Roof Live Load [IBC vs. ASCE7] 2

[yoohoooos]

Hello,

I was checking the load combinations on ASCE 7 and IBC. In IBC, the Roof Live Load is defined as "Roof live load of 20 psf or less (see below). However, in ASCE 7, it is only defined as roof live load. From my understanding from ASCE 7, Lr, could be whatever live load at the roof level. I was just wondering, per IBC definition, does that mean Lr is any live load at the roof level for 20 psf or less? What happens if we have live load of greater than 20 psf at the roof level?​

 

[JAE]

What happens if we have live load of greater than 20 psf at the roof level?

There's no Roof Live load greater than 20 psf in either the IBC or ASCE 7.

If you have a condition where you need a higher live load capacity (rooftop garden, patio, assembly area for a deck, etc.) then these no longer are "roof" live loads as defined but the roof becomes a floor and the appropriate floor live load should be applied.

 

[DanKile]

ASCE only considers live loads on the roof that are not occupancy related to be a roof live load. This is clearer in 7-16, but it is in 7-10 & 7-05. And ASCE's minimum live loads on a roof that are not occupancy related are 20psf or less. If you have a live load on the roof greater than 20psf and not occupancy related, the conservative approach would be to treat it as a live load.

 

[lexpatrie]

It's not conservative, it's how it's supposed to be treated. "roof" live load above 20 psf isn't from the roof construction/reroofing convention. They also tend to be "assembly" because there's very little middle ground in the established literature. I've had a lot of discussions with building officials on the matter in the last few years.