SB 1211 for Triplex Buildings
If you own a triplex, SB 1211 just rewrote your buildable count. A 3-unit residential building. SB 1211 allows up to 3 detached ADUs on existing triplex lots.
The math, explained
SB 1211 caps detached ADUs at the lesser of 8 or your existing unit count. A 3-unit triplex lot therefore qualifies for 3 detached ADUs. The interior-conversion rule (max(1, ⌊units × 25%⌋)) adds 1 more, for a total of 4.
Design playbook for small multifamily (2–4 unit)
Small multifamily lots are usually constrained on width before they're constrained on count. With a 3-unit existing footprint, the binding constraint becomes side-yard setbacks (4 ft min) and the 18-ft height limit. Two-story stacked-flat ADUs over surface parking are the highest-yield typology.
Cost expectations
Stick-built unit cost on small lots typically runs $300–$450/sf. Modular drops that to $220–$320/sf, and SB 1211's ministerial pathway makes pre-approved factory plans the fastest route to occupancy.
What to watch out for
Watch for: shared utility laterals (sewer especially), fire access on narrow lots, and tree-protection ordinances that survive ministerial review.
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