Folsom ADU Regulations: A Comprehensive Guide 2026

Folsom is one of the fastest-growing cities in the Sacramento region, with an estimated 92,000+ residents as of 2026 and steady new housing demand. 

On mostly built-out lots, Accessory Dwelling Units (ADUs) have become a key way to add housing, create rental income, and support multigenerational living without leaving your neighborhood.

What Is an ADU (and a JADU) in Folsom?

The City of Folsom defines an Accessory Dwelling Unit (ADU) as a second, smaller dwelling on a lot that already has (or will have) a home or apartment building. It must: 

• Provide independent living (sleeping, eating, cooking, bathroom).
• Be on a permanent foundation.
• Have its own exterior entrance.
• Include at least an efficiency kitchen (sink with drain, cooking appliance, counter, cabinets).

Folsom also recognizes Junior ADUs (JADUs): 

• Located entirely inside the existing or proposed primary home.
• Max 500 sq. ft.
• Can share a bathroom with the main house.
• Must have an efficiency kitchen and separate exterior entrance.

The city explicitly bans using ADUs as vacation rentals (no renting for less than 30 days). 

Why ADUs Make Sense in Folsom

• Fast population growth: Folsom’s population has jumped past 92,000 residents with ~4% annual growth, leading the state in housing and population expansion. 
• Strong jobs + transit: Major employers (Intel, state agencies, hospitals) and light-rail access to downtown Sacramento make small rentals attractive. 
• Multigenerational living: ADUs let you keep parents, college-age kids, or caregivers close while still giving everyone privacy.
• Property value: State housing analysis shows ADUs reliably add value and increase total housing supply. 

Can I Build an ADU in Folsom?

Under Folsom Municipal Code Chapter 17.105, ADUs are allowed on parcels that: 

• Are zoned for single-unit, two-unit, or multi-unit residential use, and
• Have an existing or proposed dwelling on the lot.

Key allowances:

• Single-family lots:
  • Up to 1 ADU (attached or detached), plus 1 JADU on the same lot. 
• Two-unit / multifamily lots:
  • At least 1 ADU is allowed, with additional options to convert interior space to multiple ADUs under state law. 

The ordinance also states no minimum parcel size or width is required to build an ADU, so even smaller city lots can qualify. 

Folsom ADU Laws & Regulations (2026)

Below are the most important local rules, plus state-law protections that apply in Folsom.

Unit Types Allowed in Folsom

Folsom’s ADU program allows several formats: 

• Detached ADU – a separate backyard cottage.
• Attached ADU – physically connected addition to the main house.
• Conversion ADU – converting an existing garage or accessory structure.
• Interior conversion – carving out existing space inside the home.
• Junior ADU (JADU) – ≤500 sq. ft. inside the existing home or attached garage, with an efficiency kitchen and separate entrance.

Maximum Unit Size

Folsom’s ordinance and state law work together here:

“By-right” minimum that must be approved

State law and Folsom’s ADU ordinance guarantee that the city cannot deny: 

• Any ADU up to 800 sq. ft.,
• 16 ft or less in height,
• With 4-ft side and rear setbacks,

as long as basic building-code and safety standards are met (this applies even in the Historic District).

Detached ADUs – single-family lots

Under Chapter 17.105.070: 

• Must meet the “efficiency unit” standard.
• Maximum size:
  • Up to 850 sq. ft. for 0–1 bedroom.
  • Up to 1,000 sq. ft. for 2+ bedrooms.

So the practical range for detached ADUs in Folsom is roughly 400–1,000 sq. ft., with 800 sq. ft. as the easiest “sure-thing” threshold.

Attached ADUs

For attached ADUs, Folsom’s code and state law require at least: 

• 850 sq. ft. allowed for studio/1-bed units.
• 1,000 sq. ft. allowed for 2+ bedrooms.

Attached ADUs also have to fit within lot-coverage rules and usually cannot be larger than the primary dwelling’s living area.

Junior ADUs

• Max 500 sq. ft., entirely within the existing or proposed primary dwelling. 

ADU Height Limits

Folsom sets clear height caps, especially important near the Historic District: 

• Detached ADUs (new construction):
  • Default max height: 16 ft.
• Attached ADUs:
  • Can exceed 16 ft, but:
    • In the Historic District, they may not exceed 25 ft or the height of the main house, whichever is lower.
    • Outside the Historic District, they may not exceed 30 ft or the height of the main house, whichever is lower.
• Conversions over existing garages/accessory structures:
  • Can keep the existing height; additional design standards may apply.

Remember: an 800 sq. ft. ADU at or below 16 ft gets the most straightforward approval under both city and state rules. 

Setback Requirements

For single-family lots, the main rules are: 

• Side & rear yard (detached ADUs):
  • Minimum 4 ft from the property line.
• Front yard:
  • Detached ADUs generally must stay behind the front plane of the primary dwelling and meet the same front setback requirements as the main house.
• Corner lots:
  • ADUs can’t extend beyond a 4-ft interior and street-side setback, and cannot project in front of the primary dwelling’s front plane.
• Separation from other buildings:
  • Detached ADUs must be at least 6 ft from the main house or other accessory structures, not counting fences/walls.

Folsom also limits rear-yard coverage for ADUs to no more than 40% of the rear yard or 800 sq. ft., whichever is greater, and ADUs cannot encroach on required open-space areas. 

Parking Requirements

Local rules + state law combine like this: 

• Baseline city rule:
  • One off-street parking space is required for each attached or detached ADU.
  • This is in addition to the spaces required for the main house.
  • Spaces may be tandem and on a paved driveway, but cannot block sidewalks or sit in unpaved front yards.
• State-law exemptions (apply in Folsom):

The city may not require any parking for an ADU if, for example:

• It is within ½ mile walk of public transit (e.g., light rail or certain bus stops).
• It is within the existing home or a conversion of an existing garage/accessory structure.
• It is an 800-sq-ft or smaller detached ADU that meets state “by-right” criteria.

Folsom even provides an ADU Parking Requirement Map showing where extra parking is and isn’t required. 

Building Permits and Fees

A building permit is always required for an ADU in Folsom. 

• If the ADU is ≤800 sq. ft. and ≤16 ft tall, many projects can go straight to Building for permits.
• If it’s larger than 800 sq. ft. or taller than 16 ft, you must submit to Planning first for zoning review (setbacks, height, design standards), then to Building. 

 

Applications go through the city’s ePermit Center online. 

Fees and impact fees

• Under state law, no development impact fees may be charged for ADUs smaller than 750 sq. ft. 
• For larger ADUs, impact fees must be proportional to the size of the ADU relative to the main house.
• You’ll still pay plan check and building permit fees, plus any utility connection fees required by service providers.

State law also requires Folsom to process ADU permits ministerially (no public hearings) and generally within 60 days of a complete application. 

Design Requirements

Folsom relies on objective design standards and a detailed ADU Design Workbook, especially for the Historic District. 

Key themes:

• Compatibility: ADUs should use similar materials, roof pitch, and colors as the main house and appear visually subordinate.
• Historic District:
  • ADUs here follow additional design standards and, if over 16 ft tall, may require Historic District Commission review—but the city cannot use design rules to block an 800-sq-ft, 16-ft-tall ADU with 4-ft side/rear setbacks. 
• Private entrance: Every ADU (and JADU) must have a direct exterior entrance. 

Utilities and Infrastructure

Folsom’s ordinance is relatively flexible on utilities: 

• The city cannot require a new or separate utility connection for attached or detached ADUs unless the utility provider itself requires it.
• Homeowners may choose to install a separate meter/connection for easier billing.
• Any utility fees must comply with California ADU law (reasonable and proportionate).

The city also provides a specific “ADUs and Electrical Service” guide to help you plan for panel upgrades and service capacity. 

You’ll still need standard water, sewer, and storm-drain solutions, but many ADUs simply tie into the existing home’s laterals if capacity allows.

Owner-Occupancy & Renting

ADUs (standard attached or detached)

• Folsom’s website stresses that ADUs may not be used as short-term vacation rentals (no stays under 30 days). 
• Thanks to AB 976 and updated state law, cities may not require owner-occupancy for ADUs at all—permanently. 
  • In practice, this means in Folsom you can rent out both the main house and the ADU on standard (30+ day) leases.

Junior ADUs (JADUs)

• State law still allows (and effectively expects) owner-occupancy for JADUs via a recorded deed restriction. 
• Folsom provides a Sample JADU Deed Restriction Form, indicating the property owner must live in either the JADU or the main house. 

Property Taxes

Building an ADU in Folsom increases your property taxes, but only on the new value created by the ADU:

• Under Proposition 13, the base property tax rate in California is 1% of assessed value. 
• Sacramento County confirms that the actual tax rate is 1% plus bonded debt for your tax-rate area. 
• When you add an ADU, the County Assessor issues a supplemental assessment for the new construction, and you may get a one-time supplemental bill on top of your regular bill. 

In practice, most owners in the Sacramento region end up paying roughly 1.1–1.3% of the ADU’s added value per year once local bonds and assessments are included. 

New ADU Laws in 2026 That Affect Folsom

Several statewide reforms shape how Folsom must handle ADUs:

1. No Owner-Occupancy for ADUs (AB 976 & 2026 ADU Handbook)
   • The 2026 ADU Handbook confirms that local agencies are permanently prohibited from imposing owner-occupancy requirements on ADUs. 
2. Pre-Approved ADU Plans (AB 1332)
   • Every city must have an ADU plan pre-approval program by January 1, 2026.
   • Jurisdictions must review pre-approval applications in 60 days, and site-specific permits using pre-approved plans in 30 days. 
   • Folsom may adopt its own pre-approved plan gallery or accept plans pre-approved by other agencies.
3. Unpermitted ADU Amnesty (AB 2533)
   • Local agencies can’t deny permits for unpermitted ADUs built before January 1, 2020 solely because they violate current codes, unless there’s a genuine health/safety issue. 
4. Parking & Street-Improvement Limits (SB 1211)
   • Reinforces that cities cannot pile on extra parking or street-widening requirements just because a homeowner is building an ADU. 
5. Updated Government Code Sections & Timelines
   • ADU and JADU rules are now in Gov. Code §§ 66310–66342; the 2026 Handbook clarifies standards and enforces the 60-day permit deadline statewide. 

All of this pushes cities like Folsom to keep their ADU processes fast, predictable, and builder-friendly.

Folsom ADU Laws: Key Takeaways

For a homeowner in Folsom in 2026, here’s the quick snapshot:

• You can almost certainly build an ADU on any residential lot with an existing or proposed home; there’s no minimum lot size. 
• On a typical single-family parcel, you’re allowed:
  • 1 ADU (attached or detached), plus
  • 1 JADU inside the main house. 
• A “safe” by-right option is an ADU up to 800 sq. ft., 16 ft tall, with 4-ft side/rear setbacks, which the city must approve ministerially, even in the Historic District. 
• Detached ADUs can go up to 850–1,000 sq. ft. depending on bedroom count, with one extra off-street parking space unless a state exemption applies (near transit, conversion, ≤800 sq. ft., etc.). 
• Owner-occupancy is not required for ADUs, but is required for JADUs, and ADUs can only be rented on 30-day-plus leases (no vacation rentals). 
• Your property tax bill will increase only on the new assessed value of the ADU, typically around 1.1–1.3% of that value per year in the Sacramento region.