SB 1211 for 24-unit apartment in San Mateo
A 24-unit 24-unit apartment in San Mateo qualifies for up to 14 new homes under SB 1211 — 8 detached ADUs and 6 interior conversions. At San Mateo's median rent of $3,000/mo, that's ~$504K in additional gross annual rent.
The San Mateo scenario
The scenario most San Mateo 24-unit apartment owners face: an existing building, mature trees, and a back lot that's currently doing nothing. SB 1211's 4-ft setback and 18-ft height envelope fits 8 detached units behind that primary structure with room for fire-access in front.
Local tip for San Mateo: Peninsula tech rents; very strong upside.
Large multifamily (10+ unit) design playbook
A 24-unit complex is capped at 8 detached ADUs by statute, so the play shifts toward interior conversions: max(1, ⌊units × 25%⌋) = 6 additional units carved from common rooms, oversized lobbies, basement storage, or laundry rooms.
Pro-forma snapshot
| Existing units | 24 |
| Detached ADUs (SB 1211) | 8 |
| Interior conversions | 6 |
| Total new units | 14 |
| Median 1BR rent in San Mateo | $3,000/mo |
| Est. additional gross rent | $504K/yr |
| Estimated total project cost | ~$2,822K |
| Year-1 NOI estimate | ~$378K |
| Stabilized cap rate at cost | 13.4% |
| Replacement parking required | No (§66313) |
| Approval pathway | Ministerial · §66314 |
| Typical permit timeline in San Mateo | 75-130 days |
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