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 San Carlos
Home addition work in San Carlos typically runs $180 – $420 per square foot depending on whether you’re adding a bump-out, a second story, or a detached ADU. Most projects take 10 to 20 weeks from permit to final inspection. If you’re weighing a bathroom or bedroom addition, call (707) 760-0502 and we’ll walk you through real numbers for your lot before you commit to anything.
San Carlos is not one-size-fits-all building territory. The flats near El Camino Real behave differently from the hillside parcels up around Club Drive and Crestview. We know the difference because we’ve framed, trenched, and pulled permits across San Carlos for years. That local familiarity matters when a county reviewer flags a septic setback on an acreage parcel or when a 1940s cottage in White Oaks needs seismic work before we can pour a foundation.
Why Lodgewick ADU San Francisco Is San Carlos’s Preferred Home Addition Contractor Company
Lodgewick ADU Builders is the ADU company of the Kingswell family, established in 2010. Russ Delmar runs our San Francisco Bay Area operations, and every San Carlos project operates under The Kingswell Guarantee: a written price before work begins, a defined arrival window, a clean job site, and a written guarantee on every job. If the work isn’t right within 365 days, we come back and make it right. That commitment is in writing on every project, not just promised over the phone.
San Carlos homeowners call us because we answer the phone 24/7 with a live person. No voicemail loops, no chatbots. When you have a question about your bedroom addition in the middle of a Tuesday afternoon or a Saturday morning, Russ or someone on his team picks up. That matters when you’re five weeks into a build and need a straight answer about the framing schedule.
We run background-checked, uniformed crews on every San Carlos job site. You’ll know exactly who is walking onto your property each morning. And because we work with local prefab and materials suppliers like Boxabl, Plant Prefab, and James Hardie, we can often shorten the timeline on a San Carlos addition without sacrificing the look your neighborhood expects.
Bathroom Addition Contractor in San Carlos
A bathroom addition in San Carlos typically runs $45,000 – $95,000 depending on whether you’re bumping out on a slab, adding above a crawl space, or building a second-floor bath over an existing room. The range swings on DWV line access, waterproofing, and whether your existing electrical panel has room for a new dedicated circuit. On older San Carlos homes with 100-amp panels, the panel upgrade often gets bundled into the same permit.
Slab-on-grade baths on flat lots
Many San Carlos ranch homes sit on flat, rectangular lots with slab foundations. Cutting into a slab means trenching for new waste lines, which adds $3,000 – $7,000 in concrete sawing and pipe work compared to a bath over a crawl space. We scope that before quoting so the written price you see is the price you pay.
Second-story baths in hillside homes
Up in the San Carlos hills, a second-story bathroom often means running a new vent stack and tying into an existing soil line that may not align with your addition. The county’s setback rules can also limit how far an upstairs bump-out can extend over a septic leach field. We verify all of that in the first site visit.
Bedroom Addition Contractor in San Carlos
A bedroom addition in San Carlos typically runs $60,000 – $130,000 for a ground-floor bump-out or $110,000 – $220,000 for a second-story addition that includes structural steel and a new staircase. Square footage, foundation type, and whether the bedroom requires a new egress window or door drive most of the cost. San Carlos bedrooms also need to meet California Title 24 energy standards, which means insulation and glazing upgrades on some older homes.
Ground-floor bedroom bump-outs in White Oaks
The 1940s cottages in White Oaks have charm and, in many cases, unreinforced brick foundations that require seismic retrofitting before any addition can be approved. We coordinate that retrofit with the structural engineer and fold it into the written quote so there’s no surprise change order after demo begins. Expect $8,000 – $20,000 for typical retrofit work depending on the foundation’s condition.
Bedroom additions over existing garages
Some San Carlos homeowners add a bedroom above an attached garage rather than taking yard space. That usually means reinforcing the garage ceiling joists, adding a shear wall, and sometimes replacing the garage door header. On hillside lots where flat yard space is scarce, this is often the smartest way to add square footage without fighting the slope.
Trusted Brands We Service in San Carlos
We work hands-on with established ADU and addition brands and materials, including Boxabl, Plant Prefab, and James Hardie. For San Carlos homeowners, that means faster lead times on prefab panels and siding that holds up against cool, wet winters and warm, dry summers. We keep local supplier relationships in the Bay Area so a replacement panel or a Hardie plank bundle doesn’t stall your San Carlos project for two weeks. When we quote a brand, we quote real availability and real delivery dates, not a catalog promise.
Common Home Addition Contractor Problems We See in San Carlos Homes
- Septic and well setbacks on acreage parcels. Many San Carlos hillside and acreage lots fall under San Mateo County permitting, not city residential review. A county reviewer may require a 100-foot setback from a leach field or a 50-foot buffer from a well head, which can shrink an ADU footprint or force a redesign.
- Older foundations that were never built for additions. Mid-century ranch homes and 1920s – 1950s bungalows often have unreinforced foundations. Before we can add a bedroom or bath, the footing may need seismic retrofit work, which changes both the timeline and the price.
- Narrow hillside driveways that trucks can’t navigate. Standard 48-foot trusses don’t work when the delivery truck can’t turn around on a long, steep driveway off Club Drive or Crestview. We scope access before quoting so you don’t pay for a crane reroute or a hand-carry charge later.
- Undersized electrical panels. Many San Carlos homes still run on 100-amp service. A bedroom or bathroom addition with new circuits, heaters, or an electric water heater will likely trigger a panel upgrade, which we fold into the written price up front.
Pricing for Home Addition Contractor in San Carlos, CA
Here’s what we tell San Carlos homeowners in plain numbers. A bathroom addition runs $45,000 – $95,000. A ground-floor bedroom bump-out runs $60,000 – $130,000. A second-story addition runs $110,000 – $220,000 depending on structural work and finish level. A detached 600 sq ft ADU on a half-acre parcel typically runs $180,000 – $260,000 when you factor in county septic and well setbacks, grading, drainage, and foundation work. The Kingswell Guarantee means you get a written price before any work starts. No price changes at the door, no change orders invented mid-build. Call (707) 760-0502 and we’ll give you a real number for your San Carlos lot.
One thing we always explain: a flat per-square-foot quote without a site visit is a guess. San Carlos hillside acreage parcels with county permitting requirements don’t fit a standard cost model. We visit, we measure, we check setbacks, and then we quote.
San Carlos’s County Permitting Reality and How We Scope Around It
San Carlos sits mostly within San Mateo County’s unincorporated permitting jurisdiction for many hillside and acreage parcels. That means an ADU addition on a larger lot often requires county-level septic and well setbacks rather than the city’s typical residential review, a hurdle that neighboring Belmont or Redwood City homeowners rarely face. If the main house is on city sewer but the parcel still has an old septic system within 100 feet of your planned addition, the county can knock your footprint down or require an alternative system.
Our crew recently framed a detached 600 sq ft ADU on a half-acre parcel off Club Drive near the San Carlos hills, where the county required a 100-foot setback from the existing septic leach field and a 50-foot buffer from the well head. Because the site had no paved turn-around, we scoped for a 40-foot material haul from the street and brought in a compact excavator for the new foundation, then coordinated with a soils engineer for the cut-and-fill drainage plan before quoting. That site visit, that scoping, is the reason the written price held through the entire build.
What changes the price on a San Carlos acreage addition: site access for concrete trucks and truss delivery, county septic and well reviews, grading and drainage corrections on sloped lots, and whether the existing foundation needs seismic work. We itemize all of it in the written quote so you see exactly what you’re paying for and why.
This is the Kingswell Way: say the price before the work, show up in the window given, leave the place cleaner than found, put the guarantee in writing, and come back if it fails within the 365-day period. On a San Carlos hillside lot, that promise means more because the problems that come up are the expensive kind. We’d rather scope them correctly on day one than hand you a surprise on day forty.
We Also Serve Cities Near San Carlos
Our crews work across the Peninsula, from Millbrae and San Bruno up through San Lorenzo and Daly City. If you’re in one of those communities and need a Home Addition Contractor, you’ll get the same written-price discipline and the same 365-Day Done Right Promise. Home Addition Contractor work across the Bay Area follows the same Kingswell standard, and our San Carlos team knows the local permitting offices and inspectors by name. Dispatch and scheduling are coordinated from our San Francisco Bay Area office; crews serve San Carlos locally.
Serving San Carlos, CA - Our Local Coverage Area
We’re based in the San Carlos 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 San Carlos
Yes, in many cases. If the parcel was ever served by a septic system, San Mateo County may still regulate setbacks from the old leach field even after the main house switched to city sewer. That’s why we pull county records before quoting any San Carlos acreage ADU. Call (707) 760-0502 and we’ll check your parcel’s history for free.
A concrete truck needs roughly 30 to 40 feet of clearance width and a firm, graded turn-around to pour a new foundation without a line pump. On narrow driveways off Club Drive and other hillside roads, we either schedule a line pump at $800 – $1,500 extra or order a shorter-boom truck. We verify access before we quote so the written price holds.
Most sloped San Carlos lots need a cut-and-fill plan with a retaining wall or a swale to move water away from the new foundation. A typical grading and drainage correction runs $5,000 – $25,000 depending on slope, soil type, and wall height. We bring in a soils engineer when the slope exceeds 10 percent, which is common in the San Carlos hills.
Often yes. Bedrooms need AFCI circuits, and a new addition with heaters, lights, and outlets can push a 100-amp panel past its limit. A panel upgrade to 200 amps runs $3,500 – $6,500 in San Carlos. We check your panel’s load during the first site visit and include the upgrade in the written quote if it’s required.
No, you should not build new square footage over an unreinforced brick foundation without a structural retrofit first. White Oaks has many 1940s cottages with brick foundations that don’t meet current seismic standards. We design the retrofit with a structural engineer, get it approved by the county, and then build. It’s the only way to pass inspection and keep the guarantee valid. For an exact quote on your San Carlos lot, call (707) 760-0502. Estimates are free.
Ready to get a real number for your San Carlos home addition? Call (707) 760-0502 and ask for Russ. He’ll schedule a free on-site estimate, walk the lot with you, and put the full scope and price in writing before you decide anything. The Kingswell Guarantee applies to every project we build in San Carlos, which means the price you see is the price you pay, and if it’s not done right within 365 days, we come back.
Written by Russ Delmar, Owner at Lodgewick ADU San Francisco, serving San Carlos since 2010.
