The 800 square foot floor
Chapter 30.91 has a rule that shapes almost every Del Mar ADU: the city must accommodate an ADU of at least 800 sq ft, the "universal" size in state law (Del Mar Municipal Code Chapter 30.91 (June 2025)).
How it works
- The first 800 sq ft of an ADU isn't blocked by FAR or lot coverage
- Area above 800 is reviewed against FAR and lot coverage
- If the ADU plus house would exceed FAR or coverage, the house must reduce so an 800 sq ft ADU can still be built
- Several design standards (front setbacks, curb cuts, tree driplines) give way where needed to fit 800 sq ft
The coastal exception
If an 800 sq ft ADU would harm coastal resources or public access protected by the LCP, the city prepares written findings and mitigation, and must still accommodate at least a 150 sq ft efficiency unit.
What it means for design
| Goal | Approach |
|---|---|
| Max certainty | Design at or under 800 sq ft |
| Two bedrooms | Up to 1,000 sq ft detached if FAR allows |
| Remodel too | Watch how the house's added area affects the ADU above 800 |
Checklist
- Existing FAR and lot coverage
- Coastal resources near the site
- Protected trees
- Street setbacks
See ADU size.
Examples of standards that yield to 800 sq ft
| Standard | Yields when needed for 800 sq ft? |
|---|---|
| Street-fronting setbacks | Yes |
| Existing curb cut locations | Yes (ADU under 800 sq ft) |
| Protected tree driplines | Yes, with tree permit, mitigation or penalties |
| Objective design standards | Yes, if they'd prohibit an 800 sq ft ADU |
| Coastal resource protections | No; findings can reduce size |
Source: DMMC §30.91.040.
Questions we hear
- Is 800 sq ft measured inside? Yes, from the inside face of wall studs.
- Can I build 1,000 sq ft? For a detached ADU with more than one bedroom, if FAR and lot coverage allow the area above 800.
- What if I'm remodeling too? The house may need to give up area to preserve 800 sq ft for the ADU.
How state law frames it
The HCD handbook confirms ADU law applies in the Coastal Zone without lessening Coastal Act protections. That's why Del Mar can pair an 800 sq ft floor with coastal findings that reduce size on sensitive lots.
Before you design
- Map trees 4 in or larger and any Torrey Pine or Monterey Cypress drip lines
- Check the FEMA map
- Confirm the appeal zone
- Video the sewer lateral
Also checked Oct 14, 2026: Del Mar ADU Application Packet (Rev. 2024) · HCD ADU Handbook (March 2026).
Sources, checked Oct 14, 2026: Del Mar Municipal Code Chapter 30.91 (June 2025).