SB 1211 for 20-unit apartment in San Mateo
A 20-unit 20-unit apartment in San Mateo qualifies for up to 13 new homes under SB 1211 — 8 detached ADUs and 5 interior conversions. At San Mateo's median rent of $3,000/mo, that's ~$468K in additional gross annual rent.
The San Mateo scenario
The scenario most San Mateo 20-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.
San Mateo watch: Peninsula tech rents; very strong upside.
Large multifamily (10+ unit) design playbook
A 20-unit complex is capped at 8 detached ADUs by statute, so the play shifts toward interior conversions: max(1, ⌊units × 25%⌋) = 5 additional units carved from common rooms, oversized lobbies, basement storage, or laundry rooms.
Pro-forma snapshot
| Existing units | 20 |
| Detached ADUs (SB 1211) | 8 |
| Interior conversions | 5 |
| Total new units | 13 |
| Median 1BR rent in San Mateo | $3,000/mo |
| Est. additional gross rent | $468K/yr |
| Estimated total project cost | ~$2,621K |
| Year-1 NOI estimate | ~$351K |
| 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 |
Get a personalized SB 1211 feasibility report for 20-unit apartment owners in San Mateo
3 minutes. We email you a 4-page PDF with your buildable count, parking determination, jurisdiction overlays, and pro-forma.
No spam · free · delivered in 24 hrs