Folsom adopted a completely rewritten ADU ordinance (Ord. 1361, FMC Chapter 17.105) effective May 14, 2026, folding design review into the building permit and codifying the state's 60-day deemed-approval rule. State-protected '66323 units' — including any detached ADU up to 800 sq ft — skip local design standards entirely, while larger units face objective design rules (and strict architectural styles in the Historic District). Notably, Folsom's code allows ADUs to be sold separately to qualified buyers under Gov. Code 66341.
Zoning & Size Requirements [1][2]
Yes — Folsom allows ADUs. A detached ADU can typically be up to 1,000 sq ft under current California and Folsom zoning rules.
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| Allowed Zones | All parcels zoned for single-unit, two-unit, or multi-unit residential use with an existing or proposed primary dwelling; JADUs on single-unit parcels |
| Max Size (Detached) | 850 sq ft (1 bedroom or fewer) or 1,000 sq ft (2+ bedrooms); an 800 sq ft ADU with 4-ft setbacks can never be precluded; minimum 150 sq ft |
| Max Size (Attached) | 850 sq ft (1BR) or 1,000 sq ft (2+BR), and no more than 50% of the primary dwelling's floor area |
| Max Size (JADU) | 500 sq ft |
| Max Height | Detached: 25 ft or the height of the primary residence, whichever is less (state Gov. Code 66321 heights — 16-18 ft — apply to 66323 units and near listed historic structures). Attached: underlying zone height; 25 ft max where encroaching into the primary dwelling's setback area |
| Max Units | Single-unit lot: 1 attached/detached ADU + 1 conversion ADU + 1 JADU + 1 new detached 66323 ADU (per FMC 17.105.120); multifamily: conversions up to 25% of units plus 2 detached (proposed MF) or up to 8 detached (existing MF); SB 9 lots capped at 2 total units |
Setback Requirements [1][2]
Folsom requires a rear setback of about 4 ft for a detached ADU, and one off-street parking space is required. Owner-occupancy is not required — you can rent it out without living on the property.
| Rear Setback | 4 ft; none for conversions of existing structures |
| Side Setback | 4 ft; none for conversions; detached ADUs must be 6 ft from the primary dwelling and other structures |
| Front Setback | Front setback of the underlying zone; ADU may not break the front plane of the primary dwelling; rear-yard coverage capped at 40% |
| Parking Required | 1 space per ADU or per bedroom, whichever is less (driveway/tandem OK); waived within 1/2 mile walking distance of public transit, in the Historic District, for conversions, and other state exemptions; no replacement parking for garage conversions |
| Owner Occupancy | Not required for ADUs. JADUs: required only if the JADU shares sanitation facilities with the main home (AB 1154 codified in FMC 17.105.160) |
| Min Lot Size | No minimum lot size |
Permit Process & Fees [3]
An ADU permit in Folsom typically costs Standard building permit and plan check fees; a planning application fee applies only if design review is required — confirm amounts with Folsom Community Development and takes Completeness check within 15 business days; approval or denial within 60 days of a complete application — deemed approved if the city misses the deadline (codified per SB 543), through a ministerial, by-right review.
| Approval Process | Ministerial building permit; design review now runs concurrently within the building permit for non-66323 units; 66323 units (including ≤800 sq ft detached) are exempt from design standards |
| Review Timeline | Completeness check within 15 business days; approval or denial within 60 days of a complete application — deemed approved if the city misses the deadline (codified per SB 543) |
| Permit Fees | Standard building permit and plan check fees; a planning application fee applies only if design review is required — confirm amounts with Folsom Community Development |
| Impact Fees | No city impact fees for ADUs of 750 sq ft or less (or JADUs ≤500 sq ft); proportional to primary dwelling size above 750 sq ft |
| Plan Check | Combined design review + building permit saves an estimated 3-4 weeks versus the old two-step process |
| Pre-Approved Plans | No city-published pre-approved plan library found — confirm options with Folsom Community Development |
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Construction Costs [4][5]
Building an ADU in Folsom typically costs $150,000-$300,000 ($250-$400 per sq ft); a garage conversion runs $80,000-$150,000.
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| Average Build Cost | $150,000-$300,000 |
| Cost per Sq Ft | $250-$400 |
| Garage Conversion | $80,000-$150,000 |
| Prefab ADU (Installed) | $120,000-$250,000 |
Finance Your ADU Project
Most ADU projects are funded through HELOCs, construction loans, or cash-out refinancing. Compare rates from top lenders.
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Rental Income Potential [6][7]
A 2-bedroom ADU in Folsom rents for around $2,300-$2,600/mo, an estimated 6-9% annual return.
| Avg Rent (1 Bedroom) | $1,900-$2,150/mo |
| Avg Rent (2 Bedroom) | $2,300-$2,600/mo |
| Short-Term Rental | No — rentals must be 30 days or longer (FMC 17.105.070); ADUs cannot be vacation rentals |
| Est. Annual ROI | 6-9% annual return |
Explore Prefab ADU Options
Prefab ADUs can save 20-40% vs. traditional construction and cut build time in half.
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Recent Law Changes
What's Changed Recently
- Ord. 1361: fully rewritten ADU chapter (FMC 17.105) took effect May 14, 2026, aligning with Gov. Code 66310-66342
- Design review merged into the building permit for ADUs, cutting an estimated 3-4 weeks from review times
- Separate sale of ADUs to qualified buyers now expressly allowed per Gov. Code 66341 (FMC 17.105.070)
- AB 1154 codified: JADU owner-occupancy applies only where the JADU shares a bathroom with the primary dwelling
Tips for Building an ADU in Folsom
- Keep a detached ADU at 800 sq ft or less with 4-ft setbacks to qualify as a '66323 unit' and skip Folsom's design standards entirely
- In the Historic District, larger ADUs must match one of the city's prescribed architectural styles (Craftsman, Queen Anne, Delta, etc.) — the 800 sq ft exemption avoids this
- Detached ADUs outside the 66323 path can reach 25 ft — rare two-story flexibility for the Sacramento region
- Folsom expressly allows condo-style separate sale of ADUs to qualified buyers, a potential exit-value advantage
ADU Builders in Folsom
Looking for an ADU builder in Folsom? ADU projects need a contractor experienced with local zoning, the permit process, and utility connections — not every general contractor has built one. We match Folsom homeowners with experienced local ADU contractors who provide free, no-obligation quotes. Getting at least three bids typically saves 20-40% on the same scope.
Sources & References
All data on this page is sourced from official government records and verified market data. View our full methodology.
- FMC Chapter 17.105 Accessory Dwelling Units (Ord. 1361, 2026) Municipal Code — Accessed 2026-07-10
- Accessory Dwelling Units | City of Folsom Planning Department — Accessed 2026-07-10
- City Updates and Streamlines Requirements for ADUs | City of Folsom News Planning Department — Accessed 2026-07-10
- Folsom, CA ADU Information | GatherADU industry — Accessed 2026-07-10
- Folsom, California | ADU Rules, Plans, and Guides | Dwellito industry — Accessed 2026-07-10
- Average Rent in Folsom, CA | Zumper Market Data — Accessed 2026-07-10
- Average Rent in Folsom, CA | RentCafe Market Data — Accessed 2026-07-10
Frequently Asked Questions
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