ADU rules in Santa Monica
The key facts first, then what we've learned building there.
The snapshot
Checked October 2026. We re-check every lot against the current code.
Santa Monica
| Rule | Answer |
|---|---|
| Detached ADU size | Up to 1,200 sq ft |
| Setbacks | 4 ft side and rear |
| Height | 16 ft; 18 ft near transit; 25 ft attached |
| Selling an ADU separately | Allowed: Santa Monica opted in to AB 1033 in October 2025 |
| Coastal zone | Parts of the city are in the coastal zone and need a coastal development permit |
| Seismic retrofit | A 2017 mandatory program covers soft-story, older concrete, steel frame, tilt-up and brick buildings |
| Rent control | The city has its own rent control; we check a building's status before design |
| SB 1211 apartment ADUs | Yes |
| Building department | Planning and Building & Safety |
What's different here
Since October 2025, Santa Monica lets an ADU be sold separately as a condo, with conditions.
Near the beach, an ADU may need a coastal development permit on top of the building permit.
Older apartment buildings may be on the city's mandatory seismic list. We look at both together, so the retrofit and the ADUs share one plan.
Many older buildings fall under the city's rent control. We flag it before design so there are no surprises.
What applies here
Since January 2025, California lets an existing apartment property add detached ADUs, one for every existing unit up to eight, plus conversions of garages and storage.
Learn moreTurn an older unpermitted unit into a legal, rentable home.
Learn moreCities must now keep a set of pre-approved ADU plans.
Learn moreSB 9 lets a single-family lot be split in two, with up to two homes on each.
Learn morePlans that fit
Ready-drawn plans we adapt to your lot and your city.
Ask about your address
We check the lot against these rules and tell you what fits.