A free site visit, a check of what your lot allows and a written, line-item price.
Get your free estimateFast, Reliable Home Addition Contractor Across Sausalito
A room addition in Sausalito typically runs $180,000 – $420,000 for a ground-level bump-out and $350,000 – $700,000 for a full second-story addition, with hillside foundation and coastal-spec materials pushing toward the upper end. Most Sausalito permits clear in 4 – 8 months, and construction takes 5 – 10 months depending on slope work, retaining walls, and the finish level you choose. Our Home Addition Contractor team knows the difference between a bid that survives contact with a Sausalito hillside and one that doesn’t. Call us at (707) 760-0502 for a written estimate that spells out every line item, including the marine-grade hardware that keeps your addition standing in salt air.
We’re the ADU company of the Kingswell family, and we’ve been building in Marin since 2010. This page tells you what actually fails in Sausalito’s coastal climate, what it costs to do it right, and how the Sausalito market prices additions compared to inland Marin. No fluff. Just the numbers and the material specs.
Why Lodgewick ADU San Francisco Is Sausalito’s Preferred Home Addition Contractor Company
Sausalito homeowners call us after other contractors’ work fails somewhere between year three and year seven. The pattern is nearly always the same: inland-spec fasteners, unsealed joints, and a foundation detail that ignored what marine air does to steel and concrete. We don’t make those mistakes because we’ve spent 15 years reading the specific ways this town’s microclimate attacks buildings. Led by Russ Delmar, our crew walks every Sausalito site with a corrosion and drainage checklist before quoting.
Second, we put everything in writing before work starts. The written price covers the coastal-spec materials, the engineered foundation, the permit fees, and the labor. The Kingswell Guarantee travels with every project: if it’s not done right within 365 days, we come back and fix it, free.
Third, a live person answers when you call (707) 760-0502. Not a chatbot, not a voicemail tree. You ask about your estimate, your schedule, your guarantee, and a human picks up. Day or night. Russ Delmar’s direct line is on every written contract for Sausalito jobs.
Room Addition Contractor in Sausalito
A Room Addition Contractor in Sausalito deals with a housing stock that was largely built between 1920 and 1965, on lots that slope 20 to 40 degrees, with almost no flat buildable space left. The typical ground-level addition here means cutting into a hillside, pouring a stepped or cantilevered foundation, and managing drainage from the uphill neighbor’s runoff. That’s not a generic room addition. It’s a hillside engineering project with a bedroom attached.
What a Sausalito Room Addition Includes
Every room addition we build here starts with a soil report, a structural engineer’s foundation design, and retaining-wall calculations. On streets like those above Hurricane Gulch, the framing is 2×6 or 2×8 rather than standard 2×4, simply to carry the shear loads from wind off the bay and the weight of the roofline against the slope. Expect helical piers or caissons if the soil is soft clay or fill, which is common on the flatter lots near Caledonia Street and along Bridgeway.
Cost Realities for Room Additions Here
A single-room bump-out addition in Sausalito runs $180,000 – $280,000 at the economy finish level and $280,000 – $420,000 for mid-to-high-end finishes, with the foundation and retaining wall eating 30 – 40% of that budget before a wall goes up. If your lot sits in a liquefaction zone near the waterfront, the foundation engineering alone can add $18,000 – $35,000. We don’t pad these numbers. We show you the soil report and the engineer’s calc, then price exactly what the stamped drawings require.
Second Story Addition Contractor in Sausalito
A Second Story Addition Contractor in Sausalito has to contend with 1920s – 1950s homes that were never framed, bolted, or sheathed to carry a second floor, plus the architectural review boards that care deeply about the hillside streetscape. Second-story additions here are the most expensive per square foot of any addition type, and the most likely to be rejected at the planning counter if the design ignores the neighborhood’s historic character.
Why the Structure Matters More Here
In the flats of Corte Madera or San Rafael you can sometimes reuse the existing first-floor framing. In Sausalito you almost never can. The original studs are undersized, the sill plates sit directly on concrete with no capillary break, and sixty years of marine moisture has usually compromised the rim joists. We plan for full first-floor structural upgrades, which means the project isn’t just a second story. It’s a down-to-the-sill retrofit that happens to end up as a second floor.
What a Second Story Costs
A second-story addition in Sausalito runs $350,000 – $700,000. That includes the structural upgrade to the first floor, shear walls or steel moment frames for lateral resistance, and the architectural review package. Coastal-spec hardware, which you cannot skip here, adds 8 – 15% to material costs compared to an inland job. That difference is the reason you’ll see bids from inland contractors that look cheaper on the surface. They’re using the wrong spec, and you’ll pay for it in a decade.
Trusted Brands We Service in Sausalito
We stock and install materials from the brands that hold up in Sausalito’s salt air, and we keep a local parts inventory so your project doesn’t stall waiting on a shipment. For siding on hillside additions we specify James Hardie fiber cement: it doesn’t warp in marine moisture and it takes paint on the marine coat schedule without blistering. For a detached ADU built by Sausalito specialists or a fast-framed bump-out, we work with Abodu and Cover prefab systems, which get closed in quickly before the fog settles into the framing. Tuff Shed structures get upgraded here: we replace their standard galv hardware with 316 stainless on install day, because their stock fasteners rust through within five years facing the bay.
Common Home Addition Contractor Problems We See in Sausalito Homes
- Electro-galvanized fasteners rusting to failure. Standard zinc-plated screws and bolts last about five years in Sausalito’s marine air. We remove them from failed additions and ledger connections around Hurricane Gulch and replace them with 316 stainless or hot-dip galvanized, which lasts decades.
- Unsealed pavers and patios wicking moisture into lower-level rooms. The consistent damp here causes efflorescence to climb through paver joints and press moisture against foundation walls. We seal every paver joint with polymeric sand and install capillary breaks between the concrete and the framing.
- Mold in carved-in-hillside rooms. A lower-level addition cut into a Sausalito slope needs cross-ventilation and a full moisture barrier, or black mold shows up within two winters. We see this in the partial-basement additions off steep streets like those near Hurricane Gulch.
- Ledger rot from missing peel-and-stick membrane. On hillside additions, the ledger connects the addition to the existing house. Skip the waterproofing behind it and the rim joist rots from the inside out. We rebuild the connection with copper naphthenate-treated lumber, stainless bolts, and a full flash-and-membrane detail.
Pricing for Home Addition Contractor in Sausalito, CA
Ground-level room additions in Sausalito run $180,000 – $420,000. Second-story additions run $350,000 – $700,000. Bump-outs run $90,000 – $150,000 if the foundation is grade-adjacent and the hill isn’t severe. Garage additions or conversions run $140,000 – $260,000. The single biggest variable is whether your lot requires retaining walls, helical piers, or a cantilevered foundation, and the second biggest is the hardware spec, which we never compromise on. The Kingswell Guarantee means the written price you get before work starts is the price you pay. Written guarantee included. Call (707) 760-0502 for a free on-site estimate and a line-item breakdown.
We Also Serve Cities Near Sausalito
If you’re on the edges of Sausalito, we serve Corte Madera, San Rafael, San Francisco, and Richmond with the same coastal-spec and written-guarantee standards. A Sausalito job might involve a hillside near Bridgeway or a small lot near Caledonia Street. Wherever the parcel sits, the same crew standards and Home Addition Contractor in Sausalito pricing apply.
Serving Sausalito, CA - Our Local Coverage Area
We’re based in the Sausalito area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs About Home Addition Contractor in Sausalito
Because standard galvanized hardware rusts through in roughly five years in Sausalito’s salt air, and coastal-spec 316 stainless or hot-dip galvanized costs 2.5 to 4 times as much up front. The material line on a hillside addition might jump from $4,000 to $11,000. That’s not markup. That’s the cost of not rebuilding your ledger in year seven. Call (707) 760-0502 for a written quote that itemizes exactly which steel sits in which location.
Most steep-slope additions in Sausalito require caissons or helical piers, engineered retaining walls, and a stepped footing that follows the grade, engineered and stamped by a structural engineer. The county planning review triggers this requirement automatically on slopes over 20%. The foundation alone on a 400-square-foot room addition can run $60,000 – $110,000 depending on soil and slope. We don’t guess at this number. We pull the soil report and show you the calc.
We install a full capillary break, an interior drain mat against the block or concrete, and cross-ventilation in every below-grade wall, plus we seal paver joints outside and slope finish grade away from the foundation. Musty smell in a Sausalito lower-level addition is almost always trapped marine moisture behind drywall, and it’s preventable with the right vapor management. If you’re pricing a lower-level addition, ask for the ventilation schedule in writing. We’ll put it in the estimate. Call (707) 760-0502.
Yes. We work with the Sausalito design review process and stay within the hillside streetscape guidelines, matching roofline pitch, window proportions, siding profile, and eave detail to the original home. That’s not optional. The review board will reject a flat-roofed box on a 1930s stucco cottage. We build additions that read as original construction from the street and still meet current seismic code. Bring us a photo of your house and we’ll show you what’s approvable.
They make material delivery a rolling puzzle. On streets like those off Hurricane Gulch, full-size lumber trucks cannot turn, so we schedule relay loads to a flat yard and deliver in smaller trucks, which adds $3,000 – $8,000 to the project depending on access. We coordinate with neighbors for temporary right-of-way and schedule pours when the road is least congested. This is normal to us. It will blindside anyone from out of town.
Written by Russ Delmar, Owner at Lodgewick ADU San Francisco, serving Sausalito since 2010.
