Title 24 Requirements for Mixed-Use Buildings
A mixed-use building is assessed under two different sets of standards at the same time — the multifamily requirements for the dwelling units and the nonresidential requirements for everything else. Which multifamily set applies depends on the habitable-storey count.
Two rule sets in one building
The residential portion is assessed under the multifamily standards and the commercial portion under the nonresidential ones. They are not variants of each other — different requirements, different compliance documents and different verification regimes apply to parts of the same structure.
That is the defining difficulty of mixed-use, and it is a documentation problem as much as a design one.
The habitable-storey count decides the residential family
Up to three habitable storeys, the dwelling units are low-rise multifamily and use the LMCC family. At four or more habitable storeys above grade they are high-rise multifamily and use the nonresidential NRCC set instead — the same family as the commercial ground floor.
A habitable storey has at least half its volume above grade, so a partly buried podium or parking level can move a building across that line. On a mixed-use scheme that is often the single most consequential definition in the project.
The ground floor is genuinely commercial
Retail, restaurant or office space at street level is assessed as that occupancy: lighting power by function area, occupant sensing where required, mechanical requirements including the economizer threshold, and acceptance testing on lighting controls and mechanical systems. A restaurant tenancy brings the kitchen exhaust requirements with it.
Shared and common areas
Lobbies, corridors, parking and plant serve both halves of the building, and which set of requirements they fall under follows from how they are classified rather than from who uses them. Corridors and parking areas are named for occupant sensing in the nonresidential set.
What to settle before design
The habitable-storey count, the boundary between residential and commercial portions, and how the shared areas are classified. Those three answers determine which standards, which forms and which testing apply — and all three are cheaper to establish on a drawing than after a plan check comment.