Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
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Before
AfterFast, Reliable Home Additions & ADU Across Los Altos
Home additions and ADU construction in Los Altos typically run $45,000-$130,000 for room additions and $90,000-$220,000 for detached ADUs, with timelines driven by the city’s Architectural and Site Review process and long-lead custom materials rather than labor alone. Our crews serve Los Altos from our San Francisco Bay Area dispatch office, and we’ve delivered 4,000-plus projects since 2007 with a written price before any work starts, every time. Call (669) 202-9618 to schedule your free estimate and get a line-item quote you can screenshot and compare.
Why Rowan Construction Group Cupertino Is Los Altos’s Preferred Home Additions & ADU Company
We’ve worked Los Altos long enough to know that a contractor who treats this city like Sunnyvale or Santa Clara will miss the ASR design-review layer and lose two to four months before permit submittal. Our Home Additions & ADU team has navigated the Architectural and Site Review process on multiple projects in North Los Altos, South Los Altos, and the Loyola Corners area, and we build that timeline into every schedule we write.
Our customers here read the three-star reviews before they call. They want the price range on the page, a written scope before anyone picks up a tool, and a photo record of what happened when the crew left. Under Clause 1 of The Haven Standard, the price is written before any work starts. Under Clause 3, no change proceeds without a signed change order. That’s the discipline that has kept our projects within a few percent of the agreed cost across 4,000-plus jobs since 2007.
A live person answers our phones 24/7. Our technicians are background-checked and uniformed. Every visit includes a documented photo record as standard, not an upgrade. And our 365-Day Done Right Promise is printed on every page, backed by a terms page you can read, not an asterisk.
Our Home Additions & ADU Services in Los Altos
New Detached ADU
Detached ADUs in Los Altos are typically scoped at maximum buildout under the city’s FAR and height limits because land values here, $2.5M-$4M on a typical parcel, make every square foot economically significant. We frame these on slab-on-grade foundations with the September-October pour window in mind, scheduling excavation and grading to beat the November-April rains that stalled projects across the city in 2022-23. The custom KraftMaid cabinetry and Cambria quartz for the kitchen are ordered the week the scope is signed, not after demo, because lead times drive the calendar on this tier.
Second Story Additions
Adding a second story to a 1950s post-and-beam ranch in Los Altos means dealing with original cast-iron drain lines, knob-and-tube-era electrical panels, and undersized subpanels that require full upgrades under permit. We assess these conditions during our first site visit and write them into the scope, so the price you agree to includes the work that actually needs doing. The ASR process scrutinizes massing and roofline compatibility, so we coordinate with your architect early to avoid redesign delays.
Room Additions
Rear and side room additions on Los Altos ranch homes require careful sequencing around the existing slab foundation and the mature oak canopy that the city protects. We handle the site prep, utility rough-in, and foundation work as a single phase, then run framing and dry-in on a schedule that accounts for the custom millwork lead times. Our documented photo record tracks substrate conditions, moisture readings, and structural connections at every stage.
Garage Conversion ADU
Converting a garage in Los Altos runs $30,000-$80,000 and involves more than drywall and a kitchenette. The existing slab often needs moisture mitigation, the electrical service requires upgrading from the original 100-amp panel, and the ASR review applies to any substantial alteration of the exterior envelope. We pull permits, coordinate inspections, and deliver a written price that includes these realities, not a low opener that balloons after demo.
Junior ADU & Interior Conversion
Junior ADUs, created within the existing footprint of a Los Altos home, avoid some ASR complexity but still require fire separation, independent egress, and kitchenette plumbing that the original 1960s drain lines were never sized for. We scope these with a camera inspection of the waste lines and a load calculation on the electrical panel, so the written quote reflects the actual infrastructure.
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.
Before
AfterTrusted Brands We Service in Los Altos
We source across fifty-plus vetted brands so our written quotes carry honest numbers rather than inflated ones. For Los Altos ADU and addition kitchens, we regularly specify KraftMaid and Wellborn cabinetry, Cambria and Caesarstone countertops, and Kohler and Toto fixtures. On exterior elements, we’ve installed ViewLux architectural windows and Barrette aluminum railing systems on custom builds from North Los Altos to the Foothill Expressway corridor. Our relationships with these suppliers mean we can lock in lead times at contract signing, not chase availability after the frame is up.
Common Home Additions & ADU Problems We See in Los Altos Homes
- Starting an addition in October without a locked-in dry-in date. A heavy rainy season like 2022-23 stalls excavation and foundation pours across a small contractor pool, and the project sits open to the weather. We schedule backwards from the pour window and confirm subcontractor availability in writing.
- Treating Los Altos ASR like Sunnyvale or Santa Clara permitting. The Architectural and Site Review layer scrutinizes massing and rooflines and can add two to four months before a permit is even submitted, wrecking a schedule that assumed a fast turnaround. We build this into every timeline we present.
- Ordering long-lead custom millwork and architectural glass after demo instead of at contract signing. Lead times, not labor, drive the calendar on this tier, so late orders push the punch list into the next rainy season. Our scopes include procurement milestones with supplier confirmation dates.
- Undersized electrical and plumbing infrastructure in 1950s-1970s ranch homes. Original cast-iron drains and knob-and-tube-era panels require full upgrades that many scopes omit. We camera the lines and load-calculate the panels before we write the price.
Pricing for Home Additions & ADU in Los Altos, CA
A typical home addition in Los Altos runs $45,000-$130,000, ADU construction runs $90,000-$220,000, and garage conversions run $30,000-$80,000. These ranges reflect the high-end finishes and custom millwork standard in this market, not builder-grade materials. What moves a project within or above these bands is the condition of the existing infrastructure, the complexity of the ASR design-review path, and the specification level of the finishes, not our labor rate.
| Service | Price Range in Los Altos |
|---|---|
| Home Addition | $45,000-$130,000 |
| ADU Construction | $90,000-$220,000 |
| Garage Conversion | $30,000-$80,000 |
Every quote is a flat price with a written scope and written warranty. No change proceeds without a signed change order. Bring a competitor’s written estimate and we’ll review it line by line at no charge. Call (669) 202-9618 for your free estimate.
We Also Serve Cities Near Los Altos
Our crews work throughout the mid-Peninsula, including Home Additions & ADU in Los Altos and surrounding communities. We regularly coordinate projects in Mountain View, Palo Alto, Menlo Park, and Sunnyvale, though each city’s permitting timeline and design-review requirements differ from Los Altos’s ASR process. The written scope we deliver accounts for these local variations.
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 - Home Additions & ADU in Los Altos
The Architectural and Site Review process in Los Altos typically adds two to four months before a permit can even be submitted, because the city scrutinizes massing, rooflines, and neighborhood compatibility on every custom build. This is a design-review layer that contractors accustomed to Sunnyvale or Santa Clara’s more streamlined permitting are regularly caught off-guard by. We build this timeline into every schedule we write and coordinate with your architect early to avoid redesign loops. Call (669) 202-9618 to discuss how ASR timing affects your specific project.
Lead times on custom KraftMaid cabinetry, Cambria quartz, and architectural glass, not our crew availability, set the completion calendar on Los Altos ADUs. Ordering these materials at contract signing locks in supplier slots and delivery dates that would otherwise push finish work into the November-April rainy season. Our field vignette: on a 1950s post-and-beam ranch off Lincoln Avenue in North Los Altos, we ordered the ADU kitchen millwork the week the scope was signed, ran underground utilities and subfloor work in parallel, and had the frame ready when the cabinetry landed. Late orders mean late delivery, and late delivery means weather risk. Call (669) 202-9618 to schedule your free estimate.
We do not schedule foundation pours for Los Altos additions between November and April if it can be avoided, because the concentrated rainy season creates a hard scheduling crunch and a heavy season like 2022-23 can stall multiple projects simultaneously across a small city with limited contractor capacity. We target September-October for excavation, grading, and pours, and we confirm dry-weather backup dates with our concrete supplier in writing. If you’re considering a winter start, call (669) 202-9618 and we’ll review the specific site conditions and weather contingencies.
A Los Altos homeowner should expect $45,000-$130,000 for a room addition, $90,000-$220,000 for a detached ADU, and $30,000-$80,000 for a garage conversion, with the final number driven by existing infrastructure condition, ASR complexity, and finish specification rather than labor rate. Because Los Altos land alone clears $2.5M-$4M, additions here are almost always scoped as maximum-buildout custom work under FAR and height limits, not incremental square footage. Our written quote includes every line item, and our Free Second Opinion offer lets you compare our scope against any competitor’s. Call (669) 202-9618 for an exact quote, estimates are free.
Yes, we pull all permits and coordinate inspection sign-off for Los Altos ADUs and second-story additions, including the ASR design-review phase, building permit submittal, and final occupancy inspection. We do not hand off a set of plans and expect the homeowner to navigate the city; our project manager tracks the permit status and schedules inspections around the crew’s work sequence. The documented photo record we deliver at completion includes permit cards and inspection sign-offs for your files. Call (669) 202-9618 to schedule your free estimate and review our permit management process.
Ready to get a written price before anyone picks up a tool? Call (669) 202-9618 to schedule your free estimate. We’ll review your site conditions, assess the existing infrastructure, and deliver a flat-price quote with a written scope and written warranty. Our 365-Day Done Right Promise applies to every project, and our Free Second Opinion offer stands for any written estimate you want reviewed line by line.
Written by Grant Rowan, Owner at Rowan Construction Group, serving Los Altos since 2007.