Your Backyard Could Be Earning $4,500/Month

Build a fully permitted ADU and add $150,000+ to your home value. One team handles design, permits, construction, and move-in. Free site visit — no obligation.

“ConstruBay handled our entire ADU from permit submission to move-in day. They identified a setback issue on our lot before we ever signed — and redesigned around it without drama. The unit rented for $3,800 the first week it was listed.”

— Greg & Susan A.

Mill Valley · Detached ADU

AI-Powered Permit Planning

ConstruBay uses PlanPass.ai — an AI-powered construction permit intelligence platform — to accelerate Marin County permit approvals, flag issues before submission, and give clients real-time visibility into their permit status. No other contractor in Marin County offers this.

PlanPass.ai is a ConstruBay exclusive. It's how we protect your timeline and your investment.

How much does an ADU cost in Marin County?

ADU construction in Marin County ranges from $185,000 for a garage conversion to $650,000+ for a custom detached unit. Costs depend on size, finish level, hillside complexity, and permit requirements. ConstruBay provides fixed-scope contracts — what we quote is what you pay.

How long does ADU construction take in Marin County?

A typical ADU project takes 10–16 months from design to final inspection. Permit approval alone can take 4–8 months in Marin County depending on the jurisdiction. We use PlanPass.ai to accelerate the permit process and flag issues before submission.

Do I need a permit to build an ADU in Marin County?

Yes. All ADUs in Marin County require building permits. Some jurisdictions also require Design Review Board approval. ConstruBay handles the entire permit process — from application to final sign-off — using our AI-powered permit planning platform PlanPass.ai.

Can I build an ADU on a hillside lot in Marin County?

Yes, but hillside ADUs require geotechnical investigation, engineered retaining walls, and often a soils report. ConstruBay specializes in hillside construction across Mill Valley, Tiburon, and unincorporated Marin.

What ADU types does ConstruBay build?

We build detached ADUs, attached ADUs, garage conversions, and Junior ADUs (JADUs). Each type has different cost, size, and permitting requirements — we help you choose the right option for your lot and goals.