Fast, Reliable New Detached ADU Across Los Altos
A new detached ADU in Los Altos typically runs $300,000 to $450,000 for a custom 1-bed or 2-bed unit, drawings through final inspection. The price is set in writing before any work starts, and it includes the permit set, the construction, and a documented photo record of every visit. If you’re weighing a backyard unit on a postwar ranch lot off Foothill Expressway or near Grant Park, call (971) 497-2402. We’ll walk the site, review your electrical service and roof condition, and give you a written scope with a fixed number.
Ellery ADU Studio operates as a design-build studio, and our New Detached ADU work in Los Altos is a single contract: one written price, one team, no designer pointing at the builder when something goes sideways. We know which Los Altos design-review overlays are still enforceable under state law and which ones were preempted by SB 9 and AB 2221. That distinction can save weeks at the permit counter.
Why Ellery ADU Studio Is Los Altos’s Preferred New Detached ADU Company
Since 2015, we’ve designed, permitted, and built more than 900 ADUs across the Bay Area, and Los Altos is one of the markets where our fixed-price model gets tested the hardest. The housing stock here is older than it looks from the street: single-story ranch homes built between 1950 and 1980, slab foundations, oversized two-car garages, and electrical panels that were marginal when they were installed. We quote with that reality on the table, not buried in the fine print.
Our Los Altos clients tend to be tech and professional families who bought between 2015 and 2025 and are now planning a high-end in-law suite, not a rental box. They want rift-sawn oak millwork, architectural glass, and a kitchen that matches the main house. They also want to know what the permit set will include before they sign. That’s how we work. Every project gets a written price under Haven Standard Clause 1, a photo record on every visit, and our 365-Day Done Right Promise in the contract.
When a homeowner near Loyola Corners calls us about a detached unit, we can usually be on-site within a day or two for the initial walkthrough. Scheduling is coordinated from our Bay Area office, but the crews who work Los Altos know the streets, the setbacks, and the quirks of the local building department.
Our New Detached ADU Services in Los Altos
Custom Built ADU
Most of our Los Altos work is fully custom. A typical project is a 750 to 1,000 square foot detached unit with one or two bedrooms, custom cabinetry, and a finish package matched to the main house. We start with the permit set, not a sketch. The drawings go to the city with structural calcs, Title 24 energy compliance, and a scope that’s locked at signing under Haven Clause 5. Custom millwork and specialty glazing get specified before we submit, because lead times on those items run 14 to 20 weeks in this market. You don’t want a Fleetwood slider package on order after the rough opening is already cut.
Prefab ADU Installation
For clients who want a faster path, we specify and coordinate prefab systems from Cover, Dvele, and Mighty Buildings within the same single contract. Prefab doesn’t mean off-the-shelf. In Los Altos, the site work still has to answer for the existing slab, the old electrical service, and the setback requirements on your specific lot. We handle the foundation, the utility connections, and the finish work so the prefab module arrives and becomes a permitted, completed ADU. The written price covers all of it.
Modular ADU
Modular construction can compress the build calendar, but the Los Altos permit process still runs on its own clock. We prepare the permit set for modular units the same way we prepare it for stick-built: full drawings, full energy compliance, full structural review. The difference is the factory-built shell. On a lot off Miramonte Avenue or Springer Road, a modular 1-bed can go from permit issuance to occupancy in less time than a full custom build, but the finish level is still yours to choose. We lock the spec before the order, so the price doesn’t drift.
Studio ADU
A detached studio ADU in Los Altos, typically 400 to 600 square feet, is the smallest permitted unit we build. It’s a genuine apartment: full kitchen, bathroom, separate entrance, its own address. On the ranch lots that dominate Los Altos, the studio often lands in the rear yard where the setback line and the mature oaks dictate geometry. We’re comfortable working with the city’s planning staff on that. The studio is also the most common choice for multigenerational families who need a space for an aging parent that isn’t a room in the main house.
What happens when you call
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A real person answersNo phone trees - you reach a local pro.
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You get an upfront price rangeHonest numbers before anyone is dispatched.
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A background-checked tech heads outLicensed & insured, dispatched right away.
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You approve before work beginsNothing starts until you say go.
Trusted Brands We Service in Los Altos
We specify and coordinate prefab and modular systems from Cover and Dvele, and we also work with Mighty Buildings panels when the project calls for them. The point isn’t the brand name on the module. The point is that the system arrives with a permit set that matches it and a written price that was set before we ordered anything. For Los Altos customers, that means no surprise upcharge when the panel spec changes or the delivery window shifts. Our contract is with you, not the factory.
Common New Detached ADU Problems We See in Los Altos Homes
- Undersized electrical service. Almost every 1950s-to-1970s ranch in Los Altos still carries a 100-amp Federal Pacific or Zinsco panel. A detached ADU with induction cooking and an EV charger needs a 200-amp service and a new underground feeder. We scope the panel replacement in the written price, not as a change order after demolition.
- Flat garage roof water intrusion. The original flat or low-slope roofs on 1960s homes frequently show deferred water damage that only appears once the conversion or new build starts. Los Altos winters bring atmospheric river events that test every parapet. We inspect the roof before quoting so the envelope is in the scope, not discovered later.
- Custom finish lead times. Specialty cabinetry, architectural glass, and custom door packages run 14 to 20 weeks in this market. If you order after the slab is poured, the schedule slips. Our fixed-price contract means we lock specs before we order, so the lead time is already counted in the calendar.
- Design-review confusion at the permit counter. Los Altos historically layered local design-review requirements on top of state ADU law. Many of those are now preempted by SB 9 and AB 2221, but not every staff member at the counter knows which ones. We do. That’s the difference between a three-week permit path and a three-month one.
Pricing for New Detached ADU in Los Altos, CA
A custom 1-bed detached ADU in Los Altos runs $300,000 to $380,000 for a design with mid-range finishes. A 2-bed unit with custom millwork, architectural glazing, and high-end kitchen finishes runs $380,000 to $450,000. Prefab and modular builds from Cover or Dvele typically land in the $280,000 to $360,000 range once the site work, foundation, and utility connections are included. Studio ADUs start around $250,000 and go up from there based on finish level.
What drives the number in Los Altos specifically is the existing service. The 200-amp panel replacement and new underground feeder are almost always required, and that alone is a $6,000 to $10,000 line item. The roof condition on the existing structure matters too. Every quote we write in Los Altos includes the written price before work starts, per Haven Standard Clause 1. Call (971) 497-2402 for a free estimate with a fixed number on paper.
We Also Serve Cities Near Los Altos
Our crews work throughout the mid-Peninsula. If you’re in Mountain View, Palo Alto, Menlo Park, or Sunnyvale, we bring the same fixed-price, one-contract model to your project. New Detached ADU in Los Altos remains our core focus, but the permit and design logic travels well across the 94022 and 94024 zips.
Serving Los Altos, CA - Our Local Coverage Area
We’re based in the Los Altos 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 - New Detached ADU in Los Altos
State law under SB 9 and AB 2221 preempts most local design-review requirements for ADUs, including Los Altos overlays that historically restricted height, rear setbacks, and architectural style. What still binds you are the objective standards in the Los Altos zoning code that the state hasn’t invalidated, plus the state building code. We prepare your permit set to the exact enforceable standard, so the city can’t bounce the application on a preempted requirement. Call (971) 497-2402 if you want us to review what’s actually binding on your lot.
The cost gap comes from land value, housing stock, and finishes. Los Altos lots sit in one of the nation’s highest residential land-value markets, and a permitted detached ADU can add $400,000 to $600,000 in appraised value. The housing stock is older postwar ranch, so a 200-amp panel replacement and full Title 24 envelope are almost always required. And the homeowner base here is building high-end in-law suites with custom millwork and architectural glass, not basic rentals. The product is different, so the price is different. Call (971) 497-2402 for a written quote specific to your lot.
You can, but you’ll add 14 to 20 weeks to the schedule and risk a price change. Custom millwork and specialty glazing in Los Altos run on long factory lead times that don’t start until the order is locked. Our fixed-price contract means we specify those items before we submit the permit set, so the order goes in early and the price is already in writing. That’s Haven Standard Clause 1 in practice. Call (971) 497-2402 to discuss your finish package before we draw anything.
Los Altos sits in a mild inland pocket with almost no freeze risk, but atmospheric river events bring weeks of persistent winter moisture. Flat roofs on 1960s homes frequently show deferred water intrusion that only surfaces during construction. For a new detached ADU, we specify low-slope TPO or standing-seam assemblies that handle the wet season without parapet leaks. If we’re converting an existing garage, we inspect the roof before quoting so any rebuild is already in the written price. Call (971) 497-2402 for a free estimate that includes the roof assessment.
Los Altos doesn’t require a separate meter for a detached ADU, but the city does require the existing service to handle the added load. In practice, almost every ranch home here has a 100-amp Federal Pacific or Zinsco panel that can’t support an ADU with modern appliances and EV charging. We upgrade to a 200-amp service and run a new underground feeder from the main panel to the ADU subpanel. The panel replacement and feeder are drawn, permitted, and priced in the original written quote. Call (971) 497-2402 to have your service evaluated.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Los Altos since 2015.