Compare · checked Oct 18, 2026

San Mateo vs Redwood City ADU fees: San Mateo $8,702–$20,090 vs Redwood City $5,170 in modeled fees for 1,000 sq ft, before building permits in both

Modeled from each place’s official fee schedules for a detached ADU next to a 2,000 sq ft main home (example assumption), law in force today. Ranges count fees that always apply (low) and fees that may apply (high). Not like for like: San Mateo: Totals leave out valuation-based building fees. Redwood City: Totals leave out new adu base building fee at some sizes.

Modeled fee totals by ADU size

	San Mateo	Redwood City	Lower
499 sq ft	$5,761	$4,661	Redwood City by $1,100
750 sq ft	$7,234–$11,269	$9,199	Redwood City by $2,070
1,000 sq ft	$8,702–$20,090	$5,170	Redwood City by $14,920
1,200 sq ft	$9,876–$23,542	$6,204	Redwood City by $17,338

Where the money goes at 1,000 sq ft

	San Mateo	Redwood City
Building permit & plan check	Needs valuation	Needs valuation
Impact fees	$0–$6,008	$0
School district fee	$0–$5,380	$5,170
Utility connections	$5,870	–
Impact fees under SB 1117 (from 2027)	$1,502	$0
ADU permits issued, 2025	151	63

Line-by-line figures with the quoted source text: San Mateo · Redwood City. Permits: HCD Annual Progress Report data.

Rules side by side

	San Mateo	Redwood City
Maximum size	State floor: cities must allow at least 850 sq ft (1,000 sq ft with 2+ bedrooms); detached ADUs can be capped at 1,200 sq ft.	Up to 850 sq ft for a one-bedroom ADU, or 1,000 sq ft with more than one bedroom.
Height	State floor: 16 ft detached (18 ft near transit or on a multifamily lot, +2 ft for roof pitch); 25 ft attached.	State floor: 16 ft detached (18 ft near transit or on a multifamily lot, +2 ft for roof pitch); 25 ft attached.
Setbacks	State limit: no more than 4 ft side and rear.	State limit: no more than 4 ft side and rear.
Parking	State limit: at most 1 space per ADU or bedroom, and none within ½ mile of transit and in other cases.	State limit: at most 1 space per ADU or bedroom, and none within ½ mile of transit and in other cases.
Owner occupancy	State law: cities can't require the owner to live on site for an ADU (JADUs: owner on site if sanitation is shared).	State law: cities can't require the owner to live on site for an ADU (JADUs: owner on site if sanitation is shared).
Pre-approved plans	State law: every city must run a program to pre-approve ADU plans (Gov. Code 65852.27).	State law: every city must run a program to pre-approve ADU plans (Gov. Code 65852.27).

Grey text is the state floor where we haven’t captured the local rule yet.

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FAQ

San Mateo vs Redwood City: questions

Are ADU fees higher in San Mateo or Redwood City?

For a detached 1,000 sq ft ADU with a 2,000 sq ft main home, our model of the official schedules gives San Mateo $8,702–$20,090 and Redwood City $5,170. San Mateo: Totals leave out valuation-based building fees. Redwood City: Totals leave out new adu base building fee at some sizes.

Which charges more impact fees on an ADU, San Mateo or Redwood City?

At 1,000 sq ft: San Mateo $6,008, Redwood City $0 (proportional to a 2,000 sq ft house). Neither can charge impact fees at 750 sq ft or less. From 2027, SB 1117 limits them to the area over 750 sq ft: $1,502 and $0 in our model.

What does a 750 sq ft ADU cost in fees in each?

San Mateo: $7,234–$11,269. Redwood City: $9,199. At 750 sq ft or less, state law bars impact fees in both.

By project type

Specific projects

800 sq ft ADU fees in Redwood City

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