The building code sorts the ways that buildings are used into separate "occupancy classifications". Every building is given an occupancy classification when it is built, and each occupancy classification has different building code requirements that go along with it. The requirements reflect the type of hazard or uses in the building. A "change of occupancy" is when there is a change in the building's use that would place it in a different occupancy classification. Changing part of a commercial building to residential use would be a partial change of occupancy, which would typically require that the new use meet most of the current building code requirements for a new building.
If there is no legal residential use of the building already, adding or legalizing a dwelling unit triggers a requirement that the entire building be sprinklered with a full commercial (NFPA 13) automatic sprinkler system. This is expensive. Getting a sprinkler contractor's estimate may be the best first step to decide whether your project is practical.
There is generally a requirement that a one hour fire rated separation be provided between the new residential unit and the existing commercial use. That separation is most often created by applying several layers of gypsum board to the existing walls and/or ceilings between the residential and commercial uses. The separation would also have to be provided at the stairwells or any other place where the two different uses (residential and commercial) come together.
A residential use also has smoke alarm requirements.
For more information on Building Code requirements, talk to a Life Safety reviewer at (503) 823-1456. Or, visit our Development Services Center.