800 sq ft ADU · checked Oct 18, 2026
800 sq ft ADU fees in Hayward: $11,272–$21,799, $3,978 more than at 750 sq ft
At 800 sq ft an ADU crosses the 750 sq ft line, so Hayward’s impact fees apply in proportion to the main home: $3,379 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 $211.
750 vs 800
What the extra 50 sq ft changes in Hayward
- Building inspection fee (valuation table): $1,990 at 750 sq ft → $2,090 at 800 sq ft
- Building plan check (100% of inspection fee): $1,990 at 750 sq ft → $2,090 at 800 sq ft
- Planning review (35% of inspection fee): $696 at 750 sq ft → $732 at 800 sq ft
- Fire review (35% of inspection fee): $696 at 750 sq ft → $732 at 800 sq ft
- Technology fee (9% of inspection fee): $179 at 750 sq ft → $188 at 800 sq ft
- Policy planning fee (16% of inspection fee): $318 at 750 sq ft → $334 at 800 sq ft
- Permit issuance fee (35% of inspection fee): $696 at 750 sq ft → $732 at 800 sq ft
- Park impact fee (ADU 750+ sq ft): $0 at 750 sq ft → $3,379 at 800 sq ft (exempt at 750)
- School fee (Hayward Unified; 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 $3,978 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 | |||
| Zoning conformance permit (ADU) | $498 | $498 | $498 |
| Building permit & plan check | |||
| Building inspection fee (valuation table) | Est.$1,990 | Est.$2,090 | Est.$2,090 |
| Building plan check (100% of inspection fee) | $1,990 | $2,090 | $2,090 |
| Planning review (35% of inspection fee) | $696 | $732 | $732 |
| Fire review (35% of inspection fee) | $696 | $732 | $732 |
| Technology fee (9% of inspection fee) | $179 | $188 | $188 |
| Policy planning fee (16% of inspection fee) | $318 | $334 | $334 |
| Permit issuance fee (35% of inspection fee) | $696 | $732 | $732 |
| Housing review fee (ADU) | $158 | $158 | $158 |
| Fire inspection fee | May apply$398 | May apply$398 | May apply$398 |
| Address assignment | $340 | $340 | $340 |
| Impact fees | |||
| Park impact fee (ADU 750+ sq ft) | Exempt | $3,379 | Est.$211 |
| School district fee | |||
| School fee (Hayward Unified; statewide cap shown) | Up to$4,035 | Up to$4,304 | Up to$4,304 |
| Utility connections | |||
| Sewer connection fee (ADU, where applicable) | May apply$5,825 | May apply$5,825 | May apply$5,825 |
| Modeled total | $7,563–$17,821 | $11,272–$21,799 | $8,104–$18,631 |
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 Hayward
How much are the fees for an 800 sq ft ADU in Hayward?
Our model of Hayward’s official schedules comes to $11,272–$21,799 for a detached 800 sq ft ADU with a 2,000 sq ft main home, compared with $7,563–$17,821 at 750 sq ft.
Does an 800 sq ft ADU pay impact fees in Hayward?
Yes: $3,379 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 ($211 in our model).
Can Hayward 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
- We assume type VB (wood-frame) construction for the valuation; type VA's minimum is $211.39/sq ft, and Hayward uses your stated valuation if it's higher.
- State SMIP and building standards fees, solid waste review and landscape inspection aren't included.
- School district rate not captured; shown at the statewide cap.
- Local size, height and parking rules not captured yet; the state minimums apply.
More
Keep going
Sources
Official sources
Every figure comes from these documents; each line’s quoted text is on the Hayward page.
- City of HaywardAdopted Master Fee Schedule, Fiscal Year 2026-2027 (effective July 1, 2026) (opens in new tab)
- City of HaywardThe Accessory Dwelling Unit (ADU) Process (handout) (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)