Towns follow county policy and procedures regarding planned development initiatives. These guidelines regulate the allowable density or occupancy for a specific site. The requirements for development density vary by county. For example, in Renton, Wash., measures for determining and calculating these conditions are published to advise potential developers of items such as right-of-way improvements, drainage basins, wetlands, slopes, potential landslide areas or hazardous material deposits.
Determine the base density. Go to the county office and ask for the planned urban development for the designated area and read the information regarding the dwelling unit per acre information, which is determined by the zoning designation for the lot.
Assess the net buildable area. From the determined site area deduct the areas within a project site that are required to be dedicated for public right-of-way, critical buffer, storm water control, on-site recreation, regional utility and other required setbacks.
Calculate the minimum density adjustments for moderate slopes. Multiply the square footage based on the designated slope increment by the designated median slope value as provided in the minimum density adjustments table for residential developments.
Derive the residential development density. Multiply the base density in dwelling units per acres by the net buildable area in acres by the derived minimum density percentage to determine how many homes you can build.