San Mateo, San Mateo County

Room Addition Cost in San Mateo, CA

San Mateo remodeling costs are 25% abovethe California state average. Here's what a typical room addition costs in San Mateo in 2026, based on a 300 sqf project.

Budget
$75,000
$250/sqf
Mid-Range
$131,250
$438/sqf
High-End
$206,250
$688/sqf

Cost breakdown

Foundation & Framing
30%$39,375
Roofing & Exterior
15%$19,688
Mechanical (HVAC, Electrical)
15%$19,688
Interior Finishes
20%$26,250
Windows & Doors
10%$13,125
Permits & Engineering
10%$13,125

Breakdown based on mid-range estimate of $131,250

Typical Timeline
3-6 months
Permits Required

Building permit, structural engineering, possibly zoning approval.

Remodeling in San Mateo

Central Peninsula location with strong remodeling demand. Mix of pre-war bungalows and mid-century ranches. The city's permitting department is moderately efficient by Bay Area standards.

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 San Mateo

Kitchen Remodel
$37,500 – $112,500
Bathroom Remodel
$18,750 – $60,000
ADU / Guest House
$156,250 – $375,000
Roof Replacement
$15,625 – $46,875
Exterior Paint
$6,250 – $21,875
Whole House Remodel
$337,500 – $1,125,000

Room Addition cost in other California cities

Long Beach
$60,000 – $165,000 | Los Angeles County
San Carlos
$75,000 – $206,250 | San Mateo County
Pleasant Hill
$63,000 – $173,250 | Contra Costa County
Redwood City
$75,000 – $206,250 | San Mateo County
San Bruno
$72,000 – $198,000 | San Mateo County
Dublin
$66,000 – $181,500 | Alameda County
Novato
$69,000 – $189,750 | Marin County
Oakland
$72,000 – $198,000 | Alameda County

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