Solano County

Suisun City ADU rules

Research summary of what we found for City of Suisun City in Solano County. Not a determination for a specific lot.

Last checked November 3, 2026.

City or county ADU page

Suisun City Planning department. No ADU-specific page was found.

How big can an ADU be in Suisun City?

Maximum size
Besides the 800 sq ft units allowed under state law, a detached ADU on a single-family lot (RL and RM zones) may be up to 850 sq ft with one bedroom or less, or 1,000 sq ft with more than one bedroom. Sizes count interior livable space. A JADU may be up to 500 sq ft. One ADU and one JADU are allowed under these rules on a lot with a single-family home.
Source: Suisun City Municipal Code § 18.30.170 Accessory dwelling units and junior accessory dwelling units, and Table 18.31.01 (Ord. 825, April 21, 2026) (Municode), § 18.30.170(B)(3)(a), (d); Table 18.31.01, accessed 2026-11-03.

ADU setbacks in Suisun City

Setbacks
New ADUs need at least 4 ft side and rear setbacks. The front setback is waived if it would block a unit on the site. A detached ADU built under the local (larger) rules must be in the rear half of the lot, unless that would block it, in which case it may go in the front half.
Source: Suisun City Municipal Code § 18.30.170 Accessory dwelling units and junior accessory dwelling units, and Table 18.31.01 (Ord. 825, April 21, 2026) (Municode), § 18.30.170(A)(3)(b), (B)(3)(b)-(c); Table 18.31.01, accessed 2026-11-03.

What we found for Suisun City

What we have for this place. Where a local figure is stricter than the California state baseline, both are shown.

Local ADU rules
Suisun City's ADU rules are in Municipal Code Section 18.30.170 and Table 18.31.01, replaced in full by Ordinance 825 (introduced April 7, 2026, adopted April 21, 2026, in effect 30 days after adoption). The update followed a December 5, 2025 letter from the state housing department. ADU and JADU permits are reviewed without a hearing. The City decides whether an application is complete within 15 business days and acts on a complete application within 60 days.
Source: Suisun City Municipal Code § 18.30.170 Accessory dwelling units and junior accessory dwelling units, and Table 18.31.01 (Ord. 825, April 21, 2026) (Municode), § 18.30.170(A)(1); Table 18.31.01 note 1 (packet pages 100-108), accessed 2026-11-03.

ADU types under state law
These units are allowed with only state standards: on a single-family lot, one JADU (up to 500 sq ft) plus one ADU inside the home or an existing accessory structure (up to 150 sq ft may be added for entry and exit), and one new detached ADU up to 800 sq ft and 16 ft with 4 ft side and rear setbacks. On multifamily lots: converted ADUs in non-livable space (at least one, up to 25% of the units), and up to eight detached ADUs (not more than the existing units) or two with a proposed multifamily building, each up to 800 sq ft with 4 ft side and rear setbacks.
Source: Suisun City Municipal Code § 18.30.170 Accessory dwelling units and junior accessory dwelling units, and Table 18.31.01 (Ord. 825, April 21, 2026) (Municode), § 18.30.170(A)(3); Table 18.31.01, accessed 2026-11-03.

Height
A detached ADU may be 16 ft. It may be 18 ft within a half mile of a major transit stop (the Suisun-Fairfield Amtrak station), on a lot with an existing or proposed multistory multifamily building, and for 800 sq ft units in the RH1, RH2 and RMU zones. A detached ADU may also match the height of a main home taller than 16 ft.
Source: Suisun City Municipal Code § 18.30.170 Accessory dwelling units and junior accessory dwelling units, and Table 18.31.01 (Ord. 825, April 21, 2026) (Municode), § 18.04.010 (major transit stop); § 18.30.170(A)(3)(b), (d); Table 18.31.01 note 3, accessed 2026-11-03.

Parking
One space per ADU or per bedroom, whichever is less. It may be tandem and in setback areas. No space is needed within a half mile walk of public transit, in a historic district, for an ADU inside the home or an existing accessory structure, where on-street permits are required but not offered, or within one block of a car share vehicle. A garage, carport or covered parking removed or converted for an ADU does not have to be replaced.
Source: Suisun City Municipal Code § 18.30.170 Accessory dwelling units and junior accessory dwelling units, and Table 18.31.01 (Ord. 825, April 21, 2026) (Municode), § 18.30.170(A)(2)(a), (B)(3)(f); Table 18.31.01 note 4, accessed 2026-11-03.

Junior ADUs
A JADU may be up to 500 sq ft of interior livable space inside a single-family home, with its own exterior entrance. It may have its own bathroom or share the home's. The owner must live in the home or the JADU only when the JADU does not have its own bathroom.
Source: Suisun City Municipal Code § 18.30.170 Accessory dwelling units and junior accessory dwelling units, and Table 18.31.01 (Ord. 825, April 21, 2026) (Municode), § 18.04.010 (JADU); § 18.30.170(A)(3)(a), (B)(3)(d)-(e), accessed 2026-11-03.

Fees, sprinklers and renting
No impact fees other than school fees for an ADU or JADU with 750 sq ft or less of interior livable space. School fees may apply above 500 sq ft. Fire sprinklers are needed only if the main home needs them. A permit is not tied to fixing existing nonconforming conditions. ADUs and JADUs must be rented for more than 30 days.
Source: Suisun City Municipal Code § 18.30.170 Accessory dwelling units and junior accessory dwelling units, and Table 18.31.01 (Ord. 825, April 21, 2026) (Municode), § 18.30.170(A)(2)(b)-(d), (B)(2), (B)(3)(g), accessed 2026-11-03.

State housing department (HCD) review
On December 5, 2025, HCD sent Suisun City a technical assistance letter saying the ADU ordinance it had on file was from 2020 and might be out of date, and listing state law changes since then. The City answered with Ordinance 825 (April 2026). HCD has not posted a review of the new ordinance that we found.
Source: HCD letter of technical assistance to Suisun City, December 5, 2025 (attachment to the April 7, 2026 City Council agenda packet), Letter of December 5, 2025 (packet page 109 and following), accessed 2026-11-03.

California state rules

The statewide baseline recorded from state law and the HCD ADU Handbook.

Detached size cap described in state law
1,200 sq ft. From Government Code section 66314.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.

Side and rear setback cap for a new ADU
4 ft. From Government Code section 66314, which describes a cap on side and rear setbacks for a new ADU.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.

Setback for a conversion of an existing structure
No additional setback, from Government Code section 66314 for a conversion of an existing structure.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.

Minimum lot size
A city may not impose a minimum lot size for an ADU, from Government Code section 66314.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.

Minimum unit the handbook says cities must allow
At least an 800 sq ft ADU with 4 ft side and rear setbacks. The HCD ADU Handbook (updated March 2026) describes this under section 66321(b)(3).
Source: HCD ADU Handbook, 66321(b)(3); handbook updated March 2026, accessed 2026-10-16.

Detached height described in the handbook
16 ft, or 18 ft or 20 ft in some cases. The HCD ADU Handbook (updated March 2026) describes this under section 66321(b)(4).
Source: HCD ADU Handbook, 66321(b)(4); handbook updated March 2026, accessed 2026-10-16.

Permit decision deadline
60 days. From Government Code section 66317(a)(3): the permitting agency must decide on (approve or deny) a completed ADU application within 60 days when an existing single-family or multifamily dwelling is on the lot. Section 66317(a)(1) says the application is considered ministerially, without discretionary review or a hearing.
Source: California Government Code section 66317, 66317(a)(1), (a)(3), accessed 2026-10-17.

Owner-occupancy requirement
None. From Government Code section 66315: a local agency may not impose an owner-occupancy requirement on an ADU. It may require that the property be used for rentals of terms 30 days or longer. The HCD ADU Handbook (updated March 2026) describes the same rule.
Source: California Government Code section 66315, 66315; HCD ADU Handbook updated March 2026, accessed 2026-10-17.

Parking near public transit
No parking standards within one-half mile walking distance of public transit. From Government Code section 66322(a)(1). Section 66322(a) lists several other cases where parking standards may not be imposed.
Source: California Government Code section 66322, 66322(a), accessed 2026-10-17.

Ministerial categories
The HCD ADU Handbook (updated March 2026) states that Government Code section 66323 sets four ministerial categories. What we have does not restate those four categories.
Source: HCD ADU Handbook, 66323; handbook updated March 2026, accessed 2026-10-16.

Fire Hazard Severity Zones
If your lot is in a Fire Hazard Severity Zone, the CAL FIRE Office of the State Fire Marshal says in Information Bulletin 25-004 (issued March 3, 2025): “Fire Hazard Severity Zones (FHSZs) should not restrict the development of Accessory Dwelling Units (ADUs). However, additional building standards may be necessary, including but not limited to California Fire Code Chapter 49 and California Building Code Chapter 7A.” State ADU law does not itself bar an ADU there. A city or county may still apply its building code, including wildfire-resistant construction (Gov. Code 66314(d)(8)); require side and rear setbacks “sufficient for fire and safety” for a unit converted under 66323(a)(1); and decline parking in setbacks on specific fire and life safety findings (66314(d)(10)(B)). It may also consider public safety when it designates where ADUs may be permitted (66314(a)). Sprinklers can't be required in an ADU or JADU if the primary residence doesn't need them (66314(d)(12), 66323(d)). Some cities and counties still apply their own fire-zone limits. Where this summary has one, it is listed with the local rules. This summary does not look up your lot. Check the CAL FIRE Fire Hazard Severity Zone map viewer linked from the State Fire Marshal's Fire Hazard Severity Zones page: https://experience.arcgis.com/experience/5065c998b4b0462f9ec3c6c226c610a9
Source: CAL FIRE Office of the State Fire Marshal Information Bulletin 25-004, page 4, issued March 3, 2025; Gov. Code 66314, 66323, accessed 2026-10-20.

Starting January 1, 2027: two detached ADUs
Starting January 1, 2027, AB 956 (Chapter 791, Statutes of 2026) raises from one to two the number of new detached ADUs a city or county must allow, without discretionary review, on a lot with a proposed or existing single-family home (Gov. Code 66323(a)). Each may be held to 800 sq ft, 4 ft side and rear setbacks and the state height limits. The city or county does not have to also allow a JADU on a lot where two new detached ADUs have been built. AB 956 also makes HOA and deed rules that effectively prohibit or unreasonably restrict an ADU or JADU void on any lot zoned to allow a single-family home, not only lots zoned for single-family use (Civil Code 4751 and 714.3).
Source: AB 956 (2025-2026), Chapter 791, Statutes of 2026, Gov. Code 66323; Civil Code 714.3, 4751; signed September 29, 2026, accessed 2026-11-03.

Starting January 1, 2027: impact fees above 750 sq ft
No impact fee may be charged on an ADU of 750 sq ft or less, or a JADU of 500 sq ft or less (Gov. Code 66311.5(c)). Starting January 1, 2027, SB 1117 (Chapter 809, Statutes of 2026) changes how fees are figured for larger ADUs: for up to two ADUs on a lot, the proportional impact fee is charged only on the interior livable space above 750 sq ft. On a lot with more than two ADUs, the fee stays proportional to the whole ADU. Utility connection fees and capacity charges are not changed.
Source: SB 1117 (2025-2026), Chapter 809, Statutes of 2026, Gov. Code 66311.5(c); signed September 29, 2026, accessed 2026-11-03.

State baseline on the directory → · State ADU rules on the homepage →

ADU rules near Suisun City

Unincorporated Solano County
Vacaville · about 8 miles
American Canyon · about 14 miles
Benicia · about 14 miles
Napa · about 16 miles

Can I build an ADU in Suisun City?

State law sets a baseline for ADUs in Suisun City, and what we found locally is listed on this page. Whether a specific lot can add an ADU depends on zoning, utilities, and other site facts this page does not measure. Confirm with the City of Suisun City Development Services Department (Planning), or run a free address summary.

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