ADU rules in Unincorporated San Diego County
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.
Unincorporated San Diego County
| 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 |
| Pre-approved plans | Yes: free county plans since 2019, in 600 and 1,200 sq ft sets |
| What you still add | A site plan, stormwater form, energy calculations and truss design (the county sets are about 85% complete) |
| Selling an ADU separately | Allowed: the county adopted an AB 1033 program on March 4, 2026 |
| Rural lots | Septic and well review may apply |
| Fire zones | Much of the back country is mapped fire hazard; ember-resistant construction applies |
| Utilities | SDG&E |
| Building department | Planning & Development Services (PDS) |
What's different here
The county offers free ADU plans in 600 and 1,200 sq ft sizes. They are about 85% complete: we add the site plan, stormwater form, energy calculations and truss design for your lot.
Since March 2026 the county lets an ADU be sold separately as a condo, with conditions.
On larger lots outside the cities, septic, well and long utility runs shape where the ADU goes. We check them first.
Large parts of the county are fire hazard zones, which bring ember-resistant materials and access checks.
What applies here
Cities 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 moreSince 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 moreRebuild after a fire, with an ADU to live in or rent while the main house goes up.
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.