ADU Builders in Folsom, CA (2026)

An ADU builder in Folsom is a licensed contractor who designs and constructs accessory dwelling units — detached backyard units, garage conversions, attached additions, and junior ADUs (JADUs). Because an ADU is a complete second dwelling, the builder coordinates foundation, framing, plumbing, electrical, and HVAC work and pulls it through Folsom's permit process and utility connections. Not every general contractor has built one, so the right builder is one with ADU-specific experience in California.

What ADU Builders Cost in Folsom ^[11]^[12]^[13]^[14]

Based on our Folsom cost data, expect the following ranges from local ADU builders. Quotes for the same scope typically vary 20-40% between contractors, so getting at least three bids is the single best way to control cost.

New Detached ADU (all-in)	$170,000-$400,000
Cost per Sq Ft	$250-$500
Garage Conversion	$90,000-$200,000
Prefab / Modular ADU (installed)	$170,000-$340,000
City Permit & Plan Review	Flat building permit fee of $4,852 per detached or attached ADU and $2,329 per JADU, covering plan review and inspections (Res. 11481, effective July 1, 2026), plus an $81 processing fee and state surcharges; design review for a non-66323 unit adds $400 (Director level).
Impact Fees	No city impact fees for an ADU of 750 sq ft or less or a JADU of 500 sq ft or less (FMC 17.105.060(C)); above 750 sq ft each city fee is prorated by ADU floor area divided by primary-dwelling floor area. Water and sewer connection or capacity charges are not charged unless the ADU is built with a new house (17.105.060(B)). The July 1, 2026 North of 50 schedule totals about $26,200 in city impact fees for a new single-family home (roads $9,903, park equipment $8,532, general $1,936, fire $1,316, drainage $1,257, water $1,194, light rail $878, police $728, smaller items), so a 1,000 sq ft ADU behind a 2,000 sq ft house would owe roughly half; the Folsom Plan Area south of Hwy 50 has its own higher schedule. School district fees are collected separately.

For a full line-item breakdown, see our Folsom ADU cost guide. To confirm what you're allowed to build before you hire, review the Folsom ADU rules (max detached size: 1,000 sq ft with 2 or more bedrooms, 850 sq ft with 1 bedroom or fewer, measured as interior living space, minimum 150 sq ft (FMC 17.105.150(B)(2)). A new detached unit of 800 sq ft or less with 4-ft setbacks is a '66323 unit' exempt from design review, and no standard may preclude an 800 sq ft ADU (17.105.150(C)(2)). Detached ADUs on two-unit and multi-unit lots are capped at 800 sq ft (17.105.170(B)(2)).; owner-occupancy: Not required for ADUs. JADUs: required only when the JADU shares a bathroom with the main house (FMC 17.105.160(B)(4), matching Gov. Code 66333 as amended by AB 1154, effective Jan 1, 2026); a JADU with its own bathroom has no owner-occupancy rule.).

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How to Vet an ADU Builder in Folsom

License: Confirm a current contractor's license in California and that it's in good standing. Ask for the license number and verify it with the state board.
ADU-specific experience: Ask how many ADUs they've completed in or near Folsom and request addresses or photos. ADU permitting and setbacks differ from a kitchen remodel.
Portfolio & references: Get references from recent ADU clients and, if possible, visit a finished unit.
Insurance: Verify general liability and workers' compensation coverage. Ask for a certificate of insurance.
Written, detailed bid: Insist on an itemized, fixed-price or clearly-scoped bid — not a verbal estimate. It should state whether permits (Flat building permit fee of $4,852 per detached or attached ADU and $2,329 per JADU, covering plan review and inspections (Res. 11481, effective July 1, 2026), plus an $81 processing fee and state surcharges; design review for a non-66323 unit adds $400 (Director level).), plan check (Plan check is bundled into the flat ADU permit fee and covers up to three review cycles; a fourth cycle, revisions and deferred submittals bill at $194 per hour and expedited review costs 1.5x (Res. 11481, Building Fees Sec. D). Side or rear setbacks under 5 ft trigger extra Fire Code construction requirements; retaining walls over 4 ft or grading over 50 cubic yards need separate permits; work on a protected tree needs a Tree Permit.), and impact fees (No city impact fees for an ADU of 750 sq ft or less or a JADU of 500 sq ft or less (FMC 17.105.060(C)); above 750 sq ft each city fee is prorated by ADU floor area divided by primary-dwelling floor area. Water and sewer connection or capacity charges are not charged unless the ADU is built with a new house (17.105.060(B)). The July 1, 2026 North of 50 schedule totals about $26,200 in city impact fees for a new single-family home (roads $9,903, park equipment $8,532, general $1,936, fire $1,316, drainage $1,257, water $1,194, light rail $878, police $728, smaller items), so a 1,000 sq ft ADU behind a 2,000 sq ft house would owe roughly half; the Folsom Plan Area south of Hwy 50 has its own higher schedule. School district fees are collected separately.) are included.
Permit handling: Confirm they manage Folsom's permit process ("Ministerial building permit filed in the Folsom ePermit Center under permit type 'ADU – Accessory Dwelling Unit' with the Residential Projects Checklist (Form B210) and the optional zoning checklist for your ADU type (Forms CD-P213/214/215). Units that are not 66323 units get a concurrent ministerial design review by the Community Development Director inside the building permit (FMC 17.105.110, 17.06.045); no Planning or Historic District Commission hearing. Planning assigns the ADU's address after issuance.", typically Completeness notice within 15 business days; decision within 60 days of a complete application, deemed approved if the city misses it (FMC 17.105.050; Gov. Code 66317). The city says merged design review saves an estimated 3-4 weeks and a pre-reviewed Master Plan about 30 days more.) and who is responsible if revisions are required.
Payment schedule: Avoid large upfront payments. A reasonable schedule ties payments to completed milestones.

Questions to Ask Before You Hire

How many ADUs have you built in Folsom in the last two years?
Is your bid fixed-price, and what would trigger a change order?
Are permits, plan check, and utility connection fees included?
What's a realistic timeline, including permit review (Completeness notice within 15 business days; decision within 60 days of a complete application, deemed approved if the city misses it (FMC 17.105.050; Gov. Code 66317). The city says merged design review saves an estimated 3-4 weeks and a pre-reviewed Master Plan about 30 days more.) and construction?
Who is my point of contact and how are delays communicated?
What warranty do you provide on workmanship?
Can you share three recent California ADU client references?

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Frequently Asked Questions

How much do ADU builders charge in Folsom?

ADU builders in Folsom typically quote $170,000-$400,000 for a new detached unit, or about $250-$500 per square foot, including design, permitting, and construction. A garage conversion runs $90,000-$200,000 and a prefab/modular ADU averages $170,000-$340,000. Add city permit and plan-review fees (Flat building permit fee of $4,852 per detached or attached ADU and $2,329 per JADU, covering plan review and inspections (Res. 11481, effective July 1, 2026), plus an $81 processing fee and state surcharges; design review for a non-66323 unit adds $400 (Director level).) plus impact fees of No city impact fees for an ADU of 750 sq ft or less or a JADU of 500 sq ft or less (FMC 17.105.060(C)); above 750 sq ft each city fee is prorated by ADU floor area divided by primary-dwelling floor area. Water and sewer connection or capacity charges are not charged unless the ADU is built with a new house (17.105.060(B)). The July 1, 2026 North of 50 schedule totals about $26,200 in city impact fees for a new single-family home (roads $9,903, park equipment $8,532, general $1,936, fire $1,316, drainage $1,257, water $1,194, light rail $878, police $728, smaller items), so a 1,000 sq ft ADU behind a 2,000 sq ft house would owe roughly half; the Folsom Plan Area south of Hwy 50 has its own higher schedule. School district fees are collected separately.. Quotes for the same scope commonly vary 20-40% between builders, so collect at least three bids.

How do I find a good ADU builder in Folsom?

Look for a licensed contractor with completed ADU projects in Folsom specifically — ADUs involve local zoning, setback rules, and utility connections that general remodelers may not have handled. Verify the license, ask for an ADU-specific portfolio and references, confirm they carry liability and workers' comp insurance, and get a written fixed-price or detailed bid. Submit a request below and we'll forward it to local ADU builders serving Folsom for free quotes.

Do ADU builders in Folsom handle permits?

Most full-service ADU builders manage the permit process for you. In Folsom the approval process is "Ministerial building permit filed in the Folsom ePermit Center under permit type 'ADU – Accessory Dwelling Unit' with the Residential Projects Checklist (Form B210) and the optional zoning checklist for your ADU type (Forms CD-P213/214/215). Units that are not 66323 units get a concurrent ministerial design review by the Community Development Director inside the building permit (FMC 17.105.110, 17.06.045); no Planning or Historic District Commission hearing. Planning assigns the ADU's address after issuance." with a typical review timeline of Completeness notice within 15 business days; decision within 60 days of a complete application, deemed approved if the city misses it (FMC 17.105.050; Gov. Code 66317). The city says merged design review saves an estimated 3-4 weeks and a pre-reviewed Master Plan about 30 days more.. Confirm in writing whether permit fees, plan check (Plan check is bundled into the flat ADU permit fee and covers up to three review cycles; a fourth cycle, revisions and deferred submittals bill at $194 per hour and expedited review costs 1.5x (Res. 11481, Building Fees Sec. D). Side or rear setbacks under 5 ft trigger extra Fire Code construction requirements; retaining walls over 4 ft or grading over 50 cubic yards need separate permits; work on a protected tree needs a Tree Permit.), and impact fees are included in the bid or billed separately.

How long does it take to build an ADU in Folsom?

Plan for the permit review (Completeness notice within 15 business days; decision within 60 days of a complete application, deemed approved if the city misses it (FMC 17.105.050; Gov. Code 66317). The city says merged design review saves an estimated 3-4 weeks and a pre-reviewed Master Plan about 30 days more. in Folsom) plus construction. Most detached ADUs take 4-8 months of construction after permits are issued; garage conversions and prefab units are often faster. Ask each builder for a realistic schedule and what could delay it.

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Build Cost	$170,000-$400,000
Garage Conv.	$90,000-$200,000
Permit Fees	Flat building permit fee of $4,852 per detached or attached ADU and $2,329 per JADU, covering plan review and inspections (Res. 11481, effective July 1, 2026), plus an $81 processing fee and state surcharges; design review for a non-66323 unit adds $400 (Director level).
Timeline	Completeness notice within 15 business days; decision within 60 days of a complete application, deemed approved if the city misses it (FMC 17.105.050; Gov. Code 66317). The city says merged design review saves an estimated 3-4 weeks and a pre-reviewed Master Plan about 30 days more.
1BR Rent	$1,650-$2,400/mo

What ADU Builders Cost in Folsom [11][12][13][14]