General Contractor · Marin County · ADU Specialists
Solid Bay Construction SF designs, permits, and builds accessory dwelling units across Marin County — from Mill Valley to San Rafael. Our in-house architects, structural engineers, and permit expeditors handle every step, so you get a rental-ready ADU without juggling multiple contractors.
Why Marin Homeowners Build ADUs
Marin County ADU laws allow most single-family homeowners to build one ADU and one Junior ADU by right, without a discretionary hearing. A garage conversion ADU typically costs $180,000–$350,000 and can add $200,000–$500,000+ in property value — plus rental income potential of $2,500–$4,500/month depending on the city.
What We Build
Convert an existing garage into a full living unit. Fastest and most cost-effective ADU path in Marin.
A standalone unit built in your backyard, ideal for larger Marin lots in Mill Valley, Ross, and Kentfield.
Common in San Rafael and Corte Madera homes with daylight basements.
A smaller unit within your existing home's footprint, the fastest and least expensive option.
Investment
Service Area
Mill Valley · Tiburon · San Rafael · Sausalito · Corte Madera · Larkspur · Kentfield · Ross · San Anselmo · Fairfax · Novato
Why Solid Bay for Your Marin ADU
2 architects, 2 structural engineers, 2 designers, and a dedicated permit expeditor. No subcontracting your design.
We know each Marin city's building department process — San Rafael, Mill Valley, and Marin County unincorporated areas all have different requirements. Our expeditor manages all of them.
Many Marin ADU sites involve hillside grading, septic systems, or well water. Our structural engineers handle the added complexity flat-lot SF contractors don't see.
Fixed-price contracts, milestone-based payments, zero hidden fees.
Marin County ADU FAQ
Yes. Under current California law, most single-family properties in Marin County can build one ADU and one Junior ADU by right. Some hillside or septic-dependent lots require additional engineering review, which our team handles in-house.
Garage conversions typically run $180,000–$350,000. Detached new-construction ADUs run $350,000–$600,000+ depending on size and site conditions.
Design and permitting typically take 4–8 months; construction takes 4–8 months depending on ADU type. Total timeline is usually 9–16 months start to finish.
Yes — our in-house structural engineers coordinate with septic and well specialists for Marin properties outside sewer service areas, which is common in parts of Mill Valley and unincorporated Marin.
Ready to Start?
Tell us about your property. We'll respond within one business day with a preliminary scope assessment.