CA License #1119373Licensed, Bonded & InsuredPowered by Future Generation ConstructionFuture Generation
San Mateo ADU Builder
Sacramento-built ADUs for the San Mateo backyard.
We're a Sacramento design-build crew that takes the bigger San Mateo jobs: Baywood Tudors, Hayward Park bungalows, Shoreview flats, Highlands hillside lots. Real craftsmanship at numbers worth the drive across the bridge.
Trusted by homeowners across Sacramento & surrounding areas.
ADUs in San Mateo — fast facts
County
San Mateo County
Region
Bay Area
ADU types we build
Detached, Attached, Garage Conversion, Custom
Contractor license
CSLB #1119373
Free estimate
(916) 677-9774
Last updated
San Mateo lots are not Sacramento lots
San Mateo lots cost more than the house
San Mateo flips what a Sacramento builder counts on. A flat 5,500 sq ft lot off Alameda de las Pulgas is a respectable parcel here, and the dirt under it costs more per foot than the structure on top, so you're pulling livable space out of ground that already costs a fortune. On the free on-site walk our PM tapes the real setbacks off the fence, never the assessor map, and checks whether the only route to the backyard is a 34-inch gap, because tight access means crane or hand-carry, priced honestly. Flat Aragon and Hayward Park lots give you room; North Central bungalow blocks and the Sugarloaf or Highlands hillside often don't.
Free on-site walk before a dollar gets committed
Real setbacks taped off the fence line, not the parcel map
Tight-access and hillside lots flagged up front: crane vs. hand-carry priced honestly
The San Mateo catch we won't sugarcoat
Bay mud on Shoreview, grade in the Highlands
The honest negative in San Mateo cuts two ways. On the bay side (Shoreview, the Bay Meadows blocks on the old racetrack, east toward the Marina Lagoon and 101) the ground is bay mud and fill: prone to liquefaction, chunks inside FEMA flood mapping, so you need a geotech report and sometimes piles or a stem-wall raised above base flood elevation, plus an elevation certificate. A flat slab that works in Hayward Park is wrong a mile east. Up into Sugarloaf, the Highlands, or steeper Baywood and Aragon it inverts to slope: a stepped or pier-and-grade-beam foundation, retaining, drainage, easily another $25K to $70K. We check the liquefaction, flood map, and grade for your exact parcel before design locks.
Bayside liquefaction, bay-mud and flood mapping checked for your exact parcel
Hillside stepped/pier foundations and retaining priced before design locks
Geotech and elevation certificate built into the schedule where they're actually in play
Permits, in plain English
A City of San Mateo permit, not the county
Your San Mateo ADU runs through the City of San Mateo, not San Mateo County, and the shared name trips people up. The city handles ADUs through its Building Division at City Hall on West 20th Avenue; the county only governs unincorporated land like North Fair Oaks and the coastside. We confirm which jurisdiction owns your exact parcel up front. California killed discretionary review for compliant ADUs, so there's no hearing over a sightline, but San Mateo is a thorough counter: even with the 60-day clock, corrections and flood and geotech review push realistic timing to about 10 to 16 weeks. We fight the wait with a complete in-house set, site, structural, Title-24 and MEP, the drafter answering each comment.
Permit pulled through the City of San Mateo Building Division: city project, not county
County vs. city jurisdiction confirmed for your exact parcel up front
Complete in-house set: site, structural, Title-24, MEP, corrections answered by the drafter
Real San Mateo numbers
What an ADU costs by the Bay Meadows Caltrain
Peninsula pricing is its own animal. In San Mateo a 612 sq ft one-bedroom detached ADU with mid-grade finishes runs roughly $360K to $450K all-in on a flat lot for 2025 into 2026, and a 988 sq ft two-bedroom lands closer to $515K to $650K. A bay-mud parcel near the Marina Lagoon that needs piles, or a steep Highlands lot that needs retaining, adds $25K to $70K in foundation alone. The rent is the point: a finished one-bed rents for about $2,700 to $3,500 a month, a two-bed $3,600 to $4,500, with the Caltrain line and the Bay Meadows and Hillsdale cores keeping demand thick. Every prospect gets a fixed-price proposal, itemized scope and financing available, after the free walk.
612 sq ft detached one-bed: roughly $360K–$450K all-in on a flat lot (2025–2026)
San Mateo one-bed ADU rents around $2,700–$3,500/mo; two-bed $3,600–$4,500
Fixed-price contract: itemized scope, financing available if you want it
ADU Services
Pick the ADU that fits your San Mateo lot
Detached, attached, garage conversion, or fully custom — we design, permit, and build every type of ADU under one roof in the Greater Sacramento Area. Tap a card for the details.
“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.
The City of San Mateo, in almost every case, and yes, the shared name confuses everyone. They're two separate offices. San Mateo is an incorporated city with its own Community Development Department and Building Division at City Hall on West 20th Avenue, and your ADU's permit, plan check, inspections, and utility sign-offs all run through the city. San Mateo County's building department only has authority over unincorporated land: North Fair Oaks, the coastside, and rural pockets outside the city limits. If your house sits on a San Mateo street with city sewer, you're a city project. We confirm which jurisdiction governs your exact lot on the first visit so a set never lands on the wrong counter.
Usually yes, but it's the first thing we check, because San Mateo lots run small-to-mid and the answer drives the whole design. State law lets you build a detached ADU up to 800 sq ft (and often larger) with reduced 4-foot side and rear setbacks, which is what makes tight Peninsula lots work at all. The real constraint is rarely the rule. It's the physical yard: how much flat usable space sits behind the house, whether the grade falls away on a Highlands or Sugarloaf lot, and whether the side-yard access is wide enough to get a crew and concrete back there. An Aragon or Hayward Park lot often has room to spare; a North Central bungalow block or a steep hillside lot can be snug. We tape your real setbacks, read the grade, and measure the access gap on the first walk so the floor plan fits the dirt you actually have.
It changes the foundation, and it's the first thing we look up for an east-side parcel. The bay side of San Mateo (Shoreview, North Shoreview, the Bay Meadows blocks on the old racetrack, the ground out toward the Marina Lagoon and 101) is bay mud and fill. It's soft, it holds water, and it's prone to liquefaction in a serious earthquake, plus parts of it sit in FEMA flood mapping. A mapped or poor-soil lot usually needs a geotechnical report and sometimes driven piles or a stem-wall with the finished floor raised above the base flood elevation, with flood vents and an elevation certificate. It's completely buildable. These units go up out there constantly. It just has to be designed to the real soil and elevation from the start. We pull the data for your specific lot on the first visit so the foundation is priced correctly, never sprung after a slab is drawn.
Yes, and the slope is the design problem, not a deal-breaker. A hillside lot in the San Mateo Highlands, Sugarloaf, or the steeper edges of Baywood and Aragon wants a stepped foundation or pier-and-grade-beam rather than a flat slab, usually some retaining, and extra grading and drainage so water doesn't undercut the pad. Steep lots often need a geotech report for the cut, and the concrete frequently has to be pumped uphill, which is a real line in the budget. We've built on grade and we price it honestly. Depending on how steep, that foundation and site work can add $25K to $70K over a flat-lot build. We read the grade on the first walk and tell you straight what the hillside is going to cost before you fall for a floor plan that assumes flat ground.
Because the Peninsula is its own cost world, top to bottom. Labor rates, material delivery, the price of working on small tight-access lots, bay-mud and hillside foundation work, and city fees all run higher in San Mateo than in the Sacramento region. A flat-lot 612 sq ft one-bed that might be in the low $200Ks inland runs roughly $360K to $450K all-in here. The flip side is the rent and the land value: San Mateo one-beds rent for $2,700 to $3,500 a month and the underlying lot is worth a fortune, so the investment still pencils even at full Peninsula build pricing. We're upfront about the number on the first visit, no bait-and-switch off an inland price sheet.
It shapes the design, and you want a builder who designs to it rather than fighting it. San Mateo Park and Baywood are the grand, tree-lined end of town: older Tudors, Spanish-revival and period-revival homes on bigger lots with mature, sometimes protected trees and a strong, watched architectural character. A compliant detached ADU is still your right under state law. It just reads best when the roof line, materials, and proportions respect the main house instead of looking bolted on, and when the foundation threads around the protected oaks and heritage trees rather than through their root zones. That can mean an arborist look and a more considered exterior. We map the significant trees and match the unit to the architecture from the first sketch, because in these blocks a sympathetic design is both an easier review and a better-renting unit.
On a friendly flat lot, budget about $360K to $450K all-in for a 612 sq ft one-bedroom detached ADU with mid-grade finishes, and roughly $515K to $650K for a 988 sq ft two-bedroom with upgraded finishes. The biggest cost drivers after size are the foundation and the location. A bay-mud parcel near the Marina Lagoon that needs piles and a raised floor, or a steep Highlands lot that needs retaining and a stepped foundation, can add $25K to $70K over a plain flat build, on top of any electrical panel upgrade and how tight your side-yard access is. You get a fixed-price proposal after the free walk, so the final number is locked before you sign rather than guessed at.
California puts a 60-day clock on the City of San Mateo to approve or return corrections on a complete ADU application, and discretionary review is gone, so there's no neighborhood hearing to derail you. That said, San Mateo is a thorough counter, and between corrections, flood and geotech review where it applies, design scrutiny in the older neighborhoods, and utility and school-fee sign-offs, realistic timing from signed contract to permit in hand runs about 10 to 16 weeks here, longer than a quiet Sacramento suburb. The main variable is how clean the drawings go in, which is exactly what an in-house plan set drawn by the people who answer the city's comments is for.
It can affect the design, not your right to build. The north and east end of San Mateo sits under SFO arrival and departure paths and close to Highway 101, and the city pays attention to interior noise levels for new living space in those zones. In practice that usually means the ADU's windows, walls, and ventilation are detailed to meet the interior-noise standard: upgraded glazing, proper insulation, sometimes mechanical ventilation so the unit stays quiet with the windows closed. It's a spec detail we handle in the plan set, not an obstacle. We flag whether your parcel falls in a noise-sensitive area on the first visit so the acoustic detailing is in the drawings and the budget from the start.
Yes, deliberately and for the right projects. We're a Sacramento design-build outfit, CA license #1119373, and San Mateo is roughly a 100-mile, just-under-two-hour run via I-80 to I-680 and across the San Mateo Bridge. We don't pretend that's around the corner. It's a real drive, which is why we take the larger San Mateo ADU jobs where homeowners want Sacramento-area craftsmanship and pricing discipline on a build that's worth the travel. A detached unit, a serious garage conversion, a hillside or bayside build that needs real foundation work: those justify the trip and get a steady crew presence, not a contractor who vanishes for two weeks. Call (916) 677-9774 and we'll talk through whether your project is the right fit.
Special Offer · Get Up To$5,000 OFFYour New ADU Build!
Build Your ADU for Less
Save up to $5,000 on your detached, attached, or garage-conversion ADU. Permits and design included.
We treat every home like it's our own — quality work, clear communication, and happy homeowners.
PaulOwner · Future Generation
7 min read1,641 words8 sections
Building an ADU in San Mateo: what a Sacramento contractor learned working the mid-Peninsula
San Mateo sits in the middle of the Peninsula, the bay on one side, the western hills on the other, Caltrain and 101 running the spine, and it does not build like the inland suburbs we call home. The east side is bay mud and flood mapping, the west side is steep hillside, the older neighborhoods watch their architecture, and the rents are among the highest in the country. One more thing trips everyone up: it's a City of San Mateo permit, not a county one, despite the shared name. We're a Sacramento design-build crew that takes the San Mateo jobs worth the drive across the bridge. Here's the honest version.
01Section
In San Mateo, location decides everything
San Mateo is the county seat and the biggest city on the mid-Peninsula, and the single most important fact about building here is its shape. The city runs from the bay shoreline on the east up into the wooded hills on the west, and that two-mile spread of terrain controls almost every decision an ADU forces. The east side is reclaimed bayland: soft mud, fill, flood maps. The west side climbs into Sugarloaf and the Highlands, where the ground tilts and a flat slab is a fantasy. In between sits the older, flatter heart of the city, the friendly building ground.
That range is why a single citywide price-per-foot number is close to meaningless. Out-of-town bidders assume San Mateo is one kind of dirt. It's three, and reading which one you're on before a floor plan exists is the whole game.
