ADU Cost Guide · 2026
How Much Does an ADU Cost in San Diego? (2026)
Real numbers from a licensed San Diego design-build contractor — broken down by ADU type, what drives costs up, and how to budget without getting surprised.
ADU Cost Ranges by Type
ADU costs in San Diego vary enormously depending on type, size, site conditions, and finishes. Here are realistic ranges for 2026:
| ADU Type | Typical Cost Range | Key Cost Drivers |
|---|---|---|
| Junior ADU (JADU) | $40,000–$90,000 | Kitchen addition, separate entrance, electrical upgrade |
| Garage Conversion | $80,000–$150,000 | Insulation, HVAC, plumbing rough-in, foundation upgrades |
| Attached ADU | $150,000–$280,000 | Foundation extension, roof tie-in, shared wall work |
| Detached ADU (prefab) | $130,000–$220,000 | Site prep, utility connections, foundation |
| Detached ADU (custom-built) | $200,000–$380,000 | Full custom construction, design fees, permits |
Why San Diego ADUs Cost More Than the State Average
San Diego's labor costs, impact fees, soil conditions, and coastal permitting requirements push ADU costs 20–30% above the California average. A 600 sqft detached ADU that costs $180,000 in Sacramento might run $230,000 in San Diego. Budget accordingly.
What's Included in a Typical ADU Build Cost
For a custom-built 600 sqft detached ADU in San Diego, here's how a $265,000 budget typically breaks down:
| Cost Category | Typical Share | Dollar Range |
|---|---|---|
| Foundation & site work | 12–15% | $31,800–$39,750 |
| Framing & structure | 15–18% | $39,750–$47,700 |
| Roofing | 4–6% | $10,600–$15,900 |
| Windows & doors | 4–6% | $10,600–$15,900 |
| Electrical | 6–8% | $15,900–$21,200 |
| Plumbing | 8–10% | $21,200–$26,500 |
| HVAC | 4–5% | $10,600–$13,250 |
| Insulation & drywall | 4–5% | $10,600–$13,250 |
| Flooring | 3–5% | $7,950–$13,250 |
| Kitchen & bath finishes | 8–12% | $21,200–$31,800 |
| Exterior finish & paint | 3–4% | $7,950–$10,600 |
| Design, permits & fees | 8–12% | $21,200–$31,800 |
The Hidden Costs That Catch San Diego Homeowners Off Guard
The quoted build cost is rarely the final number. These items frequently add $20,000–$80,000 to a San Diego ADU project:
- Impact fees: ADUs 750 sqft and larger pay full development impact fees in San Diego — $15,000–$45,000 depending on location and unit size
- School fees: San Diego Unified charges approximately $4.79/sqft for new residential construction (2026 rate)
- Utility connections: A new water meter and sewer lateral connection can add $8,000–$25,000 depending on distance from street
- Grading and drainage: Sloped lots or lots with poor drainage require additional site work — budget $5,000–$20,000
- Panel upgrade: Most older San Diego homes need a 200-amp panel upgrade before adding an ADU — $3,000–$6,000
- Solar requirement: California Title 24 requires new ADUs to include solar panels — typically $8,000–$15,000 or a documented exception
Garage Conversion: The Most Cost-Effective ADU Path
If you have an attached or detached garage, conversion is almost always the most affordable ADU path. The structure is already there — you're adding insulation, HVAC, plumbing, electrical, and interior finishes rather than building from scratch.
- Typical range: $80,000–$150,000 for a two-car garage (400–500 sqft)
- No new foundation: Existing slab is used, though it may need moisture barrier work
- Setback advantage: The existing garage already satisfies setback requirements
- Permit pathway: Garage conversions follow a simpler permit path than new construction ADUs
- Timeline: Typically 8–14 weeks from permit approval to move-in
- Trade-off: You lose the garage — relevant in San Diego neighborhoods where street parking is limited
ROI on San Diego ADUs
A well-built $250,000 ADU in San Diego can generate $2,200–$3,500/month in rental income, yielding a 10–17% gross annual return. In high-demand neighborhoods like North Park, Hillcrest, and Ocean Beach, ADUs rent quickly and command premium rates. ADUs also add appraised value — typically 60–80% of build cost in immediate equity.
Frequently Asked Questions
Answers to what San Diego homeowners ask most.
A garage conversion is almost always the most affordable path — $80,000–$150,000 versus $200,000–$380,000 for new construction. A Junior ADU (converting an existing room with a kitchenette and separate entrance) can be done for $40,000–$90,000.
From initial design through move-in, expect 9–18 months for a custom detached ADU (permit review alone takes 60–90 days). Garage conversions typically take 6–12 months total. Prefab ADUs can compress the build timeline to 3–4 months once permits are approved.
Yes. California state law prohibits cities from charging impact fees on ADUs under 750 sqft. This makes 749 sqft a common target size for ADU projects trying to minimize fee exposure while maximizing usable space.
Yes, but only by the assessed value of the ADU improvement — your existing home's assessed value isn't re-assessed. California's Prop 13 protections apply to the original home. The ADU addition is assessed at current market value, typically adding $2,000–$5,000/year in property taxes.
Owner-builders can pull permits in California, but ADU construction involves structural, electrical, plumbing, and mechanical work that requires licensed subcontractors in San Diego. Most owner-builder attempts save 10–15% but add 6–12 months to the timeline and increase the risk of code violations.
For rental income, a 600–749 sqft one-bedroom ADU hits the sweet spot — it stays under the impact fee threshold, is large enough to command strong rents, and doesn't consume the entire backyard. For multigenerational living, a 900–1,200 sqft two-bedroom unit is more practical.
Have a question not covered here? Call (831) 261-7329 or send us a message. We answer the phone.
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