ADU Construction in Foster City, CA

Quartz Construction builds accessory dwelling units (ADUs) in Foster City, CA. Whether you need a detached backyard ADU, a garage conversion, or a junior ADU, our licensed team handles everything — design, permits, and construction. Licensed CSLB #1003436 | BBB A+ | 4.9⭐ (65+ Reviews)

ADU Types We Build in Foster City

• Detached Backyard ADU — Separate, self-contained unit in your backyard. Ideal for rental income or family member housing.
• Attached ADU — Addition to your existing home with separate entrance and utilities.
• Garage Conversion ADU — Transform your Foster City garage into a fully permitted living space at lower cost.
• Junior ADU (JADU) — Smaller unit within your existing home structure, permitting often simpler.
• Above-Garage ADU — Second-story unit built over your existing garage.

ADU Cost in Foster City

ADU construction in Foster City costs $155,000–$360,000 for a detached ADU. Garage conversions are more affordable at $60,000–$120,000. The high cost of housing in Foster City means a well-built ADU typically rents for $2,500–$4,500/month, achieving full ROI in 5–8 years.

ADU Permits in Foster City

California state law (AB 2221, SB 9) allows ADUs on all single-family lots, including in Foster City. Foster City has streamlined its ADU permit process in compliance with state mandates. Quartz Construction handles all permitting, engineering, and inspections — you don’t need to navigate City Hall alone.

ADU Rental Income in Foster City

ADU rental income in Foster City typically ranges $2,200–$4,000/month depending on size and finishes. With Bay Area rents this high, most Foster City homeowners recoup their ADU investment within 6–8 years while simultaneously increasing their property value by $200,000–$400,000+.

Get a Free ADU Estimate in Foster City

Ready to build an ADU in Foster City? Quartz Construction provides free ADU consultations including site assessment, permit feasibility review, and construction estimate. Call (650) 749-7436 or fill out our contact form. CSLB #1003436 | BBB A+ | Serving Foster City and all Bay Area cities.