Ontario, San Bernardino County

ADU / Guest House Cost in Ontario, CA

Ontario remodeling costs are 15% belowthe California state average. Here's what a typical adu / guest house costs in Ontario in 2026, based on a 500 sqf project.

Budget
$106,250
$213/sqf
Mid-Range
$170,000
$340/sqf
High-End
$255,000
$510/sqf

Cost breakdown

Foundation & Framing
25%$42,500
Mechanical (HVAC, Plumbing, Electrical)
20%$34,000
Interior Finishes
20%$34,000
Exterior & Roofing
15%$25,500
Kitchen & Bath Fixtures
10%$17,000
Permits, Plans & Engineering
10%$17,000

Breakdown based on mid-range estimate of $170,000

Typical Timeline
4-8 months
Permits Required

Building, electrical, plumbing, mechanical. May require plan check.

Remodeling in Ontario

Growing Inland Empire city with new construction and renovation activity. Proximity to logistics hubs means material delivery is efficient.

California allows ADUs on most residential lots since 2020. An ADU adds living space and rental income. Cities must approve or deny within 60 days of a complete application.

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Other projects in Ontario

Kitchen Remodel
$25,500 – $76,500
Bathroom Remodel
$12,750 – $40,800
Room Addition
$51,000 – $140,250
Roof Replacement
$10,625 – $31,875
Exterior Paint
$4,250 – $14,875
Whole House Remodel
$229,500 – $765,000

ADU / Guest House cost in other California cities

Los Angeles
$131,250 – $315,000 | Los Angeles County
Santa Rosa
$137,500 – $330,000 | Sonoma County
San Francisco
$168,750 – $405,000 | San Francisco County
Morgan Hill
$137,500 – $330,000 | Santa Clara County
Mill Valley
$162,500 – $390,000 | Marin County
San Jose
$156,250 – $375,000 | Santa Clara County
Menlo Park
$168,750 – $405,000 | San Mateo County
San Anselmo
$150,000 – $360,000 | Marin County

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