Best ADU Builders in Fontana, CA
Compare vetted, CSLB license-verified ADU builders and ADU contractors in Fontana. The average cost to build an ADU in Fontana is $250–$400 per square foot. Top-rated builders include Acton ADU, WM Construction, Villa Homes.
Every builder below is CSLB license-verified, bonded, and insured — vetted before they ever reach a homeowner. Browse ratings and real reviews, compare starting prices, or let us match you with the best fit for your lot and budget. It's free; we're paid by the builders, not you.
Find your builder · Step 1 of 4
What kind of ADU are you planning?
ADU activity in Fontana
ADU projects in Fontana commonly budget $250-$400 per sq ft, or about $200,000-$320,000 for an 800 sq ft ADU, before site conditions, utility upgrades, and finish choices.
Showing 4 of 4 builders in Fontana, CA
Last updated July 16, 2026
License VerifiedActon ADU
Serving Fontana, CA · Campbell, CA
“We had a great experience working with Acton ADU on our ADU project, and I want to give a special shoutout to Sandro. Sandro was fantastic from start to finish—…”— N K
Pricing on request
A California general building contractor licensed since 1992, serving the LA market statewide.
License VerifiedWM Construction
Serving Fontana, CA · Fontana, CA
“⭐️⭐️⭐️⭐️⭐️ Outstanding Emergency Plumbing Service! I had an unexpected plumbing emergency at my house, and these guys came through big time. From the moment I…”— Marian Sedra
Pricing on request
CSLB-verified B contractor in Fontana, CA.
Get matched with a vetted ADU builder in Fontana, CA — for free
- Hand-matched to license-verified builders for your lot
- Compare real quotes — no obligation, no spam
- 100% free; we're paid by the builders, not you
License VerifiedVilla Homes
Serving Fontana, CA · San Francisco, CA
“Excellent job! The Villa crew from start to finish nothing short of professional. Foundation, home delivery, finish work etc top notch. I would recommend Vill…”— M Ferreira
Pricing on request
Tech-enabled prefab ADU builder delivering turnkey backyard homes across California.
License VerifiedNestadu
Serving Fontana, CA · Mill Valley, CA
“Nestadu did a great job on my backyard ADU. Their team was professional, and the final result looks fantastic—well-built and blends in nicely with my home. Pric…”— Stephen Reid
Pricing on request
Custom and prefab ADUs for California homeowners — design, permit, and build, turnkey.
Need a vetted ADU builder in Fontana?
Share your lot, budget, and timeline once. We'll match you with license-verified builders who fit the project.
Frequently Asked Questions
- How much does it cost to build an ADU in Fontana, CA?
- In Fontana, ADUs typically run $250–$400 per square foot all-in. A detached 800 sq ft unit commonly lands between $230k and $340k depending on finishes, site conditions, and utility connections. Garage conversions are the most affordable path, often under $180k.
- How long does it take to build an ADU in Fontana?
- Plan to budget 6–12 months end to end. California law caps ADU plan check at 60 days for compliant designs, and construction usually takes 4–8 months after permits are issued.
- Do I need a permit to build an ADU in Fontana?
- Yes. All ADUs require a building permit, but California mandates ministerial (non-discretionary) approval for compliant units, so there's no public hearing or design review. Your builder typically pulls the permit on your behalf.
- How do I choose a builder in Fontana?
- Confirm the contractor holds an active CSLB license, is bonded and insured, and has built ADUs in Fontana specifically. Every builder in this directory is license-verified. Use "Get a Quote" to be matched with the best fit for your lot and budget.
ADU costs in Fontana: city vs. metro vs. state
Building an ADU in Fontana runs roughly $250–$400 per square foot all-in. Here's how the city benchmarks against the broader metro and statewide averages.
| Area | Avg. cost / sq ft | Typical 800 sq ft ADU |
|---|---|---|
| Fontana | $250–$400 | $200,000–$320,000 |
| Fontana metro | ~$320 | ~$256,000 |
| California (CA) | ~$330 | ~$264,000 |
Cost by ADU type in Fontana
| ADU type | Typical size | Project cost | Timeline |
|---|---|---|---|
| Detached ADU | 600–1,200 sq ft | $180,000–$420,000 | 8–12 months |
| Attached ADU | 400–800 sq ft | $140,000–$300,000 | 6–10 months |
| Garage Conversion | 400–600 sq ft | $90,000–$180,000 | 4–7 months |
| JADU (Junior ADU) | ≤ 500 sq ft | $60,000–$140,000 | 3–6 months |
ADU rules & permits in Fontana, CA
Local ADU permitting in Fontana follows California state ADU law, which caps plan-check at 60 days for compliant units. Confirm setbacks, height, and parking rules with the local building department.
| Jurisdiction | Permit timeline | Permit fees | Notes |
|---|---|---|---|
| Fontana (independent city) | 60 days max by CA statute | Set by local ordinance | Permits are issued by the Fontana building department, not the City of Los Angeles |
| Statewide (CA) | 60 days max by statute | Varies | Ministerial approval; owner-occupancy requirement waived through 2030 |
Financing your ADU in Fontana
Common ADU funding paths include renovation and construction loans, a HELOC, or a cash-out refinance. ADU-specific lenders underwrite against after-build value, which often unlocks more than a standard HELOC.
Construction / renovation loan
Funds released in draws as the build hits milestones; underwritten against after-build value.
HELOC / home equity
Borrow against existing equity. Fast to set up if you have 20%+ equity.
Cash-out refinance
Replace your mortgage and pull equity as cash — best when rates are favorable.
ADU-specific lenders
RenoFi and similar lenders underwrite the projected value the ADU adds, often unlocking more.
Pre-ADU Checkup — $499 — Get finalized permits, a pre-ADU checklist, and an on-site feasibility visit. Homeowners save $1,000s by doing this before engaging a contractor.