How the BLI converts net densities to gross capacity: streets, open space and redevelopment

At the July 16 Etech meeting, planning staff described the arithmetic behind translating historical (net) densities into the gross density factors used to estimate future housing capacity. "After the buildable acres are calculated, the BLI gross density factor is determined. This density factor is the number of dwelling units per buildable acre," Thea Evans explained, adding that the factor is based on land-use designation, pseudo-lot size, slope and elevation.

Staff said the conversion from net to gross must subtract land taken for streets, protected areas, and other non-buildable dedications. Heather (speaker 1) noted they examined monitoring data from previous subdivisions and used historical averages to estimate street dedications (for example, small lots often require no additional dedication while 1'5-acre sites showed about 8% dedication in past data, with larger sites sometimes needing ~10%). Beth Goodman said a combined safe-harbor (rights-of-way, parks, schools) exists at roughly 25%, but there is no single safe harbor for rights-of-way alone. "That safe harbor that exists would be a safe harbor for rights of way, for parkland, and for schools all put together... assuming 25% of land would be used for those things," Goodman said.

Staff said they are updating monitoring inputs through 2025 before finalizing the net-to-gross conversion factors and that interim percentages were borrowed from the 2021 monitoring run to keep the analysis moving while they update application-level data.