Building an ADU in Folsom

What you can build here

Folsom's ADU rules are in Folsom Municipal Code Chapter 17.105, repealed and re-enacted by Ordinance No. 1361, adopted April 14, 2026. The city says the changes "took effect on May 14, 2026." City slides say the state housing department (HCD) asked Folsom on December 5, 2025 to update its ordinance to match state law, and that HCD will review the adopted ordinance.

ADUs are allowed on lots zoned for single-unit, two-unit or multi-unit homes that have an existing or proposed home. Every ADU and junior ADU needs a building permit. The city says ADUs must have an outside entrance and a permanent foundation.

On a single-family lot the code lists, per lot:

• one attached or detached ADU that meets the city's standards,
• one ADU inside existing or proposed space in the house, or inside an existing accessory building,
• one junior ADU (JADU), and
• one new detached ADU of up to 800 sq ft under the state's streamlined rules.

The city's slides sum this up as "Up to 3 ADUs (attached, detached, and converted) and 1 JADU." Which combination fits your lot depends on its size and layout; confirm with the Planning Division.

Two ways to qualify. ADUs that fit state law's streamlined categories (conversions, JADUs, and new detached ADUs up to 800 sq ft with 4 ft side and rear setbacks) are "66323 Units": the city "shall approve" them, and they are exempt from the city's design standards and design review. All other ADUs must meet the city's objective design standards through a ministerial design review by the Community Development Director.

Apartment and duplex lots: you can convert non-living space into at least one ADU and up to 25% of the original units, and build up to two detached ADUs (proposed buildings) or up to eight (existing buildings, no more than the number of units). Those detached ADUs can be up to 800 sq ft.

On a lot created by an SB 9 lot split, the code allows no more than two units in total, counting ADUs and JADUs. See our California page and SB 9 lot split guide. [1][2][3]

Size, height and setbacks

Size is measured as interior living space, with a 150 sq ft minimum (an efficiency unit).

New detached ADU up to 800 sq ft (state-streamlined): 4 ft side and rear setbacks, height as allowed by state law, no city design standards.

Other detached ADUs:

• up to 850 sq ft with one bedroom or less, or 1,000 sq ft with two or more bedrooms;
• at least 4 ft from side and rear lines, and at least 6 ft from the house or another accessory building;
• can't sit in front of the front plane of the house;
• can't cover more than 40% of the rear yard, and must meet the zone's lot coverage;
• height "shall not exceed twenty-five (25) feet or the height of the residence, whichever is less."

Attached ADUs: up to 850 sq ft (one bedroom or less) or 1,000 sq ft (two or more), and no more than 50% of the existing house. The zone's front setback applies; side and rear setbacks are at least 4 ft. Height follows the zone, but any part inside the house's required setback is limited to 25 ft. The ADU's entrance must be on a different side of the building from the main entrance.

Converted space can keep the existing building's setbacks and height. The code says its standards can't block an ADU of at least 800 sq ft with 4 ft side and rear setbacks. The city recommends 5 ft side and rear setbacks "to avoid extra Fire Code requirements," and ADUs of 800 sq ft or less are exempt from lot coverage limits.

Check the height rule. State law says a city can't set a detached ADU height limit below 16 ft (more near transit). Folsom's "height of the residence" cap could be lower than that next to a short one-story house. Ask the Planning Division at 916-461-6202 how it applies.

Design standards (ADUs that aren't 66323 Units): attached ADUs use the house's wall materials; detached ADUs use at least two wall materials; roof pitch within 2/12 of the house's; second-story windows within 10 ft of a side or rear line must be translucent, transom, clerestory or false windows; one second-story balcony of up to 20 sq ft. You can ask for a waiver through design review. The Historic District has added standards.

Separate permits may be needed for removing protected trees, retaining walls over 4 ft, or grading of 50 cubic yards or more. [2][4][5]

Parking

The code requires "one (1) additional off-street parking space ... per accessory dwelling unit or per bedroom, whichever is less." It can be on a driveway in the front or side setback, or tandem on a driveway.

No parking is required when:

• the ADU is within a half-mile walk of public transit, including a bus stop or station,
• the ADU is in the historic district,
• the ADU is part of the house (attached ADU or JADU) or an existing accessory building,
• on-street parking permits are required but not offered to the ADU occupant,
• a car share vehicle is within one block, or
• the ADU is applied for together with a new home on the same lot and also meets one of the other exemptions.

If you remove or convert a garage, carport or parking space to build the ADU, you don't have to replace it.

State-streamlined ADUs. State guidance says cities "may not impose parking requirements on 66323 Units," which include a new detached ADU of up to 800 sq ft with 4 ft side and rear setbacks. Folsom's exemption list doesn't name that case, so confirm parking for one with the Planning Division at 916-461-6202. [2][5]

Fees

ADUs pay the standard building permit application and processing fees. ADUs that go through the planning (design review) process also pay an application fee set by the City Council; the city says design review "includes an additional plan review fee."

Impact fees. The code says "no City-imposed impact fees shall be charged" to an ADU of 750 sq ft or less, or a JADU of 500 sq ft or less. For a larger ADU, city impact fees are charged in proportion: the ADU's floor area divided by the house's floor area, times the fee for a new home. Fees from other agencies that the city collects follow those agencies' schedules. The city posts its impact fee schedules (North of 50 and Folsom Plan Area, effective July 1, 2026) on its fees page.

Utilities. An ADU isn't treated as a new residential use for water and sewer connection fees unless it is built with a new house, and the city can't make you install a separate utility connection unless the utility provider requires it.

School fees. You report the new square footage to Folsom Cordova Unified School District on form CD-B103, and the district decides what is due before the permit is issued. State guidance says ADUs under 500 sq ft are not subject to school impact fees.

See our ADU cost and ADU financing guides. [1][2][5][6][7]

How long it takes

Under the code, the city must tell you within 15 business days whether your application is complete. If it doesn't, the application is deemed complete. It must then approve or deny a complete ADU or JADU application within 60 days, or the application is deemed approved. The exceptions: the ADU is applied for together with a new main home (the city decides the ADU when it decides the home), or you ask for a delay.

If the city denies your application, it must give you written comments explaining how to fix it. You can appeal to the Planning Commission, which must decide within 60 business days.

The city says using an approved ADU Master Plan cuts "an estimated 30 days" from the typical time between submittal and permit issuance. See our ADU permit process guide. [2][4]

ADU Master Plan Program

Under its ADU Master Plan Program, Folsom lets designers and architects submit detached ADU plans for pre-review. Approved plans become "ADU Master Plans" listed on the city's website, and you can buy one from the designer for a streamlined permit review.

As of October 2026 the city's plan gallery says "ADU Master Plans are coming soon!" When plans are listed, you'll submit the plan exactly as approved, with a site plan for your lot; any change disqualifies the streamlined review, and the city says approval is "not guaranteed." [4][8]

Garage conversions and junior ADUs

Converting a garage, another accessory building or part of the house into an ADU is a state-streamlined "66323 Unit": the city must approve it, design standards don't apply, the space can keep its existing setbacks and height, and you can add up to 150 sq ft for getting in and out. No replacement parking is needed. See our garage conversion guide.

A junior ADU must be entirely within the existing or proposed space of the house, 150 to 500 sq ft, with an efficiency kitchen and its own outside entrance on a different side from the main entrance. If it shares the house's bathroom, it also needs an inside door to the house. No design standards apply, and no parking is needed. Before the permit is issued, you record a deed restriction (the city has a template, Form CD-P515) that bars selling the JADU separately.

Owner occupancy. The owner must live in the house or the JADU only if the JADU shares bathroom facilities with the house, matching state law. See our junior ADU guide. [1][2][5]

Renting out your ADU

An ADU or JADU may be rented separately from the house, but "the rental shall be for a term of thirty (30) days or longer." The city says ADUs "cannot be used as vacation rentals." No one may live in the ADU until the city approves occupancy of the main home.

The code's only provision for selling an ADU separately from the house is Gov. Code 66341, a narrow state exception for an ADU built by a qualified nonprofit and sold to a qualified buyer.

Older unpermitted ADUs. Until at least January 1, 2030, an owner of an ADU built before January 1, 2020 who gets a notice to correct violations can ask for up to five years' delay in enforcing a building standard, if the city finds it isn't a health and safety issue. An ADU may also raise your property taxes; see our ADU property tax guide. [1][2][5]

Permit steps in Folsom

1. Review the rules

   Read the city's ADU page, ADU Design Workbook and the checklist for your ADU type (attached, detached or junior). Ask zoning questions at 916-461-6202 or PlanningEPC@folsom.ca.us. [1]

2. Prepare plans

   Have plans and documents prepared per the Residential Projects Checklist (Form B210), with a site plan showing setbacks, utilities, pad elevation, drainage and lot coverage. Including the completed ADU checklist is optional but may speed review. [1][4]

3. Apply online

   In the city's ePermit Center, click Apply for a Permit and choose "ADU – Accessory Dwelling Unit." Upload all plans and documents at the time of application. [1][7]

4. Completeness check and plan review

   The city checks completeness (by code, within 15 business days), you pay plan review fees, and reviewers return comments for you to answer with revised plans. Larger ADUs get design review in the same process. [1][2][7]

5. Clear outside agencies and pay fees

   Complete the school district form (CD-B103) with Folsom Cordova Unified, then pay issuance and impact fees through eTRAKiT or at City Hall. [4][7]

6. Build, inspect and get an address

   Keep full-size approved plans on site for inspections. Certificate of Occupancy and final building inspections are required before anyone moves in. Ask the Planning Division to assign the ADU's address. [1][4][7]

Pre-approved and sample plans

• ADU Master Plan Program

  Designers' detached ADU plans pre-reviewed by the city for a streamlined permit; the gallery says plans are "coming soon." [4][8]

Who to call

• Planning Division

  ADU zoning, design review and address assignment; email PlanningEPC@folsom.ca.us

  916-461-6202

  50 Natoma Street, Folsom, CA 95630

  [1]

• Building Division

  Building permit applications, plan review and inspections; email EPC@folsom.ca.us

  916-461-6201

  50 Natoma Street, Folsom, CA 95630

  [1][7]

Questions people ask