Concord Zoning and ADU Guide for Homeowners

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

Concord regulates accessory dwelling units (ADUs) through its Development Code, Section 18.200.180, and offers free pre-approved ADU plans to speed up permitting. This guide summarizes what Concord publishes about ADUs, junior ADUs (JADUs) and SB 9 lot splits, and what those rules can mean when you own or sell a Concord home with a backyard unit, a garage conversion or an unpermitted addition.

Concord ADU rules at a glance

Where the rules live	Concord Development Code, Section 18.200.180 (ADUs); district standards in Table 18.30.030
Maximum ADU size, lot 12,000 sq ft or less	1,000 sq ft, plus up to 230 sq ft of attached garage, carport or porch
Maximum ADU size, lot over 12,000 sq ft	1,200 sq ft, plus up to 460 sq ft of attached garage, carport or porch
Attached ADU limit	No more than 50% of the existing primary dwelling
JADU size	Up to 500 sq ft, within the principal residence
Parking, new detached ADU	One uncovered driveway space, per the city FAQ; exemptions exist
Owner occupancy	Required for a lot with a JADU; not required for an ADU alone
Rentals	ADUs must be rented for at least 30 days
Separate sale	An ADU cannot be sold separately from the principal residence
Free pre-approved plans	Offered by the city to speed permitting

How big can a Concord ADU be?

Concord’s ADU FAQ ties maximum size to your net lot area. On a lot of 12,000 square feet or less, an ADU can be up to 1,000 square feet, and the unit may also have an attached garage, carport or porch of up to 230 square feet on top of that.

On a lot of 12,001 square feet or more, the limit rises to 1,200 square feet with up to 460 square feet of attached garage, carport or porch. An attached ADU cannot exceed 50 percent of the existing primary dwelling.

A junior ADU is capped at 500 square feet and must be created within the walls of the principal residence.

The city’s FAQ notes that, in some circumstances, a lot may be allowed both an ADU and a JADU. Size, setbacks and placement depend on your parcel, so the city suggests meeting with a planner to see where a unit can go, how large it can be and how to meet setback and parking requirements.

Parking, owner occupancy and rentals

For a new detached ADU, the city FAQ says one uncovered driveway space is required, and the city publishes a separate document on parking requirements and exemptions. Owner occupancy works differently for the two unit types.

A lot with a JADU requires the owner to live in the principal residence, the JADU or an ADU on the same lot. A standalone ADU has no owner-occupancy requirement. Any ADU rental must be for at least 30 days, which rules out nightly short-term rentals.

A JADU with an internal connection to the main house does not need its own address, though one can be requested.

Two other points from the FAQ matter to future buyers. An ADU cannot be sold or conveyed separately from the main home, so you sell the property as a whole. And under state law, cities cannot charge impact fees on ADUs smaller than 750 square feet, though you still pay plan check and permit fees to the Building Division, which the city says are often a few thousand dollars.

Pre-approved and custom ADU plans

Concord has two routes. The city offers free, standardized pre-approved ADU plans meant to make permitting faster and cheaper, and it also lists pre-approved plans from outside designers that comply with its objective design standards.

If you want something different, the custom-designed ADU process starts with a planner meeting to confirm location, allowable size, setbacks and parking. After planning review, construction plans go through the Building Division, which is covered in our Concord building permits guide.

SB 9 lot splits and duplexes in Concord

State law SB 9 allows certain single-family parcels to add a second home or be split into two lots. Concord’s SB 9 handout says it applies in the Residential Single-Family (RS) and Rural Residential (RR) districts. A single parcel can have two single-family dwellings plus an ADU, for three units total, and ADUs and JADUs count toward the unit total. Key points from the handout:

• Setbacks. No setback is needed for an existing structure or one rebuilt in the same place and size. New units need at least four feet from side and rear lot lines and must meet the regular front setback for the district.
• Parking. One covered space per unit, unless the parcel is within one-half mile walking distance of a BART station or Clayton Road, or within one block of a car-share vehicle. Tandem parking is allowed.
• Lot splits. Each new parcel must be at least 1,200 square feet and at least 40 percent of the original parcel area, and the owner must sign an affidavit of intent to occupy one of the units as a principal residence for at least three years after approval of an urban lot split.
• Exclusions. Parcels with a designated historic resource, or projects that would demolish or alter deed-restricted affordable or rent-controlled housing or housing occupied by a tenant in the last three years, are not eligible. If a tenant lived on site in the last three years, no more than 25 percent of existing exterior walls may be demolished.
• Process and fees. The steps run from an optional pre-application meeting and an eligibility determination request through online submittal, staff review and a determination letter. The city asks for a $3,000 deposit, and staff time is charged against it.

How to check your property’s zoning

Setbacks, lot coverage and height depend on your zoning district, which appear in Table 18.30.030 of the Development Code. The city’s ADU page points owners to its zoning lookup, and the Permit Center can confirm your district. Always confirm the district before you rely on any rule above, because some standards differ for RS, RR and multifamily lots.

Selling a Concord home with an ADU or unpermitted addition

A permitted ADU can add value, but buyers and lenders usually ask for proof that it was permitted and finaled. A converted garage, back-house or room addition without permits can complicate financing and appraisal. Our statewide guide to selling as-is with unpermitted work covers disclosure and your options, and the seller closing costs guide shows what to expect at closing.

• Collect permits, final inspection records and plans for any ADU, conversion or addition.
• Check whether the unit meets current size, parking and rental rules, including the 30-day minimum rental term.
• Remember an ADU cannot be sold separately, so the whole property is what you list or sell.
• If the work was never permitted, compare the cost of permits and corrections with selling as-is.
• Disclose known issues honestly on your transfer disclosures.

How to sell a house in Concord

1. Gather any ADU permits, plans and zoning information you have.
2. Note any unpermitted conversions or open city issues.
3. Request a no-obligation cash offer for the property as it stands.
4. Choose your closing date.
5. Close with no repairs, permits or showings required.

Our local pages cover Concord sales in more detail, including selling as-is and selling fast, and the Concord code enforcement guide explains what happens when the city flags a violation.

Frequently asked questions

How large can an ADU be in Concord?

Up to 1,000 square feet on lots of 12,000 square feet or less and up to 1,200 square feet on larger lots, with a separate allowance for an attached garage, carport or porch. Attached ADUs cannot exceed 50 percent of the primary dwelling.

Do I have to live on the property if I have an ADU?

Not for an ADU alone. A lot with a junior ADU requires the owner to live in the main house, the JADU or an ADU on the lot.

Can I use a Concord ADU as a short-term rental?

No. The city FAQ says ADU rentals must be for at least 30 days.

Can an ADU be sold separately?

No. It cannot be sold or conveyed separately from the principal residence.

Does Concord offer pre-approved ADU plans?

Yes. The city offers free pre-approved plans and also lists pre-approved plans from outside designers.

Where does SB 9 apply in Concord?

The city’s handout says the Residential Single-Family (RS) and Rural Residential (RR) districts, subject to eligibility limits on historic properties, tenant-occupied housing and demolition.

Can I sell a Concord house with an unpermitted ADU?

Yes. You can disclose the condition and sell as-is, including to a cash buyer.

More guides

• We Buy Houses in Concord
• We Buy Houses in Contra Costa County
• Contra Costa County Property Tax Guide
• Concord Building Permits Guide
• Concord Code Enforcement Guide
• All California Guides

Sources

• City of Concord: Accessory Dwelling Units
• City of Concord: ADU FAQs
• City of Concord: SB 9 Summary and Application Process

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