California ADU rules · Alameda County
Can I Build an ADU in Piedmont?
Yes — you can build an ADU in Piedmont. California's statewide ADU law requires every city, including Piedmont, to approve a qualifying accessory dwelling unit by right, plus a junior ADU (JADU) on a single-family lot. What varies city to city are the local specifics below.
Can you build one?
ADUs allowed
CA state lawYes — by right
ADUs and JADUs are allowed by right in all residential and mixed-use zones; ministerial approval, no hearing.
Units on a single-family lot
CA state law1 ADU + 1 JADU
At least one ADU and one JADU per single-family lot (a conversion ADU may also be possible).
Units on a multifamily lot
Local ruleconversions (>=1 or 25% of units) + up to 2 detached
Local cap of 2 detached ADUs on multifamily lots, less than state default of 8.
Junior ADU (JADU)
CA state lawAllowed
Up to 500 sq ft, within the walls of an existing single-family home (single-family lots only).
Size & height
Max detached ADU size
Local rule1,000 sq ft
Detached ADUs: 850 sq ft (1 bedroom or less), 1,000 sq ft (2+ bedrooms); up to 1,200 sq ft only with affordability covenant/exception.
Max attached ADU size
Local rule50% of primary, up to 850 (1BR) or 1,000 (2+BR), >=800
Attached ADUs capped at 850/1,000 sq ft, but must allow at least 800 sq ft if 50% rule yields less.
Guaranteed minimum size
CA state law800 sq ft
An 800 sq ft ADU must be allowed regardless of FAR/lot-coverage caps; a city also cannot cap an attached ADU below 850 sq ft (1,000 for 2+ bedrooms).
Max JADU size
CA state law500 sq ft
Max height
Local rule18 ft
Detached ADUs: 18 ft, plus 2 ft for matching roof pitch (max 20 ft); attached ADUs: up to 25 ft or zone limit.
Setbacks
Side setback
CA state law4 ft
A city cannot require more than 4 ft side or rear setback; conversions of existing structures are exempt.
Rear setback
CA state law4 ft
Front setback
CA state lawNo front setback may block the mandatory 800 sq ft / 16-ft / 4-ft-setback ADU; otherwise per base zone
Separation from main house
CA state lawNone required
No statewide separation requirement between the ADU and the primary dwelling.
Parking
Parking required
Local ruleNone
No parking required for any ADU/JADU; all properties within ½ mile of transit.
Transit parking exemption
CA state lawYes — no parking required near transit & for conversions
No parking may be required within ½ mi walking distance of transit, in a historic district, for an ADU within an existing structure, within one block of car-share, or in certain permit-parking areas.
Garage-conversion replacement parking
CA state lawNot required
When a garage/carport is demolished or converted to build an ADU, replacement parking cannot be required.
Approval, timeline & cost
Approval path
CA state lawMinisterial (by right)
No public hearing or discretionary design review for a qualifying ADU.
Approval timeline
CA state law60 days
The agency must act within 60 days of a complete application — and the ADU is deemed approved if it does not.
Owner-occupancy
Local ruleOnly for a JADU
Owner-occupancy required for JADUs only; not for ADUs.
Impact-fee waiver
CA state lawWaived under 750 sq ft
An ADU of 750 sq ft or less pays no impact fees (the 750 sq ft threshold itself is exempt under § 66311.5); larger ADUs pay fees proportional to the primary dwelling. JADUs (≤ 500 sq ft) are exempt.
Permits required
CA state lawBuilding permit
Only a ministerial building permit — no conditional use permit or discretionary design review for a qualifying ADU.
Piedmont-specific factors that can change the answer
State law sets the floor, but these local conditions often decide whether a specific parcel works.
Very High Fire Hazard Severity Zone (VHFHSZ)
Sprinklers required in ADU only if required for primary dwelling.
Piedmont limits detached ADUs to 1,000 sq ft (or 850 sq ft for 1-bedroom), and allows only 2 detached ADUs on multifamily lots. No parking is required for ADUs or JADUs anywhere in the city.
Frequently asked questions
Can I build an ADU in Piedmont?
Yes. California's statewide ADU law requires Piedmont to approve a qualifying accessory dwelling unit ministerial (by right), plus a junior ADU (JADU) on a single-family lot.
How big can an ADU be in Piedmont?
A detached ADU of at least 1,000 sq ft must be allowed, and an ADU of 800 sq ft can never be zoned out by floor-area or lot-coverage limits. A JADU can be up to 500 sq ft.
What are the setback requirements for an ADU in Piedmont?
Side and rear setbacks are limited to 4 ft. No front setback may block the mandatory 800 sq ft / 16-ft / 4-ft-setback ADU; otherwise per base zone.
Is parking required for an ADU in Piedmont?
None. No parking can be required within ½ mile of transit, for conversions, or for units inside the primary home. When a garage is converted, replacement parking is not required.
How long does ADU approval take in Piedmont?
A complete application must be acted on within 60 days, with ministerial (by right) — no public hearing or discretionary design review for a qualifying ADU.
Do I have to live on the property to build an ADU in Piedmont?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- Piedmont City Code, Division 17.38; Ord. 772 N.S. (March 2024)
- Piedmont City Code § 17.38.060(D)(1)-(4)
- Piedmont City Code § 17.38.060(B)(1); § 17.38.070
- Piedmont City Code § 17.38.060(B)(1)
- Piedmont City Code § 17.38.060(B)(4)
- Piedmont City Code § 17.30.020, Table 17.30.020
- Piedmont City Code § 17.38.060(C)(3)(b)-(c)
- Piedmont City Code § 17.38.060(B)(6)(d)
- Cal. Gov. Code §§ 66310–66342 (ADU Law)
- HCD 2025 Accessory Dwelling Unit Handbook
- Cal. Gov. Code § 66317 (ministerial approval, 60-day deadline)
- Cal. Gov. Code § 66323 (by-right ADU/JADU, 800 sq ft, 4-ft setbacks)
- Cal. Gov. Code § 66333 (junior ADUs)
- Cal. Gov. Code § 66321 (size minimums & height)
- Cal. Gov. Code § 66322 (ADU parking; § 66334 covers JADU parking)
- Cal. Gov. Code § 66314 (local ordinance standards)
- Cal. Gov. Code § 66311.5 (impact fees: none for an ADU ≤ 750 sq ft or JADU ≤ 500 sq ft)
Last updated March 2024. This is an AI-assisted summary of Piedmont's ADU rules, drawn from its published ordinance and California ADU law — general information, not legal advice, and it may be incomplete or out of date. Verify the controlling rule for your specific parcel with Piedmont Planning before relying on it.
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