800 sq ft ADU · checked Oct 18, 2026
800 sq ft ADU fees in Palo Alto: $20,090–$30,394, $18,359 more than at 750 sq ft
At 800 sq ft an ADU crosses the 750 sq ft line, so Palo Alto’s impact fees apply in proportion to the main home: $18,090 with a 2,000 sq ft house, against $0 at 750 sq ft. From January 1, 2027, SB 1117 limits them to the 50 sq ft over 750, which our model puts at $1,131.
750 vs 800
What the extra 50 sq ft changes in Palo Alto
- Parks impact fee (single family): $0 at 750 sq ft → $15,000 at 800 sq ft (exempt at 750)
- Community center impact fee: $0 at 750 sq ft → $1,152 at 800 sq ft (exempt at 750)
- Libraries impact fee: $0 at 750 sq ft → $688 at 800 sq ft (exempt at 750)
- Public safety facilities impact fee: $0 at 750 sq ft → $553 at 800 sq ft (exempt at 750)
- General government facilities impact fee: $0 at 750 sq ft → $697 at 800 sq ft (exempt at 750)
- School fees (Palo Alto Unified): $0–$4,035 at 750 sq ft → $0–$4,304 at 800 sq ft
Staying at 750 sq ft would save about $18,359 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) |
|---|---|---|---|
| Building permit & plan check | |||
| Building permit fees (City's typical range) | Est.$2,000–$8,000 | Est.$2,000–$8,000 | Est.$2,000–$8,000 |
| Impact fees | |||
| Parks impact fee (single family) | Exempt | $15,000 | $938 |
| Community center impact fee | Exempt | $1,152 | $72 |
| Libraries impact fee | Exempt | $688 | $43 |
| Public safety facilities impact fee | Exempt | Est.$553 | Est.$35 |
| General government facilities impact fee | Exempt | Est.$697 | Est.$44 |
| School district fee | |||
| School fees (Palo Alto Unified) | Up to$4,035 | Up to$4,304 | Up to$4,304 |
| Modeled total | $2,000–$12,035 | $20,090–$30,394 | $3,131–$13,435 |
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.
Palo Alto: 800 sq ft detached on any eligible lot. Larger: 900 sq ft (1 bedroom) or 1,000 sq ft (2+ bedrooms) under added City standards.
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 Palo Alto
How much are the fees for an 800 sq ft ADU in Palo Alto?
Our model of Palo Alto’s official schedules comes to $20,090–$30,394 for a detached 800 sq ft ADU with a 2,000 sq ft main home, compared with $2,000–$12,035 at 750 sq ft.
Does an 800 sq ft ADU pay impact fees in Palo Alto?
Yes: $18,090 in our model, because 800 sq ft is over the 750 sq ft exemption. Fees must be proportional to the main home; a larger house means a smaller share. From 2027, SB 1117 limits them to the 50 sq ft over 750 ($1,131 in our model).
Can Palo Alto 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
- Building permit: the City publishes only a typical range ($2,000–$8,000); the formula is in the FY 2027 Municipal Fee Schedule, which we haven't modeled.
- Utility connection fees (City of Palo Alto Utilities).
- Whether per-sq-ft facility fees are charged on the full ADU area or prorated further (we apply them to the ADU's area).
More
Keep going
Sources
Official sources
Every figure comes from these documents; each line’s quoted text is on the Palo Alto page.
- City of Palo AltoDevelopment Impact and In-Lieu Fees (as of August 17, 2026) (opens in new tab)
- City of Palo AltoJ/ADU Guidebook 2025 (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)