Roof Live Load and Attic live load

[SHBhuiyan]

Hello all,
I have a question regarding the roof live load and the Attic live load without the storage.
The IRC recommends a min roof live load of 15 psf (smaller than 4:12 pitch) and min attic live load without the storage is 10 psf.
So, do I need to add them to find the total roof live load for designing the wall or foundation below for residential projects. Thank you for your time.

Regards,
Sbhuiyan

SBhuiyan
Structural Engineer

 

[lexpatrie]

Roof live load (Lr) is on the rafters, it's like construction loads/during re-roofing, people on the roof, and I suppose a bit of a contingency for the 300 lb firefighter plus gear, the (storage) live load (L) in the attic is on the ceiling joists, generally the two do combine, but conventional allowable stress design would put a 0.75 factor on both when they are combined for a foundation design. (Generally the foundation allowable bearing would also be in allowable stress).

Highest load case controls, this isn't all the load cases, but:

Dead
Dead + Live
Dead + roof live or snow
Dead + 0.75(roof live or snow + live).