How big can a Del Mar ADU be?
Del Mar's code gives clear numbers, with one coastal exception (Del Mar Municipal Code Chapter 30.91 (June 2025)).
| Type | Maximum |
|---|---|
| Detached ADU | 850 sq ft; 1,000 sq ft with more than one bedroom |
| Attached ADU | 50% of the house's habitable space; 800 sq ft if the house is under 1,600 sq ft |
| Converted (within existing walls) | Existing space plus 150 sq ft for ingress/egress |
| JrADU | 500 sq ft |
| Universal size | At least 800 sq ft must be accommodated |
Source: DMMC §30.91.040(G), §30.91.050.
How it's measured
All interior floor space from the inside face of wall studs counts, whether or not it would count as floor area elsewhere in the code.
FAR and the 800 sq ft rule
The first 800 sq ft is protected. Area above 800 is reviewed against FAR and lot coverage, and if the ADU plus house would exceed them, the house must shrink to preserve at least an 800 sq ft ADU.
The coastal exception
If an 800 sq ft ADU would impact coastal resources or public access protected by the LCP, the city prepares written findings and mitigation to accommodate an ADU of at least 150 sq ft (an efficiency unit).
Questions homeowners ask
- Does a bedroom count change the limit? Yes, for detached ADUs: more than one bedroom allows 1,000 sq ft. Attached ADUs are 50% regardless of bedrooms.
- What counts as a bedroom? An enclosed sleeping space with a door separating it from the kitchen, living room and hallways.
Sources, checked Oct 14, 2026: Del Mar Municipal Code Chapter 30.91 (June 2025).
Questions
What's the maximum ADU size in Del Mar?
850 sq ft, or 1,000 sq ft with more than one bedroom, for detached ADUs; attached ADUs are capped at 50% of the house.
Must Del Mar allow an 800 sq ft ADU?
Yes, unless it would impact coastal resources or public access, in which case findings can reduce it to no less than 150 sq ft.