SB 1211 for 12-unit apartment in San Mateo
Own a 12-unit apartment in San Mateo? SB 1211 lets you stack 11 new units on top of your existing 12: 8 detached + 3 interior. At San Mateo's median rent of $3,000/mo, that's ~$396K in additional gross annual rent.
The San Mateo scenario
Picture the typical case: a 12-unit 12-unit apartment on a San Mateo block built between 1955 and 1975, with surface parking that hasn't been fully utilized in years. SB 1211 turns that parking into 8 detached units plus 3 interior conversions — 11 new doors that didn't exist before 2024.
Local tip for San Mateo: Peninsula tech rents; very strong upside.
Large multifamily (10+ unit) design playbook
A 12-unit complex is capped at 8 detached ADUs by statute, so the play shifts toward interior conversions: max(1, ⌊units × 25%⌋) = 3 additional units carved from common rooms, oversized lobbies, basement storage, or laundry rooms.
Pro-forma snapshot
| Existing units | 12 |
| Detached ADUs (SB 1211) | 8 |
| Interior conversions | 3 |
| Total new units | 11 |
| Median 1BR rent in San Mateo | $3,000/mo |
| Est. additional gross rent | $396K/yr |
| Estimated total project cost | ~$2,218K |
| Year-1 NOI estimate | ~$297K |
| 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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