Zoning codes serve to control the amount of building construction in order to satisfy acceptable community standards related to residential densities and living conditions. One such requirement is the maximum number of units that can be built on a property. Density varies depending upon the residential zone in which it is located, for example, R-1 (Single Family), R-2 (Medium Density) or R-3 (High Density) and/or the property's land area.
R-1 Single Family
The R-1 zone is the basic building block of a community. The name itself, single family residential, expresses the nature to which the type of construction that is allowed, one single family house, unless the property is large enough to subdivide into more lots that satisfy the minimum area requirement of 6,000 square feet. As you further discuss the requirement with a planner, you will be advised that there may be a maximum size (floor area) of the house that is permitted which is compared to the size of the lot. This is referred to as floor area ratio.
R-2 Medium Density
For multiple family zoned properties, R-2 and R-3, density calculations vary to a degree and are based upon the lot frontage and lot area of the property. The basic rule is that the greater the lot frontage and lot area, the more number of dwelling units that could possibly be built.
For example in the R-2 zone, a lot with a frontage of 50 feet or greater and which has a lot area of 9,000 square feet, the ratio to determine the number of units is one unit per 4, 356 square feet of land area. Using an example of a 50 feet by 200 feet lot that has 10,000 square feet of land area, this lot may be developed with two units (10,000 / 4,356 = 2.3). Please note that fractions are rounded down.
R-3 High Density
In the R-3 zone, a lot with a frontage of 50 feet or greater and which has a lot are of 7,000 square feet, the ratio is one unit per 3,000 square feet of land area. Accordingly, a 10,000 square foot lot in the R-3 zone has the potential to be developed with more units.
In this case, the lot may be built with three units (10,000 / 3,000 = 3.33). Please be reminded that maximum density is potential rather than guaranteed, since other factors must be considered, including yard setbacks, desired building floor area, off-street parking and open space requirements.