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Can I build an ADU in Orinda, California?

Orinda, Contra Costa County · Ordinances checked 2026-10-05 · Reviewed · 11 cited sections

Allowed with a permit

Yes. ADUs are permitted in every Orinda residential district, and a single-family lot can have one ADU plus one junior ADU (JADU), approved through a ministerial building permit within 60 days with no hearing. A new detached ADU of up to 800 square feet, 16 feet tall and 4 feet from side and rear lines is "streamlined" (no parking required); larger ADUs can be up to 850 sq ft (studio or 1 bedroom) or 1,000 sq ft (2+ bedrooms).

Zones allowedPermitted (P) in RVL, RL, RM and RH districts [1]
Number on a single-family lot1 ADU + 1 JADU [2]
Streamlined detached ADUUp to 800 sq ft, at least 4 ft from side and rear lot lines [3]
Max size (other ADUs)850 sq ft (studio/1 bedroom); 1,000 sq ft (more than 1 bedroom) [4]
Side/rear setback (new ADU)No more than 4 ft [5]
Detached ADU height16 ft (18 ft within 1/2 mile of major transit) [6]
Extra height for matching roof pitch+2 ft [11]
Parking (non-streamlined ADU with a bedroom)1 space, 9 x 19 ft; waived within 1/2 mile of BART or a bus stop and in other cases [7]
Approval timelineMinisterial, within 60 days of a complete application [8]
Impact feesNone for ADUs under 750 sq ft [9]
Short-term rental of streamlined ADUsNot allowed; 30-day minimum [10]

Where and how many

The land use schedule lists accessory dwelling units as permitted (P) in every residential district [1]. On a lot with an existing or proposed single-family home you may have one ADU and one JADU [2]. Orinda's ADU section says that where it is inconsistent with state law, state law governs. The code's detached-ADU fast track requires that the lot have no other ADU; state law allows a converted ADU, a new detached ADU and a JADU on the same single-family lot, so state law may override that limit. Starting January 1, 2027, state law (AB 956) will require cities to approve two new detached ADUs on a single-family lot.

Streamlined ADUs

The code gives a fast track for ADUs that meet state-exempt standards. These include an ADU or JADU created inside the existing house or an existing accessory structure (with up to 150 sq ft added for access), and a new detached ADU that is at least 4 feet from side and rear lot lines and no more than 800 square feet [3]. Streamlined units can be rented only for 30 days or more [10]. The City's ADU page says streamlined ADUs need no added parking space.

All other ADUs

ADUs that don't fit the streamlined categories must meet the zone's objective rules, with state-required limits:

  • Size: up to 850 square feet for a studio or one bedroom, or 1,000 square feet for more than one bedroom [4].
  • Setbacks: none for an ADU within existing space or rebuilt in the same footprint. Otherwise no more than 4 feet from side and rear lot lines [5].
  • Height: an attached ADU follows the house's height limit. A detached ADU is limited to 16 feet, or 18 feet within half a mile of a major transit stop, plus 2 feet for a roof pitch matching the house [11].
  • Parking: one 9-by-19-foot space for an ADU with a bedroom, which can be tandem in the driveway or in setbacks [7]. It's waived within half a mile of BART or a bus stop, for ADUs within the house or an accessory structure, and in other state-listed cases. Garage spaces converted to an ADU don't have to be replaced.

Approval and fees

The Planning Director must act on a complete building permit application within 60 days, ministerially [8]. No impact fees apply to ADUs under 750 square feet [9]. An ADU that doesn't meet the standards can seek a variance, not an exception. The code has no owner-occupancy requirement. ADUs can be rented but not sold separately from the main home. Building permits are issued by Contra Costa County.

See how Orinda compares with 8+ other California towns on accessory dwelling units (adus) →

Next steps

  1. Decide which ADU type fits your lot (inside existing space, new detached up to 800 sq ft, or a larger standard ADU) using OMC §17.3.4 and the City's ADU page.
  2. Ask the Orinda Planning Department (925-253-4210, 22 Orinda Way) to confirm setbacks, creek setbacks and other overlays for your lot; you can book a 30-minute appointment through the ADU page.
  3. Submit a building permit application with site plan and floor plans; you can use a Contra Costa County preapproved ADU plan.
  4. Use the City's ADU fee calculator to estimate impact and plan check fees (no impact fees under 750 sq ft).
  5. Contact the Moraga-Orinda Fire District if you want a separate address for the ADU.

Common questions

Can I build an ADU in Orinda, California?
Yes. ADUs are permitted in every Orinda residential district, and a single-family lot can have one ADU plus one junior ADU, though state law may allow more. Approval is a ministerial building permit decided within 60 days of a complete application, with no hearing.
How big can an ADU be in Orinda, California?
A streamlined new detached ADU can be up to 800 square feet. Other ADUs can be up to 850 square feet for a studio or one bedroom, or 1,000 square feet for more than one bedroom.
How tall can a detached ADU be in Orinda, California?
A detached ADU is limited to 16 feet, or 18 feet within half a mile of a major transit stop, plus 2 feet for a roof pitch matching the house. An attached ADU follows the house's height limit.
Does an ADU need parking in Orinda, California?
It depends. Streamlined ADUs need no added parking space. Other ADUs with a bedroom need one 9-by-19-foot space, waived within half a mile of BART or a bus stop, for ADUs within the house or an accessory structure, and in other state-listed cases.
Can I Airbnb my ADU in Orinda, California?
Not a streamlined one. Streamlined ADUs and JADUs in Orinda can be rented only for 30 days or more. ADUs can be rented but not sold separately from the main home.

California's statewide ADU law

California's ADU law (Gov. Code §§66310–66342, recodified from §65852.2; latest amendments effective January 1, 2026) overrides conflicting city rules, including in charter cities. Cities must approve ADUs ministerially (no hearing) within 60 days of a complete application, or the permit is deemed approved.

What cities cannot require or do:

  • Owner-occupancy for an ADU.
  • A minimum lot size.
  • Side or rear setbacks over 4 feet for a new ADU, or any setback for a converted existing structure.
  • Size, lot coverage or floor-area rules that block an ADU of at least 800 sq ft. Size caps can't be under 850 sq ft (1,000 for 2+ bedrooms).
  • Parking within half a mile walking distance of public transit, or replacement parking for a garage converted to an ADU.
  • Impact fees on ADUs of 750 sq ft or less.

By right on a single-family lot: one converted ADU plus one junior ADU (JADU, up to 500 sq ft inside the house), plus one new detached ADU (up to 800 sq ft, 16 ft tall). Owner-occupancy may be required only for a JADU that shares a bathroom.

Short-term rentals: cities may bar ADU rentals under 30 days, and must for by-right ADUs, JADUs and SB 9 units.

Coming January 1, 2027: AB 956 raises the by-right count to two new detached ADUs per single-family lot.

SB 9 (§§65852.21, 66411.7) allows two homes on a single-family lot, or a split into two lots of at least 1,200 sq ft (with a 3-year owner-occupancy affidavit).

State sources: Gov. Code §66314 (ADU ordinance standards) · Gov. Code §66315 (no owner-occupancy requirement) · Gov. Code §66317 (ministerial review, 60-day deadline) · Gov. Code §66321 (size, setback and height limits on local rules) · Gov. Code §66322 (parking exemptions) · Gov. Code §66323 (by-right ADUs and JADUs) · Gov. Code §66333 (junior ADUs) · Gov. Code §66311.5 (impact fees) · AB 956 (2026), Stats. 2026, ch. 791 · Gov. Code §65852.21 (SB 9 two-unit projects) · Gov. Code §66411.7 (SB 9 urban lot splits) · HCD, Accessory Dwelling Units (ADU Handbook, updated March 2026)

What the ordinance says

Exact text from Orinda's published ordinances. Section numbers are as printed in the source.

  1. OMC §17.3.3(A) Permitted Uses, Municipal Code Title 17 Ch. 17.3 Residential District Base Use Restrictions (17.3.4 ADUs; 17.3.7 Home occupations; 17.3.8 Keeping animals; 17.3.12 Short-term rentals), p. 1
    A use classification followed by the letter "P" is a use that is permitted by right and does not require a use permit.
  2. OMC §17.3.4(B)(2)(b), Municipal Code Title 17 Ch. 17.3 Residential District Base Use Restrictions (17.3.4 ADUs; 17.3.7 Home occupations; 17.3.8 Keeping animals; 17.3.12 Short-term rentals), p. 1
    One ADU and one JADU are permitted per lot with a proposed or existing single-family dwelling if all of the following apply:
  3. OMC §17.3.4(B)(3)(e), Municipal Code Title 17 Ch. 17.3 Residential District Base Use Restrictions (17.3.4 ADUs; 17.3.7 Home occupations; 17.3.8 Keeping animals; 17.3.12 Short-term rentals), p. 1
    The ADU is located at least four feet from the side and rear lot lines, is no greater than eight hundred (800) adjusted square feet in floor area, and has a height in compliance with OMC section
  4. OMC §17.3.4(C)(6)(a), Municipal Code Title 17 Ch. 17.3 Residential District Base Use Restrictions (17.3.4 ADUs; 17.3.7 Home occupations; 17.3.8 Keeping animals; 17.3.12 Short-term rentals), p. 1
    Pursuant to California Government Code Section 66321, the floor area shall not exceed eight hundred and fifty (850) adjusted square feet (studio or one bedroom) or one thousand (1,000) adjusted square feet (more than one bedroom); and
  5. OMC §17.3.4(C)(4)(b)(ii), Municipal Code Title 17 Ch. 17.3 Residential District Base Use Restrictions (17.3.4 ADUs; 17.3.7 Home occupations; 17.3.8 Keeping animals; 17.3.12 Short-term rentals), p. 1
    For all other ADUs, the required setback from side and rear lot lines shall be no more than four feet.
  6. OMC §17.3.4(C)(4)(c)(ii)(B), Municipal Code Title 17 Ch. 17.3 Residential District Base Use Restrictions (17.3.4 ADUs; 17.3.7 Home occupations; 17.3.8 Keeping animals; 17.3.12 Short-term rentals), p. 1
    Detached ADUs on a lot with an existing or proposed single family or multifamily dwelling unit shall be limited to sixteen (16) feet in height.
  7. OMC §17.3.4(C)(4)(e)(i), Municipal Code Title 17 Ch. 17.3 Residential District Base Use Restrictions (17.3.4 ADUs; 17.3.7 Home occupations; 17.3.8 Keeping animals; 17.3.12 Short-term rentals), p. 1
    One all-weather surface, off-street parking space measuring at least nine feet by nineteen (19) feet shall be provided for the ADU.
  8. OMC §17.3.4(D), Municipal Code Title 17 Ch. 17.3 Residential District Base Use Restrictions (17.3.4 ADUs; 17.3.7 Home occupations; 17.3.8 Keeping animals; 17.3.12 Short-term rentals), p. 1
    Within sixty (60) days of receipt of a complete application, the Planning Director shall ministerially process for approval any application for a building permit for an ADU or JADU that meets all the criteria in this Section.
  9. OMC §17.3.4(H) Fees, Municipal Code Title 17 Ch. 17.3 Residential District Base Use Restrictions (17.3.4 ADUs; 17.3.7 Home occupations; 17.3.8 Keeping animals; 17.3.12 Short-term rentals), p. 1
    No impact fees, as defined in California Government Code Section 66324(c)(1), shall be imposed on ADUs smaller than seven hundred and fifty (750) adjusted square feet.
  10. OMC §17.3.4(B)(1)(c), Municipal Code Title 17 Ch. 17.3 Residential District Base Use Restrictions (17.3.4 ADUs; 17.3.7 Home occupations; 17.3.8 Keeping animals; 17.3.12 Short-term rentals), p. 1
    The unit may be rented in full or in part for the purpose of overnight lodging for terms of thirty (30) or more consecutive days, but it shall not be rented for overnight lodging for shorter terms, notwithstanding anything to the contrary in the City's short-term rental regulations
  11. OMC §17.3.4(C)(4)(c)(ii)(C), Municipal Code Title 17 Ch. 17.3 Residential District Base Use Restrictions (17.3.4 ADUs; 17.3.7 Home occupations; 17.3.8 Keeping animals; 17.3.12 Short-term rentals), p. 1
    An additional two feet in height shall be allowed to accommodate a roof pitch on the accessory dwelling unit that is aligned with the roof pitch of the primary dwelling unit.
This page summarizes Orinda's posted ordinances as of 2026-10-05. Ordinances are amended, and individual lots can have overlays, subdivision covenants, or HOA rules that are stricter. Confirm with City of Orinda Code Enforcement / Planning Department, 22 Orinda Way (Planning 925-253-4210); building permits issued by Contra Costa County Building Inspection (925-253-4220) before you build. Spot an error?