Attached ADUs in Del Mar
In Del Mar an attached ADU is an addition that shares a common wall with the house. The city's code is specific about where it can go and how tall it can be, and building one means no junior ADU on the lot (Del Mar Municipal Code Chapter 30.91 (June 2025)).
Attached ADU standards
| Standard | Del Mar rule |
|---|---|
| Definition | Addition sharing a common wall horizontally with the house |
| Size | 50% of the house's habitable space, regardless of bedrooms; 800 sq ft if the house is under 1,600 sq ft |
| Story | First story if there's enough buildable area |
| Height, first story | 16 ft |
| Height, second story | Only if needed to fit up to 800 sq ft; 25 ft or zone height, whichever is lower; never over two stories |
| Bluff, Slope and Canyon Overlay | 14 ft maximum |
| JrADU | Not allowed with an attached ADU |
| Garage option | An ADU may attach to an existing attached or detached garage |
Source: DMMC §30.91.040(B), (G), (K).
Attached vs detached in Del Mar
| Attached | Detached | |
|---|---|---|
| Size cap | 50% of house (or 800 sq ft) | 850 / 1,000 sq ft |
| JrADU allowed | No | Yes |
| Height | 16 ft first story | 16 ft (18 ft near transit) |
| Coastal permit | May be exempt if it qualifies under Coastal Commission regulation 13250 | Administrative CDP |
| Solar | Not required | Required if new and non-manufactured |
Source: DMMC §30.91.030(E), §30.91.040.
Nonconforming houses
If the house is nonconforming for geologic setbacks, public views, coastal access or habitat buffers, and the ADU work amounts to redevelopment (50% of major structural components replaced, or a 50% increase in floor area), the city requires those conditions to be corrected.
Step by step
- Measure the house's habitable space
- Check first-story buildable area
- Design to the objective standards, matching style if within 20 ft
- Submit packet, fees and plans; engineering review applies to attached ADUs
- Record the deed restriction
- Build and inspect
Questions homeowners ask
- Is an attached ADU cheaper than detached? It can be: no solar requirement and possible coastal permit exemption. But Del Mar's 50% size cap and loss of the JrADU option matter.
- Can I build a second-story ADU over my house? Only if there isn't enough first-story area and it's needed to fit up to 800 sq ft.
Why Del Mar prefers the first story
The code says attached ADUs in single dwelling zones are to be proposed at the first story if there's enough buildable area. That reflects the certified LCP's focus on bulk, scale and public views. A second-story attached ADU is the fallback, allowed only to fit up to 800 sq ft when the ground floor can't.
Design standards that bite on additions
An attached ADU must match the house's architectural style, roof pitch, materials, colors and finishes, down to windows, doors, light fixtures, hardware and railings. Each elevation needs at least one projection, offset or recess of a foot or more every 20 ft. Windows facing neighbors must be offset from theirs, or use obscured glass, clerestories or high sills. Glass walls visible from neighbors aren't allowed, and skylights must be tinted.
Coastal permit: possibly exempt
An ADU directly attached to an existing single-family residence is exempt from the Administrative CDP if it qualifies as exempt development under Section 13250 of the Coastal Commission's regulations. We check this early because it changes the process: no site notice card, no mailed notice of approval.
Checklist
- House habitable area measured
- First-story area available
- Matching materials schedule
- Window offsets studied
- Coastal exemption checked
Sources, checked Oct 14, 2026: Del Mar Municipal Code Chapter 30.91 (June 2025).
Questions
What does an attached ADU mean in Del Mar?
An addition that shares a common wall horizontally with the house. Building one means no JrADU on the lot.
How big can an attached ADU be in Del Mar?
50% of the house's habitable space, or 800 sq ft if the house is under 1,600 sq ft.