SB 1211 for 20-unit apartment Buildings
A 20-unit complex. 8 detached + 5 interior = up to 13 new units.
The math, explained
SB 1211 caps detached ADUs at the lesser of 8 or your existing unit count. A 20-unit 20-unit apartment lot therefore qualifies for 8 detached ADUs. The interior-conversion rule (max(1, ⌊units × 25%⌋)) adds 5 more, for a total of 13.
Design playbook for large multifamily (10+ unit)
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.
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 20 existing tenants in place during a 5-unit interior conversion plus 8 ground-up detached ADUs requires real coordination.
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