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 Hills
A typical home addition in Los Altos Hills runs $45,000-$130,000, while a detached ADU runs $90,000-$220,000. Most projects take 4-8 months from signed contract to final inspection, but the real calendar driver in Los Altos Hills is not our crew’s labor. It’s the sequential approval through the Town’s Architectural and Site Committee, the protected oak root-zone reviews, and the long-lead custom finishes that set the finish date. Call (831) 704-1211 and we’ll walk you through how we fix the price in writing before any of those clocks start.
We serve Los Altos Hills from our San Francisco Bay Area office, with crews that know the hillside terrain, the county permitting sequence, and the ASC design review that every addition and ADU must clear. Whether you’re expanding a 1960s ranch off Page Mill Road or building a detached unit on a graded parcel near the Skyline Ridge, we measure the site conditions first, quote a flat written price second, and never start work until the scope and number are signed.
Why Rowan Construction Group Campbell Is Los Altos Hills’s Preferred Home Additions & ADU Company
We’ve delivered home additions and ADUs across Los Altos Hills since our founding in 2007, and our record is documented: 4,000-plus projects, every one with a written price before work started and a photo record when the crew left. Los Altos Hills homeowners tend to research the way they buy appliances - they read the three-star reviews, they want the price range on the page, and they prefer a text confirmation to a phone promise. We built our process for exactly that customer.
Our crews are background-checked and uniformed; a live person answers calls 24/7. Under the 365-Day Done Right Promise backed by The Haven Standard, if it’s not done right, we make it right - the guarantee is printed on every page and backed by a terms page, not an asterisk. And our Free Second Opinion on Any Written Estimate means you can bring a competitor’s quote and we’ll review it line by line at no charge.
Response time to Los Altos Hills is typically same-week for initial site visits, though we won’t rush the measurement and documentation phase that protects your final price. Dispatch and scheduling are coordinated from our San Francisco Bay Area office, with local crews who understand that a pier-and-grade-beam foundation on a Los Altos Hills hillside is not the same build as a slab-on-grade in flat Campbell.
Our Home Additions & ADU Services in Los Altos Hills
ADU Design & Permitting
In Los Altos Hills, ADU design and permitting is a three-layer process: ASC design review first, then Santa Clara County building permit, then construction. We handle the full sequence, including the geotechnical engineering and hillside grading analysis that the town’s 1-acre minimum lots and steep topography make standard. Our drawings account for Chapter 7A fire-resistant exterior materials from the start, and we flag protected oak locations before the arborist review so your foundation layout doesn’t get redesigned mid-process. Under Clause 1 of the Haven Standard, the price is written before anyone starts - including the pre-construction design and permitting phase.
Garage Conversion ADU
Garage conversions in Los Altos Hills run $30,000-$80,000 and face a specific constraint: many garages sit on slopes with limited access for utility trenching, and the town’s oak preservation ordinance can place root zones right where you planned to run sewer or water lines. We verify the utility path on site before quoting, not after. The conversion still requires ASC approval, and we include that timeline in our written schedule so you’re not comparing our 8-week construction estimate to a competitor’s 8-week estimate that omits the 10-week permitting phase entirely.
New Detached ADU
New detached ADUs are the most complex addition type in Los Altos Hills, and the most rewarding. Our crew built a detached ADU on a graded parcel in west Los Altos Hills where the ASC approval and an arborist’s root-zone report had to be completed before the county would accept the permit application. We set the pier-and-grade-beam foundation, hydrostatic drainage, and the full rough-in behind the Chapter 7A fire-rated envelope, then pulled design-assist on the owner’s KraftMaid cabinetry and Cambria island tops - long-lead items that, not our labor, set the finish date. The price was fixed at contract signing; no change proceeded without a signed change order.
Junior ADU & Interior Conversion
Junior ADUs and interior conversions in Los Altos Hills often involve reconfiguring 1960s-1970s ranch layouts with load-bearing walls that weren’t designed for opening up. We verify wall structure, subfloor capacity, and hillside drainage impact before quoting. These projects still clear ASC review if they alter the exterior envelope or add square footage, and we build that timeline into every written scope.
Room Additions, Second Story Additions, Sunrooms & Enclosed Patios
Room additions and second-story additions in Los Altos Hills require the same geotechnical and ASC sequencing as ADUs, with the added complexity of tying into existing structure on hillsides that may have settled unevenly over fifty-plus years. Second-story additions in particular demand verification of the original foundation’s capacity for lateral loads on sloped terrain. Sunrooms and enclosed patios face Chapter 7A fire-rating requirements for any new exterior envelope in the Very High Fire Hazard Severity Zone. We document existing conditions with photos, quote a flat price, and fix that price in writing before ordering any long-lead materials.
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 Hills
We source across fifty-plus vetted brands, giving the written quote honest numbers rather than inflated ones. For Los Altos Hills additions and ADUs, that means KraftMaid and Wellborn cabinetry for kitchenettes and full kitchens, Cambria quartz surfaces for islands and counters, and James Hardie fiber-cement siding for Chapter 7A-compliant exterior envelopes. We don’t stock these in a warehouse - we specify them in the written scope, order on approved drawings, and track lead times so your finish date is set by material delivery, not by guesswork. The customer receives a documented photo record on every visit, included as standard, showing what was found and what was done.
Common Home Additions & ADU Problems We See in Los Altos Hills Homes
- Ordering custom cabinetry or architectural glass before ASC-approved drawings are issued. A Los Altos Hills homeowner selects KraftMaid cabinets with a 10-week lead time, then the ASC requires a window relocation that changes the kitchen wall layout. The cabinets arrive wrong. We don’t order long-lead items until drawings are ASC-approved and signed off.
- Missing a protected oak’s root zone during initial layout. The pier-and-grade-beam foundation or utility trench falls inside a protected zone, the arborist flags it, and the foundation must be redesigned. We survey oak locations before schematic design, not after permit submission.
- Pricing on budget numbers without verifying hillside structure and drainage. A second-story addition priced at $45,000-$65,000 becomes $85,000-plus when the load-bearing wall, subfloor, and hillside drainage require engineered solutions. We verify on site, then write the price.
- Underestimating the sequential permit timeline. Homeowners compare our quote to a competitor’s that assumes county permitting only, omitting the ASC review that adds 6-12 weeks before the county application can even be filed. Our written schedule includes both phases with realistic durations.
Pricing for Home Additions & ADU in Los Altos Hills, CA
These are the ranges we write into scopes for Los Altos Hills projects. Every quote is flat, line-itemed, and signed before work starts.
| Service | Price Range in Los Altos Hills |
|---|---|
| Home Addition | $45,000-$130,000 |
| ADU Construction | $90,000-$220,000 |
| Garage Conversion | $30,000-$80,000 |
What moves you within these ranges: hillside grading and retaining wall requirements, pier-and-grade-beam foundation versus slab, Chapter 7A fire-rated exterior materials, and the custom finish level - from standard KraftMaid cabinets to full design-assist millwork. The ASC review timeline and any arborist-mandated redesign are not cost adders if we catch them in pre-construction; they become expensive change orders if discovered after breaking ground. That’s why we don’t start without a signed scope and a signed price. Call (831) 704-1211 for your free estimate - we’ll measure the site, flag the constraints, and put the number in writing.
We Also Serve Cities Near Los Altos Hills
Our Home Additions & ADU crews work throughout the South Bay, including Campbell, Los Gatos, Saratoga, and Cupertino. Each city has its own permitting sequence and terrain constraints, and we adjust our written scopes accordingly. For homeowners in Los Altos Hills specifically, the ASC review and hillside conditions create a project type that flatland neighbors simply don’t face.
Serving Los Altos Hills, CA - Our Local Coverage Area
We’re based in the Los Altos Hills 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 Hills
Los Altos Hills requires ASC design review before the county building permit application can even be filed, a sequential step Palo Alto does not impose. Add the geotechnical engineering, hillside grading analysis, and potential arborist review for protected oak root zones, and a project that takes 4 months in flat terrain becomes 6-8 months here. Call (831) 704-1211 and we’ll map the real timeline for your specific site.
We handle the full ADU design and permitting sequence, including ASC submission, geotechnical coordination, and county building permit application. The homeowner reviews and approves each submittal, but we manage the process, the documentation, and the follow-through. Under Clause 1 of the Haven Standard, the price for this pre-construction phase is written before it starts, not billed hourly.
Hillside foundations, retaining walls, and engineered drainage systems are standard here, not optional. Chapter 7A fire-resistant exterior materials add material cost. And the ASC review process often requires design revisions that, if caught late, trigger change orders. We price these constraints into the original written scope so the final invoice stays within a few percent of the agreed number. Call (831) 704-1211 for a line-item quote.
We don’t order long-lead items until ASC-approved drawings are issued and signed. For the west Los Altos Hills ADU we completed, KraftMaid cabinetry and Cambria island tops were specified during design-assist, but ordered only after final ASC approval. The lead time was known, built into the schedule, and did not affect the finish date because we didn’t start the clock early. No work proceeds on a change until the change order is signed - the administrative discipline that has kept our projects within a few percent of the agreed cost since 2007.
Our punch list verifies that every item in the written scope is complete and documented: fire-rated envelope continuity at all penetrations, hydrostatic drainage test results, cabinet and counter installation per approved shop drawings, trim and paint coverage, and the full photo record delivered to the owner. Final inspection with the county follows only after our internal sign-off. The 365-Day Done Right Promise then covers anything found after move-in.
Ready to price your project? Call (831) 704-1211 to schedule your free estimate. We’ll survey your site, flag the Los Altos Hills-specific constraints, and put a flat written price in your hands before anyone picks up a tool.
Written by Grant Rowan, Owner at Rowan Construction Group, serving Los Altos Hills since 2007.