Folsom ADU Guide: Permits, Costs & 2026 Rules

Folsom Just Rewrote Its ADU Rules

Folsom hadn't touched its ADU ordinance since 2020. State ADU law moved fast in the years after that, and by the end of 2025 the city's local rules were noticeably behind. In December 2025, the California Department of Housing and Community Development sent Folsom a letter telling it to catch up. The council took a first reading on the rewrite March 24, 2026, a second reading April 14, and Ordinance No. 1361, repealing and re-enacting Folsom Municipal Code Chapter 17.105, took effect May 14, 2026.

The practical upshot: design review used to be a separate step from the building permit review. It isn't anymore — the two now run together, and the ordinance reorganized the rules by ADU type with new checklists so it's easier to tell upfront which standards actually apply. In a change that surprises a lot of homeowners, a single-family lot in Folsom can now support up to 3 ADUs plus 1 Junior ADU, and a multifamily property up to 8 detached ADUs. Most people still build one at a time, but the ceiling is a lot higher than it used to be.

If you're weighing whether this pencils out for your lot, run a free estimate at SafewayQuickQuote.com. It takes about two minutes and doesn't require a site visit.

The Folsom ADU Permit Process

California law makes ADU approval ministerial. If your plans meet the building and zoning code, Folsom has to approve them — no discretionary hearing, no neighbor vote, no planning commission vote required by state law.

One clarification worth stating plainly, because it trips people up: Folsom is its own incorporated city, not a permitting sub-office of Sacramento County. A lot of the surrounding region routes through city or county systems in Sacramento proper, so it's an easy assumption to make — but a Folsom ADU permit is reviewed entirely in-house here. If a contractor's proposal for a Folsom address references county processing, that's worth a follow-up question.

Folsom accepts ADU applications electronically through its ePermit Center; submittals go through a completeness check before entering the review queue, and incomplete packages get sent back with a list of what's missing. The city's own posted target is a 15-day completeness check followed by 10 to 20 days for the initial plan review, with California's 60-day ministerial approval cap as the outer limit for a complete, code-compliant application. In practice, design-through-permit-issuance commonly runs about 3 to 4 months.

Folsom also runs its own fire department and its own water and sewer utility, so you're generally not chasing sign-offs from a separate special district the way you might in some smaller cities nearby.

ADU Size, Setback & Height Rules in Folsom (2026)

Detached ADU

• Maximum size: Folsom Municipal Code Chapter 17.105 caps a detached ADU at 850 square feet if it has one bedroom or fewer, or 1,000 square feet for two or more bedrooms — smaller than the 1,200-square-foot ceiling some neighboring Sacramento-region cities allow
• State-protected “66323” units: any detached ADU of 800 square feet or less, 16 feet or lower, with 4-foot side/rear setbacks, cannot be denied and skips local design review entirely
• Setbacks: 4 feet minimum, side and rear
• Units between 801 and 1,000 square feet face Folsom's objective design standards — general compatibility with the main house in style, materials, and colors

Attached ADU

• Maximum size: up to 50% of the primary home's floor area, with a state-guaranteed floor of at least 800 square feet
• Setbacks generally follow the primary dwelling's

Junior ADU (JADU)

• Maximum size: 500 square feet, built within the existing or proposed home
• Owner occupancy required, in either the main home or the JADU

Multiple units

• Single-family lots: up to 3 ADUs plus 1 JADU
• Multifamily properties: up to 8 detached ADUs

Parking

Convert your garage into an ADU and Folsom cannot require replacement parking — that's settled by state law. New ADUs within a half mile of transit also skip the added-parking requirement. JADUs never require additional parking.

There's a genuine trade-off here: build small — 800 square feet or under, 16 feet or under — and you skip design review outright, the closest thing Folsom has to a fast lane. Push toward the city's 850-to-1,000-square-foot maximum and you pick up an objective design review step along with the bigger unit. Run the numbers on both before committing to a floor plan.

Folsom ADU Costs (2026)

Per square foot: $200 to $280/sq ft for garage conversions; roughly $265 to $390/sq ft for new detached construction, trending toward the upper half given Folsom's price point relative to some neighboring cities.

Typical permit fees and soft costs (grounded in the surrounding Sacramento-region cluster; treat as planning ranges and confirm exact figures with the city before finalizing a budget):

Here's a real difference from most of our other Sacramento-region guides: Folsom does not currently have a published pre-approved ADU plan catalog. Davis, the City of Sacramento, and Elk Grove all publish free, ready-to-build plans that skip most of that $6,000-to-$15,000 design fee. Folsom hasn't posted one as of this writing, so budget for full custom design regardless of which size you build. We cover which Sacramento-region cities do and don't have a live catalog in our pre-approved ADU plans comparison — worth a read before assuming Folsom works like its neighbors.

The 750-square-foot line still matters for impact fees: under it, state law exempts you entirely; at or above it, fees scale proportionally to your ADU's size relative to your home's. Get a written fee quote from Building Services before finalizing a budget.

Want a number specific to your lot and unit size? Run the free Safeway ADU cost calculator or get a two-minute estimate at SafewayQuickQuote.com.

Utilities: SMUD Electric, PG&E Gas, and Folsom's Own Water System

Folsom runs on a two-utility split that catches some homeowners off guard: SMUD provides electricity across the entire city, including Folsom Ranch, the large new development south of Highway 50, where new electric infrastructure is going in as the area builds out. PG&E remains the natural gas provider for the same addresses — SMUD is an electric-only municipal utility and has never sold gas anywhere. Because the city's own materials sometimes list “SMUD and PG&E” together without spelling out who does what, confirm directly with whichever one holds your account before scheduling ADU electrical work.

For an ADU with a full kitchen and HVAC load, an older 100-amp panel commonly needs to go to 200 amps — budget $3,000 to $6,500 through SMUD if your service is maxed out. A gas range, tankless water heater, or gas furnace runs through PG&E separately.

Water, sewer, and trash in Folsom are handled directly by the City of Folsom, not by SMUD, PG&E, or an outside special district — simpler than several neighboring cities where homeowners also coordinate with a standalone sewer or fire district. If your home predates the 1980s, ask Building Services to confirm your sewer lateral condition — older clay laterals are a common, unglamorous line item on an ADU budget.

Timeline: From Design to Move-In

Building at 800 square feet or under with a 16-foot roofline skips local design review entirely and moves straight through the state-mandated ministerial review. Push into the 850-to-1,000-square-foot range and you add a design review step to the same combined process — still faster than the old pre-2026 two-track system, but not instant. We manage the submittal, the completeness corrections, and the design review documentation so none of that lands back on your calendar.

What Different Parts of Folsom Should Budget For

Historic Folsom / Sutter Street. The city maintains a dedicated ADU design workbook for the Historic District, and larger units here generally face more design scrutiny — confirm current requirements with the Historic District Commission before finalizing plans. That makes the smaller, state-protected 800-square-foot category worth a close look. Older downtown homes, some Victorian-era with mid-century ranches mixed in, tend to carry older electrical service and clay sewer laterals, so budget realistically for the utility connection line item.

Empire Ranch and Broadstone. These 2000s-era subdivisions near the Palladio shopping district generally have modern electrical service already in place, which keeps panel-upgrade costs off the table more often than in older Folsom. Lots here run smaller, which pushes many homeowners toward an attached ADU or garage conversion instead of a full detached unit. If your property sits under an HOA, check its architectural guidelines separately from the city's process.

Folsom Ranch. This is still an active growth area south of Highway 50, with new electric and gas infrastructure going in as phases open. Larger lots here make it easier to actually reach Folsom's full 1,000-square-foot detached maximum, something tighter in-town lots can struggle to fit once setbacks are accounted for. Leave some schedule flexibility for utility hookups as construction volume keeps pace with infrastructure.

Outside city limits. Folsom borders El Dorado Hills across the county line. If your parcel sits in El Dorado County rather than the City of Folsom, none of the information above applies — confirm which jurisdiction your address falls in before you start.

Rental Income: What a Folsom ADU Can Earn

Folsom rents run above most of the Sacramento region. One-bedroom apartments have averaged roughly $2,050 to $2,200 a month in 2026, two-bedrooms roughly $2,450 to $2,600. A private, well-finished backyard ADU with its own entrance typically competes at or above those comps.

Intel remains Folsom's largest single employer, even after rounds of layoffs over the past year, and Micron has a presence in the city too — that keeps a base of tech-sector renters looking for housing close to work. A permitted, well-built ADU in Folsom typically adds $150,000 to $275,000 to appraised value, a bit above the regional average given the city's price point.

Frequently Asked Questions

Related Guides

• Elk Grove ADU Guide: Permits, Costs & Pre-Approved Plans (2026)
• Sacramento ADU Guide: Permits, Costs & Rental Income (2026)
• Pre-Approved ADU Plans in the Sacramento Region: A 2026 City-by-City Comparison
• Sacramento Garage Conversion ADU: Costs & Rules (2026)
• Safeway ADU Cost Calculator