Foster City, San Mateo County

ADU / Guest House Cost in Foster City, CA

Foster City remodeling costs are 25% abovethe California state average. Here's what a typical adu / guest house costs in Foster City in 2026, based on a 500 sqf project.

Budget
$156,250
$313/sqf
Mid-Range
$250,000
$500/sqf
High-End
$375,000
$750/sqf

Cost breakdown

Foundation & Framing
25%$62,500
Mechanical (HVAC, Plumbing, Electrical)
20%$50,000
Interior Finishes
20%$50,000
Exterior & Roofing
15%$37,500
Kitchen & Bath Fixtures
10%$25,000
Permits, Plans & Engineering
10%$25,000

Breakdown based on mid-range estimate of $250,000

Typical Timeline
4-8 months
Permits Required

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

Remodeling in Foster City

Planned community built on reclaimed land in the 1960s-70s. Homes are reaching the age where major systems need replacement. Lagoon-adjacent properties have specific moisture considerations.

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 Foster City

Kitchen Remodel
$37,500 – $112,500
Bathroom Remodel
$18,750 – $60,000
Room Addition
$75,000 – $206,250
Roof Replacement
$15,625 – $46,875
Exterior Paint
$6,250 – $21,875
Whole House Remodel
$337,500 – $1,125,000

ADU / Guest House cost in other California cities

Castro Valley
$137,500 – $330,000 | Alameda County
Fremont
$143,750 – $345,000 | Alameda County
Benicia
$125,000 – $300,000 | Solano County
San Bruno
$150,000 – $360,000 | San Mateo County
Lafayette
$150,000 – $360,000 | Contra Costa County
Livermore
$131,250 – $315,000 | Alameda County
San Ramon
$143,750 – $345,000 | Contra Costa County
Belmont
$156,250 – $375,000 | San Mateo County

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