Town Permit Guide

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Can I build an ADU in Piedmont, California?

Piedmont, Alameda County · Ordinances checked 2026-10-05 · Reviewed · 12 cited sections

Allowed with a permit

Yes. ADUs are a permitted use in Piedmont's single-family Zone A, approved ministerially (no hearing) by the Planning Director within 60 days. A detached ADU can be up to 850 sq ft (1,000 sq ft with more than one bedroom) and 18 feet tall, at least 4 feet from side and rear lot lines, with no parking required.

Allowed in single-family Zone AYes, permitted use [1]
ApprovalADU permit plus building permit [2]
ReviewMinisterial, no notice or hearing; decision within 60 days [3]
Detached ADU max size850 sq ft; 1,000 sq ft with 2+ bedrooms [5]
Attached ADU max size50% of existing living area, up to 850/1,000 sq ft (800 sq ft always allowed) [4]
Minimum ADU size150 sq ft [5]
Detached ADU height18 ft (+2 ft to match main roof pitch) [6]
Side/rear setback (new ADU)4 feet; none for conversions [7]
ParkingNone required [8]
Junior ADUUp to 500 sq ft inside the house; one per lot [9]
Owner-occupancyOnly for a JADU that shares a bathroom [10]
Short-term rental of ADUNot allowed [11]

Where and what kind

An accessory dwelling unit is a permitted use in Zone A, Piedmont's single-family zone [1], and the ADU rules in Division 17.38 also apply in Zones C, D and E. You need an ADU permit to build an ADU or junior ADU, or to change an existing one's exterior, size or height [2]. The Director reviews applications ministerially against the standards in section 17.38.060 and must decide within 60 days of a complete application, without notice or a public hearing [3].

Size and height

  • Attached ADU: up to 50% of the existing living area, capped at 850 sq ft (1,000 sq ft with more than one bedroom); 800 sq ft is allowed even if 50% would be smaller [4].
  • Detached ADU: up to 850 sq ft, or 1,000 sq ft with more than one bedroom; minimum 150 sq ft [5]. The Director can grant a size exception up to 1,200 sq ft under section 17.38.070 with conditions.
  • Height: 18 feet for a detached ADU, plus 2 feet if the roof pitch matches the main house [6]. Attached ADUs are capped at 25 feet or the zone limit.

Setbacks, parking and coverage

A new ADU needs only 4 feet from side and rear lot lines, and a conversion of an existing structure needs no setback [7]. ADUs of 800 sq ft or less may go in the street yard setback and are exempt from lot coverage, landscaping and floor-area limits. Parking isn't required for an ADU, since the code notes all Piedmont properties are within half a mile of transit [8].

Junior ADUs and occupancy

A junior ADU is up to 500 sq ft within the house with its own entrance [9]. If it shares a bathroom with the house, the owner must live on the site [10]. The code has no owner-occupancy requirement for a regular ADU.

Rentals and new homes

ADUs may not be used as short-term rentals (under 30 days) [11]. On lots over 5,000 sq ft, an ADU is required when a new house is built on a vacant lot or a house is demolished and rebuilt [12].

State law

Piedmont's standards largely track state ADU law. Starting January 1, 2027, state law (AB 956) allows two new detached ADUs per single-family lot, which goes beyond the one new detached ADU that section 17.38.060(D) currently requires the city to approve; that state rule may override Piedmont's code once it takes effect.

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

Next steps

  1. Check the standards in City Code section 17.38.060 (size, height, 4-ft setbacks) against your lot and plans.
  2. Submit an ADU permit application and fee to the Piedmont Planning & Building Department, 120 Vista Avenue, (510) 420-3050; the Director decides within 60 days without a hearing.
  3. Apply for a building permit for construction; a JADU can't be occupied until it passes final inspection and gets a certificate of occupancy.
  4. If you'll rent the unit, plan on leases of 30 days or more and register for the City's business license tax on rental property.

Common questions

Are ADUs allowed in Piedmont, California?
Yes. ADUs are a permitted use in Piedmont's single-family Zone A, approved ministerially (no hearing) by the Planning Director within 60 days.
How big can an ADU be in Piedmont, California?
A detached ADU can be up to 850 sq ft (1,000 sq ft with more than one bedroom) and 18 feet tall, at least 4 feet from side and rear lot lines.
Does an ADU need parking in Piedmont, California?
No. No parking is required.
Can I rent my ADU short term in Piedmont, California?
No. Short-term rental of an ADU is not allowed.

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 Piedmont's published ordinances. Section numbers are as printed in the source.

  1. Sec. 17.20.020(C) Permitted uses (Zone A), City Code Chapter 17 Planning and Land Use (zoning; through Ord. 791 N.S., 04/2026), p. 10
    C. Accessory dwelling unit, subject to division 17.38.
  2. Sec. 17.38.040(A) Accessory dwelling unit permit, City Code Chapter 17 Planning and Land Use (zoning; through Ord. 791 N.S., 04/2026), p. 49
    An accessory dwelling unit permit is required for construction of an accessory dwelling unit or junior accessory dwelling unit or the modification of exterior features, size, or height of an existing accessory dwelling unit or junior accessory dwelling unit.
  3. Sec. 17.38.050(B) Ministerial review, City Code Chapter 17 Planning and Land Use (zoning; through Ord. 791 N.S., 04/2026), p. 50
    The Director shall review each application ministerially to determine if the development standards in section 17.38.060 are met, and shall within 60 days of a completed ap plication approve or deny the application
  4. Sec. 17.38.060(B)(1) Size, City Code Chapter 17 Planning and Land Use (zoning; through Ord. 791 N.S., 04/2026), p. 50
    An attached accessory dwelling unit may not exceed 50% of the existing living area up to a maximum of 850 square feet, or 1,000 square feet if the accessory dwelling unit will include more than one bedroom
  5. Sec. 17.38.060(B)(1) Size, City Code Chapter 17 Planning and Land Use (zoning; through Ord. 791 N.S., 04/2026), p. 50
    A detached accessory dwelling unit may not exceed 850 square feet, or 1,000 square feet if the accessory dwelling unit will include more than one bedroom. The minimum floor area for an accessory dwelling unit shall be 150 square feet.
  6. Sec. 17.38.060(B)(4) Building Height, City Code Chapter 17 Planning and Land Use (zoning; through Ord. 791 N.S., 04/2026), p. 51
    A detached accessory dwelling unit shall not exceed a building height of 18 feet. An additional height of two feet for a detached accessory dwelling unit shall be allowed to accommodate a roof pitch that is aligned with the roof pitch of the primary dwelling unit.
  7. Sec. 17.38.060(B)(6)(b) Side and Rear Setbacks, City Code Chapter 17 Planning and Land Use (zoning; through Ord. 791 N.S., 04/2026), p. 51
    If an accessory dwelling unit is not converted from an existing structure, the minimum setback is four feet from the side and rear lot line.
  8. Sec. 17.30.010(B)(1) Parking table, note *, City Code Chapter 17 Planning and Land Use (zoning; through Ord. 791 N.S., 04/2026), p. 30
    Under Government Code section 65852.2, the city may not require parking for an accessory dwelling unit located within 1/2 mile of public transit, and all Piedmont properties are within 1/2 mile.
  9. Sec. 17.38.020 Definitions (Junior accessory dwelling unit), City Code Chapter 17 Planning and Land Use (zoning; through Ord. 791 N.S., 04/2026), p. 48
    Junior accessory dwelling unit means a unit that is no more than 500 square feet in size and contained within a single-family residence, with a separate entrance.
  10. Sec. 17.38.060(C)(3)(c) JADU use restrictions, City Code Chapter 17 Planning and Land Use (zoning; through Ord. 791 N.S., 04/2026), p. 55
    If a junior accessory dwelling unit has shared sanitation facilities with the existing structure, the site's owner shall not allow occupancy of the junior accessory dwelling unit by a tenant for any reason, with or without payment of rent, unless the site owner maintains occupancy on the site as their primary residence.
  11. Sec. 17.40.030(A) Short-term rental, Applicability, City Code Chapter 17 Planning and Land Use (zoning; through Ord. 791 N.S., 04/2026), p. 62
    It may not be located in an accessory dwelling unit (permitted or unintended), a multi-family dwelling unit, or a dwelling unit created under division 17.54.
  12. Sec. 17.20.040(C) Zone A regulations, City Code Chapter 17 Planning and Land Use (zoning; through Ord. 791 N.S., 04/2026), p. 12
    C. For lots that are larger than 5,000 square feet, an ADU shall be constructed:
This page summarizes Piedmont'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 Piedmont Planning & Building Department, 120 Vista Avenue ((510) 420-3050) before you build. Spot an error?