Does anyone know when the requirement started for the common walls and ceiling of a garage to be sheetrocked? The first reference I could find was 2006. The house I inspected was older than that and not being sure, I recommended they install the sheetrock.
A recommendation for enhanced safety is sufficient.
I believe fire separation walls have been required as far back as the 1930’s.
UBC 503.a 1927 required 1 hour fire rated material at the wall adjoining the dwelling.
In my opinion all garages should be drywalled and if it hasn’t it should be explained to your clients that it is something that they should consider. They can check the code your location follows for the requirements. Some areas 5/8 Type X is required while other allow 1/2". A self closing/latching 20 min rated door with a seal is also recommended. Joints should be tapped, fire rated foam should be used to seal around the door and larger openings and fire caulk for smaller gaps. It has been found that air movement was more important that drywall thickness and that 1/4" hole in the drywall can be enough to let fire into the structure on the other side causing major damage. Plus it makes for a nice garage.