One of the first steps in any building project is evaluation of the appropriate occupancy group. This drives building size, building height, construction type, exiting and fire separations.
Residential Group R is the occupancy group used for buildings that include sleeping rooms and are not insititutional and are not generally regulated by the Interntaionl Residential Code. The IRC typically regulates single family homes and duplexes, any structure with more than two units is in the IBC. There are four different occupancy groups within R.
The first occupancy group is R-1. This group is for transient uses like hotels, motels and boarding houses.
The next group is R-2. R-2 is the group we see most often and it for residences where occupants are primarily permanent. This includes apartments, dormitories, fraternities and sororities. It also includes vacation timeshares (again with more than two units) and convents and monasteries. Congregate living facilites with 16 or fewer occupants go into group R-3.
R-3 is something of a catchall group for permanent occupancies that aren’t R-1, R-2, R-4 or I. These include buildings that are in the IBC but have no more than two units. Adult facilities and child care facilities that provide accomodation for five or less people less than 24 hours a day are R-3. Where these facilities are in a single family home they must comply with the IRC.
R-4 is for residential care/assisted living facilities including more than five and not more than 16 occupants. Generally it is very similar to R-3’s requirements.