Ontario, San Bernardino County

Room Addition Cost in Ontario, CA

Ontario remodeling costs are 15% belowthe California state average. Here's what a typical room addition costs in Ontario in 2026, based on a 300 sqf project.

Budget
$51,000
$170/sqf
Mid-Range
$89,250
$298/sqf
High-End
$140,250
$468/sqf

Cost breakdown

Foundation & Framing
30%$26,775
Roofing & Exterior
15%$13,388
Mechanical (HVAC, Electrical)
15%$13,388
Interior Finishes
20%$17,850
Windows & Doors
10%$8,925
Permits & Engineering
10%$8,925

Breakdown based on mid-range estimate of $89,250

Typical Timeline
3-6 months
Permits Required

Building permit, structural engineering, possibly zoning approval.

Remodeling in Ontario

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

A room addition adds square footage and value to your home. Costs depend on whether it's a simple bump-out, a second story, or a full wing addition with plumbing.

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Other projects in Ontario

Kitchen Remodel
$25,500 – $76,500
Bathroom Remodel
$12,750 – $40,800
ADU / Guest House
$106,250 – $255,000
Roof Replacement
$10,625 – $31,875
Exterior Paint
$4,250 – $14,875
Whole House Remodel
$229,500 – $765,000

Room Addition cost in other California cities

Riverside
$51,000 – $140,250 | Riverside County
Culver City
$66,000 – $181,500 | Los Angeles County
Long Beach
$60,000 – $165,000 | Los Angeles County
San Diego
$60,000 – $165,000 | San Diego County
Arcadia
$66,000 – $181,500 | Los Angeles County
Chula Vista
$57,000 – $156,750 | San Diego County
El Monte
$54,000 – $148,500 | Los Angeles County
Los Angeles
$63,000 – $173,250 | Los Angeles County

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