Please see the City’s full Accessory Dwelling Unit ordinance for detailed and specific requirements.

Number of ADUs that can be Built



ADUs Allowed

Property with a proposed or existing single-family dwelling

1 ADU and 1 JADU


Property with a proposed multi-family dwelling

At least 1 ADU that is attached, detached, or a conversion of space in an existing dwelling

Property with an existing multi-family dwelling

At least 1 conversion ADU within the dwelling’s non-livable space (e.g., storage rooms, boiler rooms, passageways, attics, basements, or garages), or up to 25 percent of the existing number of multi-family dwelling units (whichever is greater)




Not more than 2 detached ADUs (including the conversion of an existing accessory structure to an ADU), that meets specified building code and health and safety requirements.




1 attached ADU




Type of Accessory Dwelling Unit

Required Parking




1 off-street parking space

ADU created through the conversion or demolition of a garage, carport, or covered parking structure (including replacement of existing parking spaces that are removed to accommodate the ADU).


ADU located within one-half mile walking distance of a public transit station/stop or if the ADU is part of the principal dwelling (except for additions).



Setback Requirements by Type of ADU


Type of Accessory Dwelling Unit

Required Setback

Conversion of existing space within a single-family principal dwelling or non-livable space within a multifamily principal dwelling

No additional setback, but distance must be sufficient for fire and safety.

Conversion of existing accessory structure or garage (single-family or multifamily principal dwelling)

No additional setback, but distance must be sufficient for fire and safety.

New addition to an existing single-family or multifamily principal dwelling

4-foot interior side and rear setback.*

New detached building (single-family or multifamily principal dwelling)

4-foot interior side and rear setback.*

* Front and exterior (corner) side setbacks of the applicable zoning district must be met, unless the ADU is 800 square feet or less and cannot feasibly be constructed elsewhere on the lot.


  • A detached ADU may measure up to 16 feet tall; however, a height of 18 feet is allowed under the following circumstances:
    1. If necessary to match the roof pitch of the main dwelling (plus an additional two feet; up to 20 feet may be allowed).
    2. If the property is within one-half mile of a BART station or Clayton Road.
    3. If the property has a multifamily, multi-story dwelling.
  • An attached ADU may measure up to 25 feet tall, provided it does not exceed two stories
  • See Section 18.200.180(E)(6) for additional height exceptions 


  • Exempt ADUs are exempt from design standards (see “Exempt ADUs” below for further details).
  • Nonexempt ADUs shall be comparable to the single-family principal dwelling in roof pitch and form, and siding materials and colors, unless approved through the City’s Design and Site Review process.
  • Attached ADUs shall have a separate entrance that is not located on the same side or facing in the same direction as the entrance for the single-family principal dwelling or an exterior staircase that is visible from the street or pubic right-of-way. 

Exempt ADUs

The City of Concord, in conformance with State law, exempts certain ADUs from many local development standards. 

A detached ADU is exempt if it is:

  • 800 square feet or less; and
  • In compliance with the height limits stated above; and
  • Set back 4 feet or more from the side and rear property lines

Conversion of an existing detached accessory structure to an ADU is exempt if it:

  • Does not add more than 150 square feet of additional floor area for ingress and egress.

Conversion of existing space to an ADU that is attached to the principal dwelling is exempt if it is:

  • Located entirely within an existing single-family dwelling (including garages); or
  • Located within the non-livable space of an existing multifamily dwelling structure and up to 25 percent of the number of existing multifamily dwelling units; or
  • Located within a legally constructed addition to an existing single- or multifamily dwelling.

Prefab and Pre-designed ADUs

There are a variety of companies that can help you build an ADU, including companies that meet the requirements of an exempt ADU. 
If the ADU is not exempt, then it will need to meet Concord’s design requirements (CDC Section 18.200.180.E). In general, the exterior appearance of the accessory dwelling unit shall be comparable to the principal dwelling in roof pitch and form, and siding materials and colors. 

Short-term Rentals

ADUs and JADUs cannot be rented for fewer than 30 consecutive calendar days.