800 sq ft ADU · checked Oct 18, 2026
800 sq ft ADU fees in San Diego: $16,137–$20,606, $269 more than at 750 sq ft
San Diego charges no impact fees that we model, so going from 750 to 800 sq ft adds only $269 in size-based fees such as school fees and permits.
750 vs 800
What the extra 50 sq ft changes in San Diego
- School fee (district; statewide cap shown): $0–$4,035 at 750 sq ft → $0–$4,304 at 800 sq ft
Staying at 750 sq ft would save about $269 in fees under today’s law.
Line by line: 750 sq ft vs 800 sq ft, now and under SB 1117
Detached ADU, 2,000 sq ft main home (example assumption). The 2027 column applies SB 1117, which limits impact fees to the area over 750 sq ft.
| Fee | 750 sq ft (2026) | 800 sq ft (2026) | 800 sq ft (from 2027) |
|---|---|---|---|
| Planning & zoning | |||
| General Plan Maintenance Fee | $737 | $737 | $737 |
| Building permit & plan check | |||
| Mapping Fee | $11 | $11 | $11 |
| Building plan check (Table 501A) | $7,539 | $7,539 | $7,539 |
| Building inspection (Table 501A) | $7,834 | $7,834 | $7,834 |
| Water/sewer plan check (no meter change) | May apply$165 | May apply$165 | May apply$165 |
| Fee collection (other agencies) | $16 | $16 | $16 |
| Impact fees | |||
| Development Impact Fees (DIF) | $0 | $0 | $0 |
| School district fee | |||
| School fee (district; statewide cap shown) | Up to$4,035 | Up to$4,304 | Up to$4,304 |
| Modeled total | $16,137–$20,337 | $16,137–$20,606 | $16,137–$20,606 |
State law
Why 800 sq ft is the size every city must allow
Local limits on lot coverage, floor area ratio, open space and minimum lot size can’t stop an 800 sq ft ADU with 4 ft side and rear setbacks, and a detached unit of up to 800 sq ft must be approved ministerially alongside a junior ADU.
Gov. Code §66321(b)(3)
size based upon a percentage of the proposed or existing primary dwelling, or limits on lot coverage, floor area ratio, open space, front setbacks, and minimum lot size, for either attached or detached dwellings that does not permit an accessory dwelling unit with at least 800 square feet of interior livable space and with four-foot side and rear yard setbacks to be constructed in compliance with all other local development standards.
Gov. Code §66323(a)(2)
One detached, new construction, accessory dwelling unit that does not exceed four-foot side and rear yard setbacks for a lot with a proposed or existing single-family dwelling.
Gov. Code §66323(a)(2)(A)
A total floor area limitation of not more than 800 square feet of livable space.
Quoted from Government Code, Title 7, Division 1, Chapter 13 (Accessory Dwelling Units), incl. §66311.5 (opens in new tab), checked Oct 18, 2026.
FAQ
Questions about 800 sq ft adu in San Diego
How much are the fees for an 800 sq ft ADU in San Diego?
Our model of San Diego’s official schedules comes to $16,137–$20,606 for a detached 800 sq ft ADU with a 2,000 sq ft main home, compared with $16,137–$20,337 at 750 sq ft.
Does an 800 sq ft ADU pay impact fees in San Diego?
No impact fees that we model. State law would allow proportional impact fees above 750 sq ft, but San Diego’s schedules we use don’t charge any for this ADU.
Can San Diego stop me from building an 800 sq ft ADU?
Not with lot coverage, floor area ratio, open space or minimum lot size limits. State law requires cities to allow at least an 800 sq ft ADU with 4 ft side and rear setbacks (Gov. Code §66321(b)(3)), provided it meets other objective standards such as height.
Do school fees apply at 800 sq ft?
Yes. School fees apply above 500 sq ft; at 800 sq ft the statewide Level 1 cap is $4,304, and many districts charge less.
Not modeled yet
What these totals leave out
- Water and sewer capacity fees (per EDU, Public Utilities) and County Water Authority meter fees aren’t modeled.
- State strong-motion (SMIP) and building standards fees are small valuation-based state fees and aren’t shown.
- The 2.5-hour DIF assessment review, lead hazard fee (pre-1978 homes only), storm water and express fees aren’t included.
- Projects with more than one ADU also pay the Regional Transportation Congestion Improvement Program fee.
More
Keep going
Sources
Official sources
Every figure comes from these documents; each line’s quoted text is on the San Diego page.
- City of San Diego Development ServicesInformation Bulletin 501: Fee Schedule for Construction Permits – Structures (opens in new tab)
- City of San Diego Development ServicesInformation Bulletin 400: Accessory Dwelling Unit / Junior Accessory Dwelling Unit (opens in new tab)
- City of San Diego City PlanningPublic Spaces: Development Impact Fee FAQ (opens in new tab)
- California State Allocation Board (Department of General Services, OPSC)State Allocation Board item: 2026 adjustment to the Level I developer fee (meeting of January 28, 2026) (opens in new tab)
- California Legislative Information (leginfo.legislature.ca.gov)Government Code, Title 7, Division 1, Chapter 13 (Accessory Dwelling Units), incl. §66311.5 (opens in new tab)
- HCD via data.ca.govHousing Element Annual Progress Report (APR) data, Table A2: ADU building permits by year (opens in new tab)