An ADU builder in San Diego is a licensed contractor who designs and constructs accessory dwelling units — detached backyard units, garage conversions, attached additions, and junior ADUs (JADUs). Because an ADU is a complete second dwelling, the builder coordinates foundation, framing, plumbing, electrical, and HVAC work and pulls it through San Diego's permit process and utility connections. Not every general contractor has built one, so the right builder is one with ADU-specific experience in California.
What ADU Builders Cost in San Diego [18][19][20][21]
Based on our San Diego cost data, expect the following ranges from local ADU builders. Quotes for the same scope typically vary 20-40% between contractors, so getting at least three bids is the single best way to control cost.
| New Detached ADU (all-in) | $250,000-$450,000 |
| Cost per Sq Ft | $375-$600 |
| Garage Conversion | $80,000-$200,000 |
| Prefab / Modular ADU (installed) | $170,000-$325,000 |
| City Permit & Plan Review | 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) |
For a full line-item breakdown, see our San Diego ADU cost guide. To confirm what you're allowed to build before you hire, review the San Diego ADU rules (max detached size: 1,200 sq ft gross floor area (minimum 150 sq ft) for a new attached or detached ADU (SDMC 141.0302(b)(7)). ADU floor area counts toward the lot's floor area ratio, but one ADU of 800 sq ft or less is always allowed and is exempt from FAR, lot coverage, front setback and open-space rules (141.0302(b)(4)). Garage or carport space under an ADU and an exterior-access mechanical closet do not count toward the 1,200 sq ft (DSD FAQ); owner-occupancy: Not required for an ADU (141.0302(b)(11)). A JADU requires the owner to live in the house or the JADU only when the JADU shares a bathroom with the house; a JADU with its own bathroom has no owner-occupancy rule (AB 1154, applied in IB-400 January 2026). A recorded JADU agreement is required before the permit issues (141.0302(c)(1)(F))).
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How to Vet an ADU Builder in San Diego
- License: Confirm a current contractor's license in California and that it's in good standing. Ask for the license number and verify it with the state board.
- ADU-specific experience: Ask how many ADUs they've completed in or near San Diego and request addresses or photos. ADU permitting and setbacks differ from a kitchen remodel.
- Portfolio & references: Get references from recent ADU clients and, if possible, visit a finished unit.
- Insurance: Verify general liability and workers' compensation coverage. Ask for a certificate of insurance.
- Written, detailed bid: Insist on an itemized, fixed-price or clearly-scoped bid — not a verbal estimate. It should state whether permits (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), 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)), and 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)) are included.
- Permit handling: Confirm they manage San Diego's permit process ("Ministerial building permit only (Process One); no planning hearing or public notice (SDMC 141.0302; IB-400). Steps: 1) confirm zone, Coastal Overlay Zone, fire hazard zone, transit priority area and Sustainable Development Area on ZAPP; 2) prepare plans per Project Submittal Manual Section 2A: site plan and vicinity map (IB-122), floor and roof plans, elevations, structural plans and calculations, Title 24 energy forms; 3) submit the General Application (DS-3032), Water Meter Data Card (DS-16) and Storm Water Checklist (DS-560) through the online Development Services portal as a Building Construction application; 4) pay project set-up fees, then DSD Planning, Engineering, Structural and (if needed) Fire review; 5) permit issuance, inspections and, for a JADU, a recorded JADU agreement. Inside the Coastal Overlay Zone an ADU that adds habitable area needs a Coastal Development Permit, issued with the building permit in the non-appealable area (SDMC 126.0708(c)); the city's CDP decision on an ADU is not appealable to the Coastal Commission", typically 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) and who is responsible if revisions are required.
- Payment schedule: Avoid large upfront payments. A reasonable schedule ties payments to completed milestones.
Questions to Ask Before You Hire
- How many ADUs have you built in San Diego in the last two years?
- Is your bid fixed-price, and what would trigger a change order?
- Are permits, plan check, and utility connection fees included?
- What's a realistic timeline, including permit review (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) and construction?
- Who is my point of contact and how are delays communicated?
- What warranty do you provide on workmanship?
- Can you share three recent California ADU client references?
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How much do ADU builders charge in San Diego?
ADU builders in San Diego typically quote $250,000-$450,000 for a new detached unit, or about $375-$600 per square foot, including design, permitting, and construction. A garage conversion runs $80,000-$200,000 and a prefab/modular ADU averages $170,000-$325,000. Add city permit and plan-review 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) plus impact fees of 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). Quotes for the same scope commonly vary 20-40% between builders, so collect at least three bids.
How do I find a good ADU builder in San Diego?
Look for a licensed contractor with completed ADU projects in San Diego specifically — ADUs involve local zoning, setback rules, and utility connections that general remodelers may not have handled. Verify the license, ask for an ADU-specific portfolio and references, confirm they carry liability and workers' comp insurance, and get a written fixed-price or detailed bid. Submit a request below and we'll forward it to local ADU builders serving San Diego for free quotes.
Do ADU builders in San Diego handle permits?
Most full-service ADU builders manage the permit process for you. In San Diego the approval process is "Ministerial building permit only (Process One); no planning hearing or public notice (SDMC 141.0302; IB-400). Steps: 1) confirm zone, Coastal Overlay Zone, fire hazard zone, transit priority area and Sustainable Development Area on ZAPP; 2) prepare plans per Project Submittal Manual Section 2A: site plan and vicinity map (IB-122), floor and roof plans, elevations, structural plans and calculations, Title 24 energy forms; 3) submit the General Application (DS-3032), Water Meter Data Card (DS-16) and Storm Water Checklist (DS-560) through the online Development Services portal as a Building Construction application; 4) pay project set-up fees, then DSD Planning, Engineering, Structural and (if needed) Fire review; 5) permit issuance, inspections and, for a JADU, a recorded JADU agreement. Inside the Coastal Overlay Zone an ADU that adds habitable area needs a Coastal Development Permit, issued with the building permit in the non-appealable area (SDMC 126.0708(c)); the city's CDP decision on an ADU is not appealable to the Coastal Commission" with a typical review timeline of 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. Confirm in writing whether permit fees, 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)), and impact fees are included in the bid or billed separately.
How long does it take to build an ADU in San Diego?
Plan for the permit review (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 in San Diego) plus construction. Most detached ADUs take 4-8 months of construction after permits are issued; garage conversions and prefab units are often faster. Ask each builder for a realistic schedule and what could delay it.
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