The size of the building or addition depends on the zoning district in which it is located. Each zoning district restricts the size of a building by establishing separate setbacks and lot coverage (footprint of building and accessory structures) requirements. In single-family and two-family residential districts (R1, R2 and R3) buildings must also comply with impermeable surface and Floor Area Ratio (F.A.R.) requirements.
In residential districts, only a limited amount of the lot may be covered with materials that do not allow water to be absorbed by the ground (buildings, patios, sidewalks, etc.) The impermeable surface requirement varies by zoning district. The F.A.R. requirement states that the maximum floor area of an existing or proposed building cannot exceed 60 percent of the lot area. The F.A.R. is a ratio of the area of a building to the area of a lot.
As the regulations effecting building size very by zoning district and some restrictions such as impermeable surface and F.A.R. require extensive calculations, it is best to contact Building, Zoning & Property Standards Division of the Community Development Department at 847/933-8223 before planning your project.