Fairfield Zoning and ADU Guide for Homeowners

Last updated November 13, 2026. Reviewed by the Cash Home Buyers CA team.

Fairfield’s municipal code (section 25.20.4.11) treats accessory dwelling unit applications as ministerial, with the city approving or denying a complete application within 60 days, and it allows detached ADUs up to 1,200 square feet. This guide summarizes the city’s ADU and accessory structure rules for homeowners, then explains what they mean when you sell a property with an addition, conversion or backyard unit.

Fairfield ADU rules at a glance

Governing code	Fairfield Municipal Code section 25.20.4.11 (Accessory Dwelling Units) and Table 25-7 (accessory structures)
Review	Ministerial Planning ADU Permit within 60 days of a complete application, plus a building permit
Detached ADU size	Up to 1,200 square feet
Attached ADU size	Up to 50 percent of the primary dwelling or 1,200 square feet
JADU size	220 to 500 square feet, inside the single-family dwelling
Height	16 feet to the roof peak; 25 feet if more than half the floor area is over a garage
Setbacks	4 feet side and rear; none for conversions or same-location replacement
Rental term	30 consecutive days or longer

How approval works

An ADU in Fairfield needs a Planning ADU Permit and a building permit. The Planning review is ministerial, which means staff check the project against the objective standards in the code, and the city acts within 60 days of a complete application.

An ADU that qualifies under Government Code section 65852.2(e)(1) is exempt from the Planning permit and goes straight to the Building Safety Division; see our Fairfield building permits guide for that process. JADUs are also exempt from the Planning ADU permit.

If the property has an illegal addition, the city requires it to be brought into compliance first unless it is exempt. Historic properties must follow the Secretary of the Interior’s guidelines.

Development standards

• Number of units: one detached ADU plus one JADU, or a single ADU, per lot.
• Size: detached up to 1,200 square feet; attached up to 50 percent of the primary dwelling or 1,200 square feet.
• Height: 16 feet to the roof peak, or 25 feet where more than 50 percent of the floor area is over a garage.
• Setbacks: none for a conversion or replacement in the same location; otherwise 4 feet on the side and rear, with front setbacks set by the zone. A detached ADU must be at least 5 feet from the primary dwelling.
• State protection: the code is written so an ADU of 800 square feet, 16 feet tall with 4-foot setbacks can still be built.
• Entry and design: separate exterior access is required, and the design should be similar to the primary home when visible from the street.
• Privacy and lighting: windows within 15 feet of a shared side lot line that face the adjacent side yard must be clerestory style, set 6.5 feet above the finished floor, with exceptions. Exterior lighting must be shielded.
• Foundation and driveways: a permanent foundation is required, and driveways cannot exceed 40 percent of the frontage.
• Parking: no additional parking is required, and garage conversions do not require replacement parking.
• Fire sprinklers: only if required for the primary dwelling.

Junior ADUs

A JADU is a unit of 220 to 500 square feet created within the walls of a single-family home. It must have an efficiency kitchen and may share sanitation facilities with the main house if there is an interior connection. The owner must live on the property in either the main home or the JADU, and a deed restriction must be recorded. A JADU cannot be sold separately.

Rental, sale and fees

ADUs and JADUs must be rented for 30 consecutive days or longer, which rules out short-term rentals, and neither can be sold separately from the primary dwelling. No certificate of occupancy is issued for an ADU before the primary dwelling is complete.

Qualifying ADUs do not require a new utility connection or the associated fees. Impact fees are not charged for ADUs or JADUs under 750 square feet, and larger units are charged proportionally. Adding living space raises assessed value, so review the Prop 13 reassessment guide and the Solano County property tax guide.

Garages and other accessory structures

Converting a garage to an ADU requires no replacement parking. A garage conversion that is not an ADU requires a minimum lot size of 4,500 square feet.

Table 25-7 also sets standards for other accessory structures: a small structure may be up to 7 feet tall and 60 square feet when placed behind a 6-foot fence, while a large accessory structure may be up to 16 feet tall, sit in the rear half of the lot and respect 3-foot setbacks, with rear yard coverage of 20 percent, or 30 percent combined with room additions.

Room additions can reach 35 feet in height with a 15-foot rear setback. Check the exact rules for your zone with Planning before building.

Selling a Fairfield home with an ADU, conversion or unpermitted unit

Because an ADU cannot be sold separately, it adds to the value and marketing of the whole property. A unit built without permits, however, has to be disclosed under the rules in our statewide unpermitted work guide, and rented units bring tenant rules into the sale; see the tenant-occupied sale guide. Before listing:

• Check BUILD for permits covering every room, garage conversion and detached unit.
• Confirm whether the unit meets the 30-day rental rule and whether any deed restriction was recorded.
• Ask Planning what bringing an illegal addition into compliance would require.
• Gather leases, utility records and contractor invoices.
• Compare legalizing, disclosing and selling on the open market, and selling as-is to a cash buyer.

How to sell a house in Fairfield

1. List every structure and unit on the lot and what is permitted.
2. Gather permits, leases and city notices.
3. Request a no-obligation cash offer for the property as it stands.
4. Choose your closing date.
5. Close without legalizing, repairs or showings.

Learn more on our Fairfield cash offer process page.

Frequently asked questions

How big can an ADU be in Fairfield?

Detached ADUs can be up to 1,200 square feet. Attached ADUs can be up to 50 percent of the primary dwelling or 1,200 square feet. JADUs are 220 to 500 square feet.

How long does Fairfield have to review an ADU application?

The code calls for a decision within 60 days of a complete application.

How many ADUs can I have on one lot?

One detached ADU plus one JADU, or a single ADU, per lot.

Do I need extra parking for an ADU?

No additional parking is required, and no replacement parking is needed when a garage is converted.

Can I rent my ADU short term?

No. Fairfield requires rentals of 30 consecutive days or longer.

Can I sell my ADU separately?

No. An ADU or JADU cannot be sold separately from the primary dwelling.

Can I sell my Fairfield house if the ADU or garage conversion is unpermitted?

Yes. You must disclose what you know, and you can sell as-is, including to a cash buyer.

More guides

• We Buy Houses in Fairfield
• We Buy Houses in Solano County
• Solano County Property Tax Guide
• Fairfield Building Permits Guide
• Fairfield Code Enforcement Guide
• Sell My House Fast in Fairfield
• All California Guides

Sources

• City of Fairfield Municipal Code, Title 25, Section 25.20.4.11 (ecode360)

This guide is general information from public sources, not legal advice. Confirm current rules with the city.