Home Additions & ADU in Sausalito - One Fixed Price, Permits Handled

Fast, Reliable Home Additions & ADU Across Sausalito

If you’re reading this, you’ve probably already discovered the hard truth about adding square footage in Sausalito: most contractors won’t even return your call once they see the hillside, the floating home, or the stair access on your street. We will. A home addition or ADU in Sausalito typically lands between $45,000 and $130,000 for land-based work, with detached ADUs running $90,000 to $220,000 and garage conversions falling between $30,000 and $80,000. Barrett & Sons Construction has been owner-operated since 1998, and Tom Barrett’s crews know the 94965 and 94966 hillsides well enough to quote honestly the first time. Call (877) 610-1318 and we’ll schedule a free estimate without the runaround.

Call (877) 610-1318

Why Barrett & Sons Construction Is Sausalito’s Preferred Home Additions & ADU Company

Tom Barrett started this company in 1998 with one rule: his name goes on the truck, so his name goes on the work. Our Home Additions & ADU team carries that same rule on every Sausalito job, from the floating homes off Gate 5 Road to the mid-century hillside houses above Bridgeway. Tom’s sons run the crews most days, which means you’ll see the same faces from the first site visit to the final inspection walkthrough.

We answer our own phone. Not a call center, not a voicemail box that takes three days. Call (877) 610-1318 and a live person picks up, 24 hours a day. For Home Additions & ADU in Sausalito, that matters when the marine layer rolls in and you need to know whether your foundation plan handles the serpentine soil correctly, or whether your ADU sightlines will clear the neighbor’s deck. We’ve worked enough hillside lots above Spring Street to know the answer usually lives in the permit drawings, which we pull ourselves.

Every price change on a Sausalito project arrives as a written change order before work proceeds. No allowance surprises. No end-of-job invoice that makes your jaw drop. And every completed job carries our 90-Day Done Right Promise in writing: one call brings Tom back to make it right. We also publish our name, address, and license number openly. Look us up before you sign anything.

Our Home Additions & ADU Services in Sausalito

ADU Design & Permitting

Sausalito’s building department sees a steady stream of ADU applications, and the hillside setbacks, view corridor rules, and geotechnical reports for serpentine soil mean the design and permitting phase can stretch for months if you don’t know the territory. We handle the full package: drafting, structural engineering, permit submittal, and corrections. We’ve helped homeowners in the hills off Caledonia Street get accessory units approved without fighting the planner on their own. Every permit gets pulled, every inspection gets signed, and you get a copy of both.

Garage Conversion ADU

A garage conversion in Sausalito usually runs $30,000 to $80,000, which is often the most practical path to a legal rental unit on lots where a detached ADU won’t fit. Many older Sausalito garages have post-and-pier foundations that shift on the clay-heavy slopes, so we typically include foundation inspection and reinforcement in the scope from the start. We also handle the utility upgrades, the seismic anchoring, and the insulation details that make a converted garage feel like a real apartment, not a finished box.

New Detached ADU

For a new detached ADU in Sausalito, plan on $90,000 to $220,000 depending on size, site access, and finish level. If your lot sits on a steep hillside above Spencer Avenue or near the 94965 corridor, the excavation and footing work becomes the largest variable. We work with local geotechnical engineers who know the serpentine soil behavior at the mouth of the Golden Gate, and we stage material deliveries to minimize disruption to neighbors who share a narrow road. You’ll get a written scope with every allowance itemized before we break ground.

Junior ADU & Interior Conversion

The least expensive way to add separate living space in Sausalito is a junior ADU or interior conversion, often carved from an oversized bedroom, a lower-level bonus room, or an underused family space. These projects typically stay under the $45,000 to $130,000 range and frequently come in lower than a full addition when the existing footprint works. We’ve converted hillside bedrooms above Bridgeway into compact studio units with their own entrance and kitchenette, and we handle the plumbing, electrical, and egress requirements the county expects. If you’re also considering Kitchen Remodeling in Sausalito alongside an interior ADU, we can bundle the scopes to share the permit and demolition phases.

Trusted Brands We Service in Sausalito

We don’t install mystery materials off the back of a van. On Sausalito ADU and addition work, you’ll see names like Techo-Bloc for retaining wall block and paving at the unit entry, Cambridge Pavers where a new hardscape connects to the main house, and Quikrete products for structural concrete and repair work on hillside footings. We specify brands we’d put on our own homes, and we keep them consistent across the estimate, the change orders, and the installed work. If you want to look up the manufacturer and verify the spec, we’ll hand you the product sheet. If you’re also planning Bathroom Remodeling in Sausalito inside the addition, the same rule applies: named brands, written scope, no surprises.

Common Home Additions & ADU Problems We See in Sausalito Homes

• Salt air eating unprotected metal. Sausalito sits right at the mouth of the Golden Gate, and the constant marine fog carries enough salt to corrode standard steel flashings, anchor bolts, and railing hardware years ahead of schedule. We spec hot-dipped galvanized or stainless fasteners on exposed connections and marine-rated lumber where moisture contact is unavoidable.
• Serpentine soil shifting foundations. The hillside neighborhoods above Bridgeway sit on some of the most unstable soil in Marin County. Older post-and-pier foundations built in the 1960s and 1970s shift enough to crack walls and bind doors, and any addition needs a geotechnical report before the structural engineer will even sign off. We coordinate that report ourselves so the project doesn’t stall.
• Stair access that breaks out-of-area contractors. Above Spring Street, many homes have no driveway and no alley. Every stud, every sack of concrete, every beam gets hand-carried up 60 to 100 steps or flown in by crane. Bidders who haven’t seen Sausalito’s hillsides before routinely underprice the labor, then disappear or demand change orders halfway through. We price it honestly from the first walkthrough.
• Floating home regulations no land contractor knows. The floating-home community off Gate 5 Road along Richardson Bay operates under dock and hull permitting rules that simply don’t exist for land-based construction. Below-waterline materials, tidal movement tolerances, and marine-grade fasteners are not optional upgrades; they’re baseline code. We’ve completed enough floating-home ADU and deck work to know what the harbor master and the county will both require.

Pricing for Home Additions & ADU in Sausalito, CA

We Also Serve Cities Near Sausalito

While this page focuses on Home Additions & ADU in Sausalito, our crews work throughout the immediate area. We handle additions and ADUs in Tiburon, Tamalpais Valley, Tamalpais-Homestead Valley, and Mill Valley as well. Same owner-operated crews, same written scope rule, same 90-Day Done Right Promise.

FAQs - Home Additions & ADU in Sausalito