A free site visit, a check of what your lot allows and a written, line-item price.
Get your free estimateADU Company in San Mateo, CA
Most San Mateo homeowners we talk to are standing on a lot that hasn’t changed size since the 1950s, trying to figure out how to fit another home on it without losing the backyard. We’re Sutton ADU Builders, and we work with the older bungalows and ranchers that define this city. That means garage conversions, backyard cottages, and room additions that respect both the compact lots and the specific zoning rules San Mateo applies to them. If you’re weighing an ADU or addition here, call (831) 272-7212. We’ll walk you through what’s actually possible on your street before you spend a dollar.
Why San Mateo Homes Are Different
San Mateo’s housing stock runs older and smaller than most Bay Area buyers expect. Much of what we work on was built between the 1920s and 1970s, with a heavy concentration of post-war ranchers and pre-war bungalows sitting on lots of 5,000 to 7,000 square feet. That changes the math. On a compact lot, an attached ADU carved from an existing garage often makes more sense than a freestanding cottage, because a detached structure eats into what little yard remains. We’ve seen this play out consistently in neighborhoods like Shoreview, where the original garages are frequently too small and structurally dated to convert without a meaningful seismic retrofit. The city’s zoning rules add another layer: setback requirements (the required gap between your new structure and the property line) and lot-coverage limits vary by district, and they dictate whether a backyard ADU pencils out at all.
The climate is a genuine advantage. San Mateo’s Mediterranean pattern means cool, wet winters and dry summers, so ADU designs here don’t need the heavy insulation load that colder inland cities demand. But the damp winter months do require real attention to moisture management and ventilation. A poorly detailed wall assembly in a San Mateo ADU will show itself within two winters, which is exactly the kind of thing our 365-Day Done Right Promise is built to catch. Local teams who work this city regularly understand which details protect a build over the long haul, not just through inspection day.
Our Main San Mateo Services
The two calls we field most from San Mateo homeowners come down to adding space: expanding the footprint of the main house, or building a separate ADU on the lot. Here’s how each works here.
Home Addition Contractor in San Mateo
A home addition in San Mateo usually means extending a rancher sideways or pushing up into a second story on a lot that can’t accommodate a wider footprint. The pre-1970s construction we see across the city means structural work often includes bringing the connection point between old framing and new up to current seismic code. Damp-winter moisture management matters at the roofline junction too. We give you a written price before we start, with the scope spelled out in plain English. If you want to understand what an addition on your specific lot involves, see how a home addition works in San Mateo.
ADU Builders in San Mateo
ADUs in San Mateo fall into two camps: detached backyard cottages and garage conversions. The detached route works best when the garage is too far gone or too small, but it triggers setback and lot-coverage review that varies block to block. Garage conversions avoid most of that review but often inherit the framing problems of a 1950s or 1960s build. We work with prefab products including Abodu, Cover, and Tuff Shed where they fit the lot, and we tell you plainly when a site-built ADU is the better call. Read more about our ADU builds in San Mateo.
Room Addition Contractor in San Mateo
A room addition is usually about one specific need: a ground-floor bedroom for an aging parent, a dedicated home office, a larger kitchen. On San Mateo’s compact lots, these additions often extend toward the rear setback or convert underused patio space rather than pushing into the front yard. The pre-war bungalow stock near downtown often has foundation work involved before any addition can go up cleanly. Every room addition starts with a written price and the name and photo of the crew lead before anyone arrives. Get details on room addition work in San Mateo.
What happens when you call
- 1
A real person answersNo phone trees - you reach a local pro.
- 2
You get an upfront price rangeHonest numbers before anyone is dispatched.
- 3
A background-checked tech heads outLicensed & insured, dispatched right away.
- 4
You approve before work beginsNothing starts until you say go.
Brands We Service in San Mateo
We service and integrate the ADU and exterior product lines most relevant to San Mateo lots, including Abodu, Cover, Tuff Shed, and James Hardie cladding systems. Because we see these products in the field regularly, replacement parts and material lead times stay predictable, and we can tell you honestly whether a given system fits your lot or fights it. See our brands for the full picture.
Pricing for ADU Company in San Mateo, CA
| Service | Typical range in San Mateo |
|---|---|
| Detached ADU, site-built, 400 – 600 sq ft | $180,000 – $320,000 before site work |
| Garage conversion ADU, existing slab | $120,000 – $220,000 depending on seismic retrofit |
| Garage conversion ADU, slab replacement needed | Add $15,000 – $35,000 |
| Prefab ADU (Abodu, Cover, Tuff Shed) | Varies by model; installation adds $30,000 – $80,000 |
| Home addition, single-story bumpout | $250 – $450 per sq ft |
| Room addition, 200 – 400 sq ft | $60,000 – $150,000 |
| Seismic retrofit, older San Mateo garage | $20,000 – $50,000 |
| Foundation repair for pre-war bungalow | $12,000 – $35,000 |
| James Hardie siding, full exterior | $28,000 – $65,000 |
What pushes a San Mateo number up most often is the age of the structure you’re attaching to or converting. A garage from the 1940s with an unreinforced foundation can add significantly to the base price, and so can drainage work on lots that slope toward the house. Whatever the number, you get it in writing before we start, and it doesn’t change silently mid-job. The Threshold Standard means the price you approve is the price you pay.
Neighborhoods We Serve in San Mateo
Our crews work throughout San Mateo, from the flatlands near downtown up into the hillside neighborhoods where access and drainage add complexity. We know the difference between a Shoreview garage conversion and a Baywood lot with stricter setback realities. Because dispatch is local, we typically schedule an initial visit within a few business days of your call.
- Shoreview
- Baywood
- Aragon
- Beresford
- San Mateo Park
Service Area – Cities Near San Mateo
We also bring the same Threshold Verified crew standard to homeowners in nearby communities around San Mateo. If your project is in Belmont, CA, South San Francisco, CA, Brisbane, CA, or Redwood City, CA, call the same number and you’ll get a written price before any work begins on your lot too.
Serving San Mateo, CA - Our Local Coverage Area
We’re based in the San Mateo 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 Company in San Mateo
We typically schedule an initial on-site visit within a few business days of your call, depending on how many San Mateo projects are already in progress that week. Call (831) 272-7212 and we’ll give you a specific date on the phone, not a callback window.
Yes, in most cases. San Mateo applies its own setback and lot-coverage rules that vary by zoning district, so a project that clears state ADU law can still need local adjustments. We handle that review as part of the written price, including any revisions required before permits are pulled.
It applies everywhere we work, including every San Mateo project. The written guarantee covers defects in workmanship for one full calendar year from project completion. If something isn’t right, we return and make it right at no charge. Call (831) 272-7212 for details on what’s covered.
What happens when you call
- 1A real person answersNo phone trees - talk to a local adu pro.
- 2You get an upfront price rangeHonest numbers before anyone is dispatched. No surprises.
- 3We come out and measureLicensed & insured, at a time that suits you - the visit and the quote are both free.
- 4You get the price in writingLine-itemed, yours to keep, and nothing starts until you say go.
What San Mateo Customers Say
"Detached unit with a small kitchen and bath. Windows and finishes were nicer than I expected for the budget."
- Philip S."Straight answers on what we could and couldn't do on our lot."
- Edwin H."Every crew member was vetted and carried a badge, which matters when they are around your family for months. Tidy site every day."
- Daniel F.
