SB 1211 for 12-unit apartment Buildings
If you own a 12-unit apartment, SB 1211 just rewrote your buildable count. A 12-unit apartment. 8 detached ADUs + 3 interior conversions = up to 11 new units.
The math, explained
SB 1211 caps detached ADUs at the lesser of 8 or your existing unit count. A 12-unit 12-unit apartment lot therefore qualifies for 8 detached ADUs. The interior-conversion rule (max(1, ⌊units × 25%⌋)) adds 3 more, for a total of 11.
Design playbook for large multifamily (10+ unit)
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.
Cost expectations
Interior-conversion cost runs $150–$280/sf — meaningfully cheaper than ground-up. Combined with 8 detached ADUs, large-complex projects often see the strongest blended IRR.
What to watch out for
Construction phasing matters: keeping 12 existing tenants in place during a 3-unit interior conversion plus 8 ground-up detached ADUs requires real coordination.
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