Fairfax, Marin County

Room Addition Cost in Fairfax, CA

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

Budget
$69,000
$230/sqf
Mid-Range
$120,750
$402/sqf
High-End
$189,750
$633/sqf

Cost breakdown

Foundation & Framing
30%$36,225
Roofing & Exterior
15%$18,113
Mechanical (HVAC, Electrical)
15%$18,113
Interior Finishes
20%$24,150
Windows & Doors
10%$12,075
Permits & Engineering
10%$12,075

Breakdown based on mid-range estimate of $120,750

Typical Timeline
3-6 months
Permits Required

Building permit, structural engineering, possibly zoning approval.

Remodeling in Fairfax

Bohemian Marin community with the most affordable housing in central Marin. Older, smaller homes with strong renovation potential. Hillside lots can complicate additions.

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 Fairfax

Kitchen Remodel
$34,500 – $103,500
Bathroom Remodel
$17,250 – $55,200
ADU / Guest House
$143,750 – $345,000
Roof Replacement
$14,375 – $43,125
Exterior Paint
$5,750 – $20,125
Whole House Remodel
$310,500 – $1,035,000

Room Addition cost in other California cities

Hayward
$63,000 – $173,250 | Alameda County
Cupertino
$78,000 – $214,500 | Santa Clara County
Sausalito
$78,000 – $214,500 | Marin County
Gilroy
$63,000 – $173,250 | Santa Clara County
Martinez
$60,000 – $165,000 | Contra Costa County
Morgan Hill
$66,000 – $181,500 | Santa Clara County
Moraga
$72,000 – $198,000 | Contra Costa County
Corte Madera
$72,000 – $198,000 | Marin County

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