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Research report2024San Diego

Not So Gentle Density: An Early Assessment of the San Diego Bonus ADU Program

California ADU researchers

Main finding

The bonus program enabled small multifamily-style infill, but utility costs, financing, geography, and implementation capacity constrained early delivery.

40% of proposed bonus ADUs were in Moderate Resource areas, versus 25% of all ADUs

Most important limitation

Most observations were proposed or permitted rather than completed; overlapping state and local reforms prevent a citywide causal conclusion.

From the publication

Inspect the authors' figure directly

Figure from the paper

Figure 6 · Proposed bonus-ADU projects by units per project

Most proposals remained modest, while a smaller group used the program for substantially larger infill projects.

Published histogram of proposed San Diego bonus ADU projects by units per project, excluding one 148-unit outlier.

Source: California ADU researchers (2024), Figure 6; PDF p. 31.

Read carefully: The records are proposed projects, not completed homes; the source excludes one 148-unit outlier from this chart.

How this study is used

Claims this evidence supports

Strong evidenceLegal on paper is not the same as buildable in practice.See the full evidence stack →

Policy connection

Solution guides informed by this study

01Make room for apartments, shops, and neighbors02Bring back the homes between a house and a high-rise03Let homeowners add a home04Stop forcing every home to buy parking06Set clear rules—and say yes on time

Reference

California ADU researchers (2024). “Not So Gentle Density: An Early Assessment of the San Diego Bonus ADU Program.”

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