California ADU rules · Sacramento County
Can I Build an ADU in Folsom?
Yes — you can build an ADU in Folsom. California's statewide ADU law requires every city, including Folsom, 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
CA state lawConversion ADUs (≥1, up to 25% of units) + up to 8 detached
Conversions of non-livable space (at least 1, or up to 25% of existing units) plus up to 8 detached ADUs on a lot with existing multifamily — never exceeding the number of existing units. JADUs are single-family only.
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
Folsom caps an ADU at 850 sq ft (≤1 bedroom) or 1,000 sq ft (2+ bedrooms). The 800 sq ft by-right floor still applies regardless of this cap. Confirm the size tier against FMC Ch. 17.105 for your bedroom count.
Max attached ADU size
CA state law50% of the primary dwelling, but ≥850 sq ft (≥1,000 sq ft for 2+ bedrooms) is always allowed
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 rule16 ft
Outside the Historic District a detached ADU may reach 30 ft (or the primary dwelling's height, whichever is less), but any ADU over 16 ft is subject to design review. State transit/two-story 18-ft allowances apply by right.
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
Local rulePer the primary structure's required front yard setback (a detached ADU's front setback may not be less than the primary dwelling's); side and rear setbacks are 4 ft
Separation from main house
Local rule6 ft
Folsom requires a detached ADU to be at least 6 ft from the main residence and other existing accessory structures. State law sets no separation requirement.
Parking
Parking required
CA state lawUp to 1 space
At most 1 space per ADU (or per bedroom, whichever is less) — and waived in the common cases below.
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
CA state lawOnly for a JADU
No owner-occupancy requirement for ADUs (the prior sunset was removed). A JADU may require owner-occupancy, principally where it shares sanitation with the main house.
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.
Folsom-specific factors that can change the answer
State law sets the floor, but these local conditions often decide whether a specific parcel works.
Folsom Historic District
An ADU over 16 ft in the Historic District requires design-review approval from the Historic District Commission (FMC Ch. 17.52); ADUs elsewhere over 16 ft are reviewed by the Community Development Director. ADUs must match the main home's style and materials, and second-story units need enclosed staircases.
Folsom updated its ADU chapter (Mun. Code Ch. 17.105) effective May 14, 2026 to align with state law while keeping its own standards: ADUs are capped at 850/1,000 sq ft by bedroom count, detached ADUs must sit at least 6 ft from the main house, the front setback follows the primary dwelling, and any ADU over 16 ft triggers design review — by the Historic District Commission inside the Historic District. Short-term (under-30-day) rental of an ADU is prohibited. Verify Historic District status and the applicable size/height tier with Folsom Community Development.
Frequently asked questions
Can I build an ADU in Folsom?
Yes. California's statewide ADU law requires Folsom 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 Folsom?
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 Folsom?
Side and rear setbacks are limited to 4 ft. Per the primary structure's required front yard setback (a detached ADU's front setback may not be less than the primary dwelling's); side and rear setbacks are 4 ft.
Is parking required for an ADU in Folsom?
Up to 1 space. 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 Folsom?
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 Folsom?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- Folsom Mun. Code Ch. 17.105 (Accessory Dwelling Units)
- 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 § 66315 (owner-occupancy)
- Cal. Gov. Code § 66311.5 (impact fees: none for an ADU ≤ 750 sq ft or JADU ≤ 500 sq ft)
Last updated 2026-06-28. This is an AI-assisted summary of Folsom'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 Folsom Planning before relying on it.
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