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 Millbrae
Building an addition onto your Millbrae home usually costs between $180 and $420 per square foot, with a standard 400-square-foot room addition landing between $72,000 and $168,000. Millbrae’s hillside lots, older mid-century foundations, and strict hillside ordinances mean the real wildcard is rarely the framing, it’s what the permit inspector finds once walls are open. We schedule every Millbrae addition with a pre-construction inspection so you know the full picture before we sign a contract, not after. Call (707) 760-0502 to get a written price for your addition before any work begins.
Key Takeaways
- Expect $180 – $420 per square foot for additions in Millbrae, with code upgrades adding $8,000 – $25,000 when old wiring or framing is exposed.
- Hillside lots in neighborhoods like Mills Estate and Taylor Terrace often need structural upgrades before the city signs off.
- Every Lodgewick project includes a written price, defined arrival window, clean job site, and a written guarantee, all before the first nail is driven.
- A live person answers our phones 24/7, including weekends, at (707) 760-0502.
Why Lodgewick ADU San Francisco Is Millbrae’s Preferred Home Addition Contractor Company
Homeowners in Millbrae keep calling us after another contractor walked away mid-project or handed them a change order that doubled the price. That’s the exact thing our Home Addition Contractor process is built to prevent. We put the price in writing before we open a single wall, and if the work isn’t done right, the 365-Day Done Right Promise means we come back and make it right, free, in writing, on every project.
Russ Delmar runs our team, and he’s the one homeowners in Millbrae talk to when they need a straight answer about their addition. We’re part of the Kingswell family of home-service companies, established in 2010, and we operate under The Kingswell Guarantee: written price first, real arrival window, clean job site, written guarantee on every job. Dispatch and scheduling are coordinated from the San Francisco Bay Area office, and our crews work locally in Millbrae, from Spring Valley to Lomita Park to the flats near the BART station.
What does that mean for a Millbrae homeowner? If we tell you a crew will arrive between 8:00 and 10:00 a.m., they arrive between 8:00 and 10:00 a.m. If we write you a price of $94,000 for a garage-to-ADU conversion, that’s the price. Background-checked, uniformed technicians show up at your door, and they leave the job site cleaner than they found it. That’s The Kingswell Way, and it’s why so many Millbrae homeowners who were burned before call us first now.
Second Story Addition Contractor in Millbrae
A second story addition contractor in Millbrae is what you need when your lot can’t grow outward but your family can’t fit in the footprint you have. On the hillside lots above Taylor Boulevard and along Magnolia Avenue, going up is often the only way to add real square footage without eating the yard. Expect to pay $220 – $420 per square foot for a second story addition in Millbrae, and time your project around the summer and fall months when fog and rain are less likely to slow framing and roofing.
What surprises Millbrae homeowners most is what the structural review turns up. A 1950s single-story rancher was never engineered to carry a second floor, so the plans often call for new footings, shear walls, or steel moment frames before the city will issue the permit. That’s not a change order surprise on our jobs because we price the structural allowance into the written estimate before you sign.
Foundation and Framing Upgrades
Older Millbrae foundations on hillside lots frequently need underfloor reinforcement, new anchor bolts, or full shear-wall upgrades before vertical load can be added. We inspect first, write the allowance in the contract, and any surprise found during demo is priced and approved in writing before we touch it.
Tying the New Story into the Old
Blending a second story with a mid-century roofline isn’t a cosmetic choice, it’s a structural one. We match the new framing to the existing plate lines and re-roof the entire structure so the addition doesn’t read like a box dropped on top. That also means one continuous roof warranty instead of a seam that leaks in the first heavy winter rain off the coastal hills.
Garage Addition Contractors in Millbrae
Garage addition contractors in Millbrae spend most of their time converting oversized two-car garages into livable space, because Millbrae’s mid-century homes were built with garages that typically run 400 to 600 square feet. A full garage conversion to a one-bedroom ADU in Millbrae runs $90,000 – $180,000, and the city’s ADU ordinance allows you to keep the existing structure while adding insulation, drywall, plumbing, and a proper kitchen and bath.
Millbrae’s location as a peninsula transit hub, anchored by the BART and Caltrain station, makes garage conversions especially attractive. High land values mean the cheapest new square footage is the garage you already own. But strict hillside ordinances and limited lot sizes turn every project into a tightrope walk between what you want to build and what the city will approve.
Garage-to-ADU Conversions
We convert oversized garages into full accessory dwelling units with their own entrance, kitchen, bath, and mailing address where the city allows it. Many Millbrae homeowners rent these units to commuters who want to be near the BART station, and the income often covers the construction loan payment.
Garage Additions and Bump-Outs
When you don’t need a full ADU, a garage bump-out adds 80 to 160 square feet for a workshop, home office, or extra bedroom without triggering the full ADU review. Bump-outs in Millbrae typically run $180 – $280 per square foot, and we handle the setback and daylight plane review for hillside lots.
Trusted Brands We Service in Millbrae
We work with established ADU brands and materials suppliers, and we match the right system to each Millbrae lot, budget, and timeline. For hillside garage conversions, we often use Boxabl or Plant Prefab panels because they arrive pre-cut and go up fast, which matters when fog and rain limit your workable days on exposed slopes. For siding that holds up to Millbrae’s coastal moisture, we specify James Hardie fiber cement. We keep common materials and hardware staged locally for Millbrae jobs, so a missing bracket or flashing detail doesn’t stall your project for a week. You don’t pay a premium for the brand names; you pay for whichever system actually fits your house.
Common Home Addition Contractor Problems We See in Millbrae Homes
- Knob-and-tube wiring behind the drywall. Millbrae’s 1940s and 1950s homes often still have original knob-and-tube circuits feeding bedrooms and garages. Once walls are open, the permit will not close until that wiring is replaced with modern Romex and a new sub-panel.
- Rotted sill plates from fog-driven moisture. Coastal fog wicks moisture up concrete stem walls and into the wooden sill plate it rests on. In below-grade and tuck-under spaces, that rotted wood has to be replaced and a moisture barrier installed before framing inspection will pass.
- Undersized footings on hillside lots. Many older Millbrae foundations were poured for a single story and a light roof. When you add a second story or a heavy tuck-under ADU, the city requires new rebar, deeper footings, or retaining work, and that work isn’t optional.
- Failed vapor barriers in basement and below-grade units. In a town where basements stay damp almost year-round, a missing or torn vapor barrier means mold, a failed inspection, and an untenantable unit. We install and test the barrier before insulation goes in, which is cheaper than tearing out moldy drywall later.
Pricing for Home Addition Contractor in Millbrae, CA
Millbrae additions run $180 – $420 per square foot, depending on scope. A simple 12-by-16-foot bedroom addition with no plumbing typically lands between $35,000 and $75,000. A second story addition on a hillside home with full structural upgrades runs $220,000 and up. A garage-to-ADU conversion ranges from $90,000 to $180,000, including a kitchen and bath. The biggest cost variable in Millbrae isn’t lumber or drywall, it’s what the permit inspection triggers once walls are open: rewiring, foundation work, and moisture mitigation. We price those as written allowances in the contract, so a surprise found during demo gets a signed, written change order before we proceed. Never a phone call asking for more money after the work is already half done. Call (707) 760-0502 to get your written estimate.
If you want to see a full written line-item price before you commit, that’s exactly how we work. The estimate is free, and it includes the structural and code allowances most Millbrae homes need. Call (707) 760-0502 and ask for Russ.
We Also Serve Cities Near Millbrae
Our crews work throughout the Peninsula. So if you own a home in San Bruno, Daly City, San Carlos, or San Francisco, you’ll get the same written price, defined arrival window, and written guarantee we give Home Addition Contractor in Millbrae customers. Call (707) 760-0502 and someone will answer in person.
Serving Millbrae, CA - Our Local Coverage Area
We’re based in the Millbrae 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 Millbrae
The permit will require replacing any exposed knob-and-tube wiring with modern NM cable and adding a new dedicated sub-panel if the existing panel is undersized. In Millbrae, that typically costs $8,000 – $15,000 depending on the panel and circuit count. The upgrade isn’t optional once the wall is open, which is why we write it into the structural and electrical allowance before you sign. Call (707) 760-0502 for an exact number on your house.
You get a written change order with the exact scope and price, and we do not proceed until you sign it. We build the most common surprises, framing, electrical, and waterproofing, into the contract as allowances up front, so the change order is smaller than you’d expect. If it’s something we should have caught in our pre-construction inspection, we eat that cost, not you. Call (707) 760-0502 to talk through your project before demo starts.
Yes, you’ll need a structural engineer’s stamp on any tuck-under ADU, and we coordinate that for you as part of the project. The hillside ordinances in Millbrae require engineered retaining walls, lateral bracing, and drainage details before the city will sign off on a below-grade unit. We work with local Millbrae engineers, so the plans come back approved faster. Call (707) 760-0502 and we’ll walk you through exactly what your lot needs.
Millbrae’s coastal fog keeps below-grade spaces damp almost year-round, even with our mild temperatures. Without a properly installed vapor barrier, that moisture condenses inside the wall cavity and feeds mold, and the city will fail your final inspection if it’s missing or installed wrong. We install and test the barrier before insulation, and we photograph it so you have proof when the inspector shows up. For a below-grade estimate, call (707) 760-0502.
Yes, Millbrae’s ADU ordinance allows garage conversions without requiring replacement parking if the lot is within a half mile of the BART or Caltrain station, and many Millbrae garages are close enough to qualify. Tuck-under designs also let you keep covered parking below while the ADU sits above, which is exactly what the hillside lots in Lomita Park and Mills Estate demand. We’ll check your parcel’s status before you commit to any design. Call (707) 760-0502 and we’ll pull the zoning for your address.
Ready for a written number instead of a guess? Call (707) 760-0502 to schedule your free estimate in Millbrae. Russ Delmar and our team will open the walls, show you what we find, and hand you a written price with every allowance included, before any work begins.
Written by Russ Delmar, Owner at Lodgewick ADU San Francisco, serving Millbrae and the Peninsula since 2010.
