Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your San Diego ADU cost →Building an ADU in San Diego costs between $250,000-$450,000 for new construction, with per-square-foot costs averaging $375-$600. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $80,000-$200,000, while prefab/modular ADUs fall in between at $170,000-$325,000.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | IB-501 (August 2026), Table 501A: a detached ADU of 500 sq ft or less, or an attached ADU or JADU up to 1,100 sq ft, pays $3,512.92 plan check plus $2,228.29 inspection for the first 500 sq ft ($5,741.21) and $6.98 + $4.46 per sq ft above that (about $9,173 for an 800 sq ft attached unit). A detached ADU over 500 sq ft is billed at the single-dwelling-unit rate: $8,085.26 plan check plus $8,401.90 inspection ($16,487.16 flat up to 3,000 sq ft including attached accessory structures). Every project also pays the $737 General Plan Maintenance Fee, a $12.16 mapping fee, a 2.5-hour DIF-calculation review (about $442 at the $176.84 hourly rate), $529.71 per new address, water/sewer plan check of $176.57 (no meter change) or $353.13 (new meter), and state seismic and building-standards fees. School district fees apply to any ADU of 500 sq ft or more (IB-146). Express plan check costs $793.95 plus 1.5x the regular plan check fee |
| Impact Fees | Citywide Development Impact Fees (parks, fire, library, mobility) are waived for the first two ADUs on a lot regardless of size, for any ADU under 750 sq ft, for every JADU, and for any ADU where the owner records an affidavit to live on the property for three years (SDMC 142.0640(b)(1), adopted by O-21439 and certified citywide in 2024). A third or later ADU of 750 sq ft or more pays the citywide DIF from the Public Spaces calculator, and projects with more than one ADU owe Regional Transportation Congestion Improvement Program fees. Bonus and affordable ADUs pay a Community Enhancement Fee equal to the multifamily DIF for the unit's size: on the FY2027 schedule about $17,342 for a unit of 500 sq ft or less and $20,166 at 701-750 sq ft, with the park share added for fee dates on or after May 20, 2026; low- and very-low-income units in High or Highest Resource areas are exempt. A detached ADU that needs its own water meter or sewer connection can also owe Public Utilities capacity charges ($3,047 water and $5,154 sewer per equivalent dwelling unit on the schedule DSD links from IB-501; confirm current amounts). ADUs are not exempt from inclusionary housing fees, which apply once a project reaches 10 units (5 in the Coastal Overlay Zone) |
| Site Prep & Foundation | $10,000 – $35,000 |
| Framing & Structure | $15,000 – $45,000 |
| Plumbing | $8,000 – $20,000 |
| Electrical | $5,000 – $15,000 |
| HVAC | $3,000 – $8,000 |
| Interior Finishes | $15,000 – $40,000 |
Quotes for the same ADU commonly vary 20–40% between builders. We pass your request to up to 5 local builders serving San Diego, where we have them — free, no obligation.
Get San Diego builder quotes →Permit fees in San Diego are IB-501 (August 2026), Table 501A: a detached ADU of 500 sq ft or less, or an attached ADU or JADU up to 1,100 sq ft, pays $3,512.92 plan check plus $2,228.29 inspection for the first 500 sq ft ($5,741.21) and $6.98 + $4.46 per sq ft above that (about $9,173 for an 800 sq ft attached unit). A detached ADU over 500 sq ft is billed at the single-dwelling-unit rate: $8,085.26 plan check plus $8,401.90 inspection ($16,487.16 flat up to 3,000 sq ft including attached accessory structures). Every project also pays the $737 General Plan Maintenance Fee, a $12.16 mapping fee, a 2.5-hour DIF-calculation review (about $442 at the $176.84 hourly rate), $529.71 per new address, water/sewer plan check of $176.57 (no meter change) or $353.13 (new meter), and state seismic and building-standards fees. School district fees apply to any ADU of 500 sq ft or more (IB-146). Express plan check costs $793.95 plus 1.5x the regular plan check fee. The review timeline is State law: the city must approve or deny within 60 days of a complete application or the ADU is deemed approved (Gov. Code 66314, SB 543 effective January 1, 2026); pre-approved plans get a 30-day review (IB-400). DSD's live dashboard on September 18, 2026 showed about 2 days in intake, 12-18 calendar days for a first review (Structural 12, Combined 16, Planning and Engineering 18), 6-13 days per recheck and 2 business days for issuance; expect one or two correction cycles, with plan check: Fully digital plan check through the DSD online portal, with a single consolidated resubmittal after all disciplines finish a cycle. Fire sprinklers are required only if the main house has them; a detached ADU never triggers sprinklers in the existing house (141.0302(a)(6)); all bonus and affordable ADUs must be sprinklered (141.0302(d)(5)). A new detached, site-built ADU must include solar panels under the California Energy Code (they may go on the main house); conversions and JADUs are exempt. An ADU over four units on a lot triggers Mobility Choices review, and every ADU needs code-compliant refuse and recycling storage (SDMC 142.0801). Impact fees are Citywide Development Impact Fees (parks, fire, library, mobility) are waived for the first two ADUs on a lot regardless of size, for any ADU under 750 sq ft, for every JADU, and for any ADU where the owner records an affidavit to live on the property for three years (SDMC 142.0640(b)(1), adopted by O-21439 and certified citywide in 2024). A third or later ADU of 750 sq ft or more pays the citywide DIF from the Public Spaces calculator, and projects with more than one ADU owe Regional Transportation Congestion Improvement Program fees. Bonus and affordable ADUs pay a Community Enhancement Fee equal to the multifamily DIF for the unit's size: on the FY2027 schedule about $17,342 for a unit of 500 sq ft or less and $20,166 at 701-750 sq ft, with the park share added for fee dates on or after May 20, 2026; low- and very-low-income units in High or Highest Resource areas are exempt. A detached ADU that needs its own water meter or sewer connection can also owe Public Utilities capacity charges ($3,047 water and $5,154 sewer per equivalent dwelling unit on the schedule DSD links from IB-501; confirm current amounts). ADUs are not exempt from inclusionary housing fees, which apply once a project reaches 10 units (5 in the Coastal Overlay Zone). Pre-approved plans: Yes. Under AB 1332 the city accepts three outside catalogs of pre-approved plans, the County of San Diego Standard ADU Plans, the City of Chula Vista Standard ADU Plans and the City of Encinitas Permit-Ready ADU Plans, with a 30-day review; the plans must be licensed from their designer and re-checked against current codes and the SDMC development standards (DSD ADU page; IB-400). Applicants may also have their own plans pre-approved for others through the master plan process in IB-114a; the city does not publish a count of such plans.
| 1-Bedroom Rent | $2,200-$2,700/month |
| 2-Bedroom Rent | $3,000-$3,300/month |
| Annual Rental Income (est.) | $29,400/year |
| Payback Period (est.) | 11.9 years |
| Short-Term Rental | No. An ADU may not be rented for less than 31 consecutive days (SDMC 141.0302(a)(8)); a JADU must be rented for longer than 30 days and may not be used for Short-Term Residential Occupancy (IB-400; AB 1154). |
| Overall ROI Estimate | 6-10% gross rental yield on a $250,000-$450,000 detached build at $2,200-$2,700/mo (5.9-13% on the raw ranges), before vacancy, taxes and financing; a garage conversion costs a third to a half as much and yields proporti. |
A typical ADU in San Diego generates approximately $29,400 per year in rental income based on average 1-bedroom rents. At an average construction cost of $350,000, the estimated payback period is 11.9 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in San Diego and varies by market (often less than build cost).
1. Garage conversions save 40-60% vs new construction since the shell already exists. Average cost in San Diego: $80,000-$200,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $170,000-$325,000.
3. Pre-approved plans — available in San Diego, which can save $3,000-$10,000 in design costs and 2-3 months in review time. See which cities offer pre-approved ADU plans.
4. State grants — California's CalHFA ADU grant (up to $40K) is currently paused; check calhfa.ca.gov/adu for status and your state for active programs.
5. Get multiple bids — ADU contractor pricing varies 20-40% for the same project. We recommend getting at least 3 quotes.
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