Tips & Tricks | Structural Engineering (5)

August 24, 2026

LL vs. LLS in RISA: What's the Difference?

When defining loads in RISA, you’ll see two live load categories: LL and LLS. Both are live loads, but the preset load combinations incorporate them differently. Understanding this difference helps you assign loads correctly and get accurate results. Quick Definitions: LL = Live Load typical live load that qualifies for lower load factor in code 0.5 factor applied in applicable LRFD load combinations from ASCE 7 Standard factor applied in applicable load combinations from NBC LLS = Live Load Special higher or special use live load that does not qualify for lower load factor such as loading over 100psf, garages, and assembly areas. 1.0 factor applied in applicable LRFD load combinations from ASCE 7 Increased load factor applied in applicable NBC load combinations Why There are Two Live Load Categories The two categories exist to incorporate the different load factors required for the live load as prescribed in both ASCE 7 and NBC. In ASCE 7, an exception is allowed for the load factor applied to the live load in strength design (LRFD) load combinations. “The load factor on L in combinations 3a and 4a is permitted to equal 0.5 for all occupancies in which L0 in Chapter 4, Table…