A free site visit, a check of what your lot allows and a written, line-item price.
Get your free estimateFast, Reliable ADU Builders Across Millbrae
Building an accessory dwelling unit in Millbrae means working with a builder who understands hillside setbacks, geotechnical reports, and older homes that hide surprises behind the drywall. Our ADU Builders team handles detached backyard units, garage conversions, and basement ADUs across Millbrae, from the flats near Broadway to the slopes above Taylor Middle School. We give you a written price before any work starts, and we put the 365-Day Done Right Promise in writing on every project. If you’re on a hillside lot near Mills High School and wondering whether your backyard can even support an ADU, call (707) 760-0502 and we’ll walk you through what’s possible.
Why Lodgewick ADU San Francisco Is Millbrae’s Preferred ADU Builders Company
Millbrae homeowners call us because we treat a hillside lot differently than a flat one. We know the city’s permitting office asks for geotechnical reports on slopes that a flat Peninsula city would approve without a second thought. We know that a 1950s rancher near Meadows School often has aluminum wiring and termite-damaged sill plates waiting behind the drywall. Our crews have worked in neighborhoods from Lomita Park to the El Rancho area, and we’ve learned to write allowances into contracts so those discoveries don’t derail a project.
Russ Delmar leads our team, and he’s built our process around one principle: put everything in writing before the work begins. That means a written price, a defined arrival window, and a written guarantee on every Millbrae project. A live person answers our phones 24/7, so when you have a question about your permit or your schedule, you reach a human being, not a voicemail.
Backyard ADU in Millbrae
Backyard ADU work in Millbrae typically means building a detached unit on a lot that slopes, drains, or both. On flat sections near Spring Valley Elementary, a standard detached studio or one-bedroom unit generally runs $180,000 to $320,000. On hillside lots above the BART station, where a geotechnical report and a retaining wall enter the picture, expect $250,000 to $420,000. The difference isn’t the size of the unit. It’s the soil work, the drainage design, and the structural upgrades the hillside demands.
Detached Units on Sloped Lots
Millbrae’s hillside ordinances often require a soils review before the first permit is issued, even for a small backyard unit. We bring in a geotechnical engineer early, design the retaining wall to also serve as a privacy screen where the city’s view-corridor rules allow, and write the soil-mitigation line items into your contract before you approve anything. That way the geotech report doesn’t become a surprise.
Prefab and Modular Backyard Units
For flat lots with clear crane access, we install prefab and modular units from Abodu and Tuff Shed. These typically run $160,000 to $280,000 installed in Millbrae, including foundation, utility hookups, and the permit set. For hillside lots, we work with Cover and James Hardie siding systems to get a weather-tight shell that handles the coastal fog without trapping moisture.
ADU Construction in Millbrae
ADU Construction in Millbrae almost always intersects with the age of the house. Many homes here were built between 1940 and 1970, which means cast-iron sewer laterals, aluminum branch wiring, and foundations that predate modern seismic codes. When we convert a garage or finish a basement into an ADU, we open the walls and find what’s actually there before we commit to a number. A garage conversion in Millbrae typically runs $140,000 to $260,000, while a full custom-built detached ADU runs $280,000 to $450,000 depending on hillside conditions and finish level.
Opening Up Older Millbrae Walls
This is where most remodel quotes move. Outdated wiring, undersized framing, failed waterproofing, and the code upgrades a permit triggers once walls are open. We handle it by inspecting first, writing a 10% contingency for unknown framing and electrical into the contract, and pricing any surprise as a fixed line-item change order you approve in writing before we touch another board. The Kingswell Way is simple: say the price before the work, show up in the window given, leave the place cleaner than we found it, put the guarantee in writing, and come back if it fails.
Permit-Ready Documentation
Millbrae’s building department wants to see a pre-construction sewer lateral inspection, a moisture vapor test for any below-grade living space, and structural calculations for hillside foundations. We prepare that documentation as part of the fixed price, not as an add-on. You’ll know what the city will ask for before we submit the permit set.
Trusted Brands We Service in Millbrae
We work hands-on with established ADU brands and materials so Millbrae homeowners don’t have to guess which systems fit their lot and budget. Our crews install Abodu and Cover prefab units on flat and moderately sloped lots. We use Tuff Shed structures for studio ADUs where a simple, weather-tight shell fits the scope. And we specify James Hardie siding on most of our Millbrae builds because it holds up to the coastal fog that rolls in off the bay. Since we stock common trim, flashing, and siding components at our Bay Area yard, we can turn around material runs to Millbrae quickly without waiting on a distributor.
Common ADU Builders Problems We See in Millbrae Homes
- Skipped sewer lateral inspections. Millbrae’s aging clay pipes often crack during excavation for a backyard ADU, and on a hillside lot a spot repair can run five times the original estimate because of the setback requirements. We inspect the lateral before we dig.
- Assumed-dry basements. A 1970s basement near the El Rancho area might look dry in August, but the coastal fog means moisture moves through those walls all year. We run a moisture vapor test before finishing any below-grade unit, and we install ventilation and barriers the city actually requires.
- Drawn-ignoring setbacks. Designers draw tuck-under ADUs without accounting for Millbrae’s required 4-foot retaining wall offset on steep lots. The permit gets rejected, and the owner loses months redesigning. We check setbacks before we draw.
- Aluminum wiring surprises. 1950s and 1960s ranchers throughout Millbrae, especially near Meadows School, still have aluminum branch wiring. A garage conversion that triggers a permit will also trigger a panel upgrade. We write that into the allowance up front so it’s not a shock when the wall comes down.
Pricing for ADU Builders in Millbrae, CA
Here’s what Millbrae homeowners should budget. A prefab studio ADU on a flat lot runs $160,000 to $240,000. A garage conversion into a one-bedroom ADU runs $140,000 to $260,000, with the higher end reflecting panel upgrades, seismic retrofits, and structural repairs to the existing footprint. A custom detached ADU on a hillside lot runs $280,000 to $450,000, including geotechnical work, retaining walls, and drainage. These are honest ranges based on what we’ve built in Millbrae. Soil conditions, foundation age, and the city’s hillside review process are the big movers. The written price you get from us before work starts is the price you pay, unless you approve a change order in writing. Call (707) 760-0502 for a free estimate specific to your lot.
Key Takeaways
- Flat-lot prefab ADUs in Millbrae start around $160,000; hillside custom units can reach $450,000.
- Millbrae’s hillside ordinances often trigger a geotechnical report before the first permit.
- Our written change-order process means surprises are priced and approved in writing before work continues.
- Every project includes the 365-Day Done Right Promise, in writing.
We Also Serve Cities Near Millbrae
Our Millbrae crews also cover Millbrae-adjacent communities along the Peninsula. When you call us from San Bruno, Daly City, San Carlos, or San Francisco, you get the same written price, the same arrival window, and the same written guarantee. The hillside rules differ slightly from city to city, but the process doesn’t change: inspection first, written allowance, fixed change orders, and a clean job site.
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 ADU Builders in Millbrae
Millbrae requires a 200-amp electrical panel upgrade on most garage conversions in homes built before 1980, along with seismic anchoring of the existing foundation and a pre-construction sewer lateral inspection. If we find aluminum wiring or termite damage when we open the walls, we write a fixed line-item change order and get your written approval before continuing. Call (707) 760-0502 and we’ll walk through what your specific garage conversion will trigger.
Yes, on most hillside lots above the BART corridor, Millbrae’s planning department requires a geotechnical report before a detached ADU permit is issued. The report typically costs $3,500 to $7,000 and drives the retaining wall and drainage design. We coordinate the engineer and include the cost in your written estimate before you commit.
We pause work, document the condition with photos, and email you a fixed line-item price for the repair before we touch another board. Our contract already includes a 10% contingency for unknown framing and electrical, so most of these discoveries fit within the original budget. You approve the change order in writing, and we continue on schedule.
Millbrae’s building code requires a moisture vapor test before finishing any below-grade living space, and the city flags missing vapor barriers on final inspection. We install a capillary break under the slab, a vapor barrier on the walls, and mechanical ventilation sized to the room. This is the single most common reason a Millbrae basement ADU fails its final inspection the first time.
Yes, and on steep lots near Mills High School it’s often the smartest use of the slope. Millbrae’s hillside ordinance requires a 4-foot offset between the retaining wall and the structure, and the wall design has to clear view-corridor review. We draw the wall to also serve as a privacy screen, and we submit both elements in the same permit set so you avoid a second review cycle.
If you’re weighing a garage conversion, a backyard ADU, or a tuck-under unit on a Millbrae hillside, call (707) 760-0502. We’ll give you a written price, a defined arrival window, and a written guarantee on the work. That’s The Kingswell Way, and it’s how we build in Millbrae.
Written by Russ Delmar, Owner at Lodgewick ADU San Francisco, serving Millbrae since 2010.
