ADU Cost in San Diego (2026)
Build cost · Rental income · Payback
San Diego County · Fees checked 2026-10-06
For a 600 sq ft detached ADU in San Diego, LotFoundry's planning model estimates $231,000 to $289,000 to build, including an allowance for design and permit soft costs. At San Diego County's HUD Fair Market Rent of $2,459 a month, simple payback is about 12.6 years.
These are planning estimates for a new detached backyard home, whether it is for family, for rental income or for what comes next. Rent uses San Diego County's HUD Fair Market Rent, so the rent and payback figures hold across the county. Build cost uses LotFoundry's national construction base rather than a San Diego contractor survey, so compare it with site-specific quotes before you set a budget.
ADU build cost in San Diego by size
Cedar finish and a shed roof, with the soft-cost allowance included. Smaller units cost more per square foot because fixed costs spread over less floor area.
| Unit size | Estimated build cost | Per sq ft |
|---|---|---|
| 400 sq ft | $157K–$197K | $393–$493 |
| 600 sq ft | $231K–$289K | $385–$482 |
| 800 sq ft | $305K–$381K | $381–$476 |
| 1,200 sq ft | $453K–$566K | $378–$472 |
Estimate your ADU
- Build cost
- $231K–$289K
- Rent per month
- $2,459
- Simple payback
- 12.6 years
A 600 sq ft ADU in San Diego County nets about $19,918 a year after operating costs. These are countywide estimates, not a quote for your lot.
Itemized budget breakdown
Construction and soft costs itemize the model without adding fees twice. Site work and financing are unpriced until you have site-specific quotes.
- Construction (hard costs)
600 sq ft · Cedar · openings ($9K)
$213,000Model allowance
- Design & permits (soft costs)
18% allowance for architectural plans & municipal fees
$38,34018% allowance
- Site work
Grading, utility trenching, tie-ins, foundation prep
UnpricedSite-specific
- Financing & loan costs
Interest during build, origination, closing
UnpricedLoan-dependent
- Itemized total midpoint$251,340
Free address check
Countywide tools can't check lot boundaries or setbacks. Enter your California address to see property lines, base-zone setbacks, and a placed ADU in 3D.
What a San Diego ADU rents for, and when it pays back
Studio rent for 400 sq ft, one-bedroom for 600 and 800 sq ft, and two-bedroom for 1,200 sq ft, at the county's HUD Fair Market Rent. Simple payback divides the midpoint build cost by a year of rent after operating costs.
| Unit size | Projected rent/mo | Simple payback |
|---|---|---|
| 400 sq ft | $2,090 estimate | 10.1 years estimate |
| 600 sq ft | $2,459 estimate | 12.6 years estimate |
| 800 sq ft | $2,459 estimate | 16.6 years estimate |
| 1,200 sq ft | $3,123 estimate | 19.5 years estimate |
Citywide estimates — payback on your lot depends on your buildable envelope, your build size, and your neighborhood rent. HUD FMR · San Diego County, CA · HUD FY2026 FMR (effective 2026-05-21; seed extract) · Medium confidence.
These are countywide estimates. Here is what they mean for your lot.
Enter your San Diego address to see rent, build-cost, and payback estimates for your specific parcel. Free to explore — no account needed for your first address.
City of San Diego permit and impact fees
Inside City of San Diego limits, use Development Services Information Bulletin 501 to price plan review and inspection for your project. The schedule distinguishes detached ADUs up to 500 square feet from larger detached units, and attached units have separate size categories. There is no single permit price per square foot for every ADU.
California's March 2026 ADU Handbook says ADUs with 750 square feet of interior livable space or less are exempt from local impact fees; larger units are charged proportionately to the primary dwelling. School fees and utility connection charges have separate rules, so request an itemized assessment.
The model's soft-cost allowance already covers design, engineering and permits. Reconcile your actual fees against it rather than adding them twice.
- Plan review and inspection: use the applicable project category in Bulletin 501
- Local impact fees: exempt at 750 sq ft of interior livable space or less; proportional above
- School fees: confirm the applicable assessment with your school district
- Utility connections and capacity charges: request provider-specific estimates
- Official fee schedule: Information Bulletin 501 (Fee Schedule for Construction Permits - Structures)
What the estimate includes
- Hard construction cost of $315–$355 per sq ft depending on the exterior finish, plus a roof-style premium and $9,000 for windows and doors. This is a national cost base, not a San Diego contractor survey.
- A 18% allowance on top for design, engineering and permits. The range runs from 8% below to 15% above that midpoint.
- Rent from San Diego County's HUD Fair Market Rent, with 32.5% of it set aside for vacancy, management, maintenance, insurance, utilities and property tax.
- Not included: land, unusual site work such as long utility runs or retaining walls, financing costs, and conversions of existing space.
HUD FMR · San Diego County, CA · HUD FY2026 FMR (effective 2026-05-21; seed extract) · Medium confidence.
Garage conversions and junior ADUs
Every figure on this page prices a new detached unit. A garage conversion, or a junior ADU (JADU) inside the house, reuses walls, a roof and often utilities, so its cost depends on what is already there. The model does not price conversions.
San Diego allows one JADU, one converted ADU and one new detached or attached ADU on the same single-family lot. If you are weighing a conversion against a new backyard home, price both from a site visit: structural work, fire separation and utility capacity decide the difference.
What to ask for in a San Diego ADU quote
Ask the builder to separate the costs below and to mark which items are allowances and which are excluded, so two quotes cover the same scope.
Use the tables to compare sizes; use the City's current fee schedule and a site-specific quote for your budget.
- Construction of the unit itself
- Design and engineering, including structural and Title 24 energy calculations
- City plan check and permit fees
- Utility connections
- Site work such as grading, access and demolition
Elsewhere in San Diego County
The rent and payback figures use the countywide HUD rent, so they apply across San Diego County. Rules and fees change at the city line: read the guide for the jurisdiction that reviews your property.
- ADU rules in San Diego — setbacks, overlays and permit steps for the City of San Diego
- ADU rules in Chula Vista
- ADU rules in Oceanside
- ADU rules in Escondido
- ADU rules in Carlsbad
San Diego ADU cost questions, answered
How much does an ADU cost to build in San Diego?
LotFoundry's model estimates $157,000 to $197,000 for a 400 sq ft unit, $231,000 to $289,000 for 600 sq ft, and $453,000 to $566,000 for 1,200 sq ft, including a soft-cost allowance. These are planning estimates, not a contractor quote.
What does an ADU cost per square foot in San Diego?
About $378 to $493 per square foot all-in across the sizes on this page. Smaller units cost more per square foot because fixed costs such as windows and doors spread over less floor area.
How much rent can an ADU earn in San Diego?
San Diego County's HUD Fair Market Rent is $2,090 a month for a studio, $2,459 for one bedroom and $3,123 for two bedrooms. Treat these as estimates and check current listings near you.
How long does an ADU take to pay for itself in San Diego?
On the model's conservative rent, simple payback runs from about 10.1 years for 400 sq ft to 19.5 years for 1,200 sq ft. It ignores financing, taxes and appreciation, so use it to compare options, not as a forecast.
Does the estimate include permit fees?
Partly. The model adds a soft-cost allowance for design, engineering and permits on top of construction. Compare your actual design quote and the City's Information Bulletin 501 fees against that allowance rather than adding them on top.
Is a garage conversion cheaper than a new ADU in San Diego?
It can be, because the walls and roof already exist, but the model does not price conversions. Structural work, fire separation and utility upgrades decide the real cost, so get a quote from a site visit.
Do these numbers apply outside the City of San Diego?
The rent and payback figures do, because they use San Diego County's HUD Fair Market Rent. Fees do not: Chula Vista, Oceanside, Escondido, Carlsbad and the unincorporated county each set their own, so check the guide for your address.
Why is the San Diego build cost the same as in Los Angeles?
The model prices construction on one national cost base until a verified regional factor is available; only rent is local. A San Diego builder's quote can differ, so treat the table as a starting point.
Sources and as-of date
Fee figures were checked against the sources below on 2026-10-06; rent figures carry their HUD vintage above. Confirm current fees with the City before you budget.
These are countywide estimates. Here is what they mean for your lot.
Enter your San Diego address to see rent, build-cost, and payback estimates for your specific parcel. Free to explore — no account needed for your first address.
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