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San Mateo · Custom ADU
A custom ADU drawn for a tight San Mateo yard.
Land is dear here and the lots are modest, so siting a bespoke unit is a tight-yard exercise. We draw it to your exact parcel and your family, then build it.
Trusted by homeowners across Sacramento & surrounding areas.
Custom ADU in San Mateo — fast facts
City
San Mateo
ADU type
Custom ADU
Contractor license
CSLB #1119373
Free estimate
(916) 677-9774
Last updated
Why custom in San Mateo
When a tight lot needs its own plan
A catalog ADU plan wants room to breathe — a flat, open rectangle of yard and generous setbacks. San Mateo rarely hands you that. Lots here are modest and land runs so expensive that every foot of yard is fought over, so a stock footprint either won't fit or wastes the corners it does land on. Push west toward Baywood and Aragon and the ground starts to roll; over by Shoreview you're closer to the bay and its soft soil. Drop a pre-drawn plan onto any of it and you'll trim the unit to nothing. Custom starts where the rectangle quits. We draw the footprint to the buildable area you actually have, to the grade, and to the house already on the lot.
Footprint drawn to a tight San Mateo back yard, not a generic pad
Sited around setbacks, the existing home, and a modest lot's real corners
The answer when no off-the-shelf plan fits the parcel you own
The design phase
Site walk to permit, drawn in-house
Custom lives or dies in the drawings, so we spend real hours there. It opens with a site walk and a measure-up — and on a cramped San Mateo lot, that visit matters more than the survey does. A survey won't tell you how a Baywood lot tilts toward the back fence, where the neighbor's setback pinches your side yard, or whether we're carrying lumber down a 3-foot gap between the house and the property line. That first walk reshapes the plan more often than not. Then concept sketches: you react, we revise. Most clients run two or three rounds, a few push to five. Once the layout locks we draw full construction documents and file with the City of San Mateo. Honest part — this front end runs 6 to 9 weeks before the counter even opens it.
Site walk and access study before a single line gets drawn
Tight side-yard access checked early, since the materials path is the problem
Full construction documents drawn in-house, then filed with the city
Matching the main house
Matching a Craftsman or Spanish-revival
A custom unit should look like it came off your house, not like it got parked behind it. San Mateo makes that specific, because the older neighborhoods carry real architecture. San Mateo Park and Baywood run to Craftsman and Spanish-revival — deep eaves and tapered porch columns on one, smooth stucco, low-pitched clay-tile roofs and arched openings on the other. Hayward Park and Aragon mix in plenty of mid-century. Drop a plain stucco box behind a 1920s Craftsman and it argues with the whole property from the street. So we pull roof pitch off your actual house, match the eave depth or the tile profile, carry the siding or stucco texture across, and keep the new unit's massing in scale. A copied stock elevation rarely belongs on a San Mateo Park lot. A drawn one does — and it appraises like it.
Craftsman eaves and tapered columns for San Mateo Park and Baywood
Spanish-revival stucco, clay tile and arches matched where the home calls for it
Roof pitch, eave depth and finish drawn to your specific house
Multi-gen + finishes
Multi-generational layouts done right
A lot of our San Mateo custom work is families solving one exact problem — a parent who wants their own front door, or an adult kid who priced Peninsula rent and decided the back yard beats a lease. The rent math out here is a different planet from Sacramento, which is exactly why these units pencil at all. That reshapes the plan. We draw zero-step entries, 36-inch doorways, curbless showers with grab-bar blocking already set in the walls, and a second primary suite so two generations each keep their privacy. The detached state ceiling is 1,200 sq ft, and custom clients tend to push right against it — at 1,150 or so you fit two real bedrooms, a full kitchen, and a proper living room. Then finish level: quartz, real oak floors, a tiled shower instead of a fiberglass insert. Custom is where the premium package gets drawn in on day one, not bolted on later.
“Every ADU we build is designed to add long-term value and open new possibilities for your property. Let's build something great together.”
— Tim, ADU Specialist
Custom Designs
Built to fit your property & needs
Turnkey Process
We handle permits, plans & everything
Built to Last
Quality craftsmanship that stands the test
Financing Made Simple
$0 Down Options. Build Now, Pay Over Time.
You shouldn't have to drain your savings to build wealth. We partner with trusted ADU lenders to find financing that fits — many homeowners build with little to nothing out of pocket.
Home Equity (HELOC)
Tap your existing equity at competitive rates — the most popular way to fund an ADU.
Renovation Loans
Finance the build against your home's projected after-completion value.
ADU-Specific Financing
Specialized lenders who underwrite based on the rental income your ADU will produce.
Cash-Out Refinance
Roll the project into a new mortgage and keep one simple monthly payment.
Estimate Your Monthly Payment
See what financing your ADU could look like — and how rental income can help cover it.
$180,000Loan amount
Credit Score
Very good · 700–739
Estimated Monthly Payment
$1,320/mo
At 7.99% APR over 30 years (illustrative)
Often offset by $2,000–$3,500/mo in rental income
No prepayment penalties with most partners
Pre-qualification with no impact to your credit
Illustrative only — not a loan offer. Actual rates and terms are set by third-party lenders based on your qualifications.
Service areas
Where we build
Headquartered in the Greater Sacramento Area and serving homeowners from the Sierra foothills down through the Bay Area. Don't see your city? We probably still get there — just ask.
The most common things Sacramento homeowners ask before starting an ADU project.
Custom is the priciest path, and the Peninsula pushes it higher than almost anywhere we work — I won't soft-pedal it. For 2025-2026 we're seeing finished custom detached units in San Mateo land roughly $427K to $740K-plus, depending on size, finish level, and how tight or sloped the site is. The lot is the big variable. A flat Shoreview or Hayward Park parcel is more straightforward; a Baywood lot with a grade and a 3-foot side-yard access path costs more to build because the materials have to come in the hard way. Add the seismic detailing the whole region needs near the active faults, plus San Mateo's high permit fees and slower review. The flip side is why owners build here anyway: Peninsula rents run far above Sacramento, steady and strong. Even a $600K-plus unit pencils out in a way it never would back home.
Fair question, and I'll be straight with you. We're based in Sacramento, about two hours from San Mateo. We're not the closest crew you can hire. We extend to the Peninsula for homeowners who want our craftsmanship and our pricing over a Bay Area outfit's quote, or for a larger custom project that's worth the roughly two-hour drive — and custom usually is, because the value sits in the design and the build quality, not in being ten minutes away. I'll be on your lot for the site walk, the foundation pour, the framing, and the key inspections. If your job is a small, simple unit on a flat lot, a San Mateo-local crew may serve you better and I'll say so. For a complex, tight-lot custom build, the right team beats the close one.
A stock plan is pre-drawn and repeated — faster and cheaper, because the design work is already done and it drops onto an open pad. Custom starts at zero for your parcel: our designer sizes and shapes the unit around the setbacks, the grade, the seismic engineering, the look of your San Mateo home, and exactly how the family plans to live. Custom costs more and takes longer up front. The reason to pick it is a one-off problem — a tight Baywood lot, a slope, mature trees or a pool in the way, a Craftsman main house you want matched, an accessible suite for a parent — that a rectangle off the shelf can't reach. If your lot were big, flat, and clear and your house ordinary, we'd happily steer you to stock and save you money. On a modest San Mateo lot, that's rarer than you'd think.
Longer than stock — that's the honest answer, and San Mateo's permitting is slower than the Sacramento suburbs we usually work in. Design and construction documents run 6 to 9 weeks. City of San Mateo review on a clean set often runs 10 to 16 weeks, longer if the lot has grade or soft-soil issues that pull in extra scrutiny. The build itself is usually 7 to 10 months for a custom detached unit, with a tight-access or sloped lot stretching it because the work goes slower when the side yard is 3 feet wide. Door to door you're looking at roughly 13 to 19 months. The slower city counter, the high fees, and tight-lot logistics are what push it past a flat-lot Sacramento job — plan for it from the start rather than getting surprised at month four.
It can, and on a custom job it's worth getting ahead of. Most of San Mateo is flat — San Mateo Park, Hayward Park, Hillsdale, Shoreview near the bay — but the land rolls into gentle hills toward the west, around Baywood and Aragon. A slope means the foundation has to step, and a tight lot means access is the real fight. The upside of custom here is genuine: because we're drawing from scratch, we design the unit and its foundation to the grade and the soil instead of forcing a flat-pad plan onto ground or a yard that won't take it. We check the slope, the side-yard width, and any trees or pool on the first visit, then draw the set to clear review rather than fight it. A catalog plan has no answer for a 3-foot access path. A drawn one does.
Usually, yes — but it's a tight-yard exercise, and that's exactly where custom earns its keep here. Land is expensive and lots are modest across San Mateo, so a stock rectangle either won't fit behind the house or leaves dead corners you paid dearly for. We start by mapping the buildable area after setbacks, then draw the unit to use every workable foot of it — sometimes an L-shape around an existing tree, sometimes a narrow footprint hugging one property line to keep open yard on the other. The 1,200 sq ft detached ceiling rarely fits a small lot anyway, so we'll often land a sharp 600 to 900 sq ft unit that lives bigger than its number because nothing's wasted. A catalog plan can't flex like that. On a tight lot it's the whole reason to go custom.
Heavily, and it should. The Peninsula sits near the region's active faults, and the bay-side soil around Shoreview is softer than the firmer ground inland. Building here means building for ground motion. On every custom unit we draw the shear walls, hold-downs, anchor bolting, and a foundation tied together so the structure rides a shake instead of coming apart in one. On a flat, firm-soil lot that's a well-detailed slab on grade. Closer to the bay, soft soil gets engineered for specifically, and on a western slope the seismic detailing compounds with the grade. A custom unit pours a brand-new foundation, which is the opportunity: we engineer it and the framing above to the soils report from the start. A stock plan drawn for a calm, flat site elsewhere doesn't carry this. A drawn set builds it into the structural drawings.
The permit goes through the City of San Mateo — it's its own incorporated city, so plan check and inspections run through the city's building and planning departments. One counter, high fees, slower review than the Sacramento suburbs. Power is PG&E. A custom unit's electrical service, any main-panel upgrade, the load calc, and the meter set all coordinate through PG&E, which in the Bay Area can be slow. An all-electric unit with a heat pump, an induction range, and maybe an EV charger pulls real load, so we size the service and line up PG&E early in design rather than at the end, where it stalls a final inspection. With the city counter already slow, getting the utility piece moving early is half of keeping a custom build on schedule.
State law caps a detached ADU at 1,200 sq ft, and custom clients often want to build near that ceiling — at 1,100 to 1,200 sq ft you fit two genuine bedrooms, a full kitchen, and a real living room. Whether your San Mateo lot has room to site a unit that size is the harder question, because lots here are modest and land is expensive. A deeper Hillsdale or Shoreview back yard might carry a larger unit; a tight Aragon or Baywood lot with a slope often tops out smaller once setbacks bite. That's not a loss — a well-drawn 700 or 850 sq ft custom unit on a small lot lives far better than a stock box of the same size. Attached ADUs follow a different size rule tied to the main house, so we'll run those numbers for your specific lot.
In-house. Our designer does concept, floor plans, elevations, and the full construction document set, and that same drawing carries straight into the build with no handoff gap. You're not coordinating a separate architect, a separate engineer, and a separate builder who all point fingers when the access tightens or the soils report comes back. One team owns the design and owns the result — which matters even more on a San Mateo custom job, where the field decisions on a tight lot and the back-and-forth with a slower city counter are constant, and someone needs to own them end to end.
Other services
Not quite the right fit?
Every Sacramento ADU project is different. Here are the other paths we build under one roof — and we're happy to talk through which one fits your lot best.
We treat every home like it's our own — quality work, clear communication, and happy homeowners.
PaulOwner · Future Generation
9 min read1,946 words8 sections
Custom ADU design and construction in San Mateo
Some San Mateo back yards just won't take a stock plan. A modest lot where land costs too much to waste a corner, a Baywood parcel that rolls toward the west, a Craftsman or Spanish-revival home you want the new unit to match, or parents moving in who need a place drawn around them — that's when you build custom. We're a Sacramento design-build crew (CA license #1119373) that extends to the Peninsula for owners who want our craftsmanship and value, draws a bespoke ADU for your exact lot, and builds it design through final inspection, one team the whole way. Call (916) 677-9774.
01Section
What actually makes an ADU custom
People throw "custom" around loosely, so let me draw the line. A stock or model ADU is a plan we've already drawn and built before — pick a size, maybe swap a finish, and it drops onto an open pad. Quickest, cheapest, and for a roomy San Mateo back yard with firm dirt and an ordinary main house, often the right one. We build those gladly. But it isn't custom.
Custom means the design starts at zero, on your parcel. Our designer takes the survey, the City of San Mateo setbacks, the soils, the grade, the seismic requirements, and how your family plans to live. Then a unit gets drawn that didn't exist until your lot called for it. The footprint bends to the buildable area. The foundation answers the grade and the soil. The roofline answers your house.
