Junior ADUs in Folsom

Short answer

Folsom allows one junior ADU alongside its listed ADU types on a single-family lot. State law limits a junior ADU to 500 sq ft within the residence, including an attached garage, and requires owner occupancy only when sanitation is shared with the house.

Last verified 2026-10-18. Rules change; the City of Folsom planning desk has the final word (916-461-6202).

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The rules

ADUs per single-family lotLocal rule: Up to 3 ADUs (one of each type) + 1 junior ADUFolsom Municipal Code 17.105.120(A)(1)
Planning deskLocal rule: PlanningEPC@folsom.ca.us, 916-461-6202City of Folsom Planning Division, ADU page
Junior ADU sizeState law: No more than 500 sq ft of interior livable space, contained within a single-family residenceGov. Code 66313(d)
Where a junior ADU can goState law: Within the single-family residence; an enclosed attached garage counts as part of itGov. Code 66333(d)
Junior ADU owner occupancy under state lawState law: Required when sanitation is shared with the house; not required when the junior ADU has separate sanitation facilitiesGov. Code 66333(b)
Junior ADU entranceState law: A separate entrance from the main home entrance; a shared-bathroom unit also needs interior entry to the main living areaGov. Code 66333(e)
Junior ADU kitchenState law: An efficiency kitchen with cooking appliances, a preparation counter and storage cabinetsGov. Code 66333(f)
Junior ADU deed restrictionState law: A recorded deed restriction bars selling the junior ADU separately from the homeGov. Code 66333(c)(1)
Junior ADU rental termState law: Longer than 30 daysGov. Code 66333(g)
State impact fee for a junior ADUState law: No impact fee at 500 sq ft of interior livable space or lessGov. Code 66311.5(c)(1)
Junior ADU rental term in the City codeLocal rule: 30 days or longerFolsom Municipal Code 17.105.070(A)

What to know in Folsom

A junior ADU can accompany Folsom's listed ADUs

Folsom Municipal Code 17.105.120(A)(1) lists one junior ADU alongside the allowed ADU types on a single-family lot. The state-law fact cards show the junior ADU's size and interior-location conditions.

Folsom Municipal Code 17.105.120(A)(1)

The City and state use different rental-term wording

Folsom's code says an ADU or junior ADU rental must last 30 days or longer. Government Code section 66333(g) says a junior ADU rental must last longer than 30 days. Confirm a term at that boundary with the Planning Division.

Folsom Municipal Code 17.105.070(A); Gov. Code 66333(g)

Estimated cost and rent

Garage conversions and junior ADUs aren't in this table for Folsom: the check can't verify them there yet, so a report lists them as not verified.

What we couldn't confirm

We could not confirm a Folsom-specific junior ADU permit and plan-check dollar total or whether a particular interior space passes building review.

Ask the City of Folsom planning desk before you rely on these.

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Our free check reads your lot against the Folsom rules above from public records: a screening, not a permit or professional advice.

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Floor plans to start from

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Folsom junior ADU questions

Can I add a junior ADU alongside an ADU in Folsom?

Yes, subject to the lot's other conditions. Folsom Municipal Code 17.105.120(A)(1) lists one junior ADU alongside its allowed ADU types on a single-family lot; Government Code section 66333(a) allows one junior ADU per qualifying lot.

Must I live at my Folsom home if it has a junior ADU?

Government Code section 66333(b) requires owner occupancy when the junior ADU shares sanitation with the house. It does not require owner occupancy when the junior ADU has separate sanitation facilities.

Can I rent a Folsom junior ADU for exactly 30 days?

Folsom Municipal Code 17.105.070(A) says 30 days or longer, while Government Code section 66333(g) says longer than 30 days for a junior ADU. Ask Folsom Planning before relying on a term of exactly 30 days.

Can a Folsom junior ADU use an attached garage?

Government Code sections 66313(d) and 66333(d) require a junior ADU to stay within the single-family residence and count an enclosed attached garage as part of it. Section 66333(e)-(f) also requires a separate entrance and an efficiency kitchen.

Is this a permit, or a plan I can build from?

Neither. It is a screening from public records, not professional advice, and not a survey, soils report, appraisal, loan offer or permit; every number is an estimate. A licensed designer confirms the final plan, and your city or county gives final approval.