effect.  it is probably 80 psf?
you cannot reduce live loads of 100 psf or greater.
technically a live load, although the code might term and deal with it separately, snow loads should not be able to be reduced either since since the load is uniform when it falls - it falls on the whole roof, not just part of it, and probably drifts too.  hence no supported area reduction for structural framing   
mike-
i would always consider snow as a roof load regardless of whether it is a deck or whatever else it may be.  roof loads are not reducible per code, correct?
in general, yes.  however, a waterproof deck is technically a "roof" over the unit below.  technically, at 40 psf ll, that is area reduceable, although the structural   
the building codes allow for a roof live load reduction for tributary area and roof slope.  the equation in the ibc is lr=lor1r2.  r1 is for tributary area above 200 sq. ft.  r2 is a reduction factor for roof slope above 4:12.  snow load is different than roof live load.  i live in a municipality that does not allow any roof live load reduction.  20 psf no matter the tributary area or roof slope.
i agree with archeng59 per ibc snow load is reducible and live load is not.
fasboater,
i think archeng59 is saying that roof live load can be reduced.
my mistake, i was thinking general live load not roof live load. roof live load lr is reducible.
professionally, i would never reduce a roof snow load for my above reasons stated, even if it is allowable.
mike mccann
mccann engineering
steel deck roofs are non-reducible.