ADU Construction Cost in Fontana, CA (2026)
A adu construction in Fontana costs $250–$415 per sq ft, with a typical mid-size ADU running $75k–$150k. Small projects start around $50k; large or high-end work can reach $374k or more.
Costs in Fontana run about 17% below the LA County baseline thanks to Inland Empire labor rates and newer suburban housing.
ADU Construction Cost by Size in Fontana
Totals adjusted for the Fontana market (0.83× LA County baseline). Ranges include labor, materials, permits, and contractor overhead.
| Size | Type | Range | Low | High |
|---|---|---|---|---|
| Small | JADU / studio | 150–400 sq ft | $50k | $108k |
| Medium | 1-bed garage conversion | 400–600 sq ft | $75k | $150k |
| Large | Detached 2-bed | 800–1,200 sq ft | $208k | $374k |
What Affects ADU Construction Cost in Fontana?
- ADU type (JADU vs attached vs detached).
- Site prep and grading.
- Utility connections.
- CA Title 24 energy compliance.
- City ADU permit timeline.
- Fontana market premium: local pricing reflects Inland Empire labor rates and newer suburban housing, which shifts totals about 17% below the LA County baseline.
Get exact adu construction bids in Fontana
We'll match you with up to 3 licensed Fontana contractors.
Get MatchedADU Construction Sub-Type Comparisons
Garage Conversion ADU vs Detached ADU
Garage conversions reuse the existing slab and shell at $90k–$180k; a detached new-build ADU runs $250k–$450k but unlocks larger floor plans and higher rent.
Junior ADU (JADU) vs Attached ADU
A JADU (≤500 sq ft, within the home) runs $60k–$130k and shares utilities; an attached ADU is a true second unit at $150k–$350k with its own entrance and meter.
How to Get the Best Price on a ADU Construction in Fontana
- Get 3 line-itemized bids on the same scope through Keystone Connect — Fontana adu construction pricing varies 10–25% between contractors.
- Lock major materials and finishes before signing; mid-project change orders are the #1 cost driver on adu construction jobs.
- Bid in shoulder seasons (Jan–Mar or Sep–Oct) when Fontana contractor schedules are open and rush premiums disappear.
- Verify CSLB license, insurance, and bond before paying any deposit. California caps deposits at $1,000 or 10% of contract, whichever is less.
Frequently Asked Questions — ADU Construction in Fontana
Need more answers? Visit our contractor FAQ hub.
Get Matched with Licensed Fontana Contractors
Tell us about your adu construction and we'll match you with up to 3 vetted contractors.