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AfterFast, Reliable Home Additions & ADU Across Los Altos
A typical home addition in Los Altos runs $45,000-$130,000, and an ADU construction runs $90,000-$220,000. Most projects require design review approval before permits are issued, so the calendar is set by long-lead millwork and architectural glass, not labor availability. Call (669) 259-1843 to schedule your free estimate with a written price before any work starts.
We serve Los Altos from our San Francisco Bay Area office, with crews dispatched to the North Los Altos, South Los Altos, and Loyola Corners areas regularly. The 94022 and 94024 zip codes are familiar territory - we’ve worked on the ranch-style slabs near El Monte Road, the Eichler clusters off Magdalena Avenue, and the larger lots up toward the Foothill Expressway corridor. Our Home Additions & ADU team knows the difference between a standard Santa Clara County permit package and what Los Altos’s own design review board will ask for.
Why Rowan Construction Group Santa Clara Is Los Altos’s Preferred Home Additions & ADU Company
We’ve delivered 4,000-plus projects since 2007, every one with a written price before work started and a documented photo record when the crew left. Los Altos homeowners find us the same way they research appliances: they read the three-star reviews, look for the price range on the page, and want a text confirmation of what was promised. We don’t do “call for a quote” - Clause 1 of The Haven Standard says the price is written before anyone starts.
Our crews are background-checked and uniformed; a live person answers calls 24/7. The 365-Day Done Right Promise is printed on every page, backed by a terms page, not an asterisk. If it’s not done right, we make it right.
Response time to Los Altos is typically same-week for initial consultation, with estimates delivered in writing within a few business days after site measurement. We don’t promise speed we can’t document.
Local knowledge matters here because Los Altos is not Mountain View. The city imposes its own design review for height limits, FAR caps, and neighborhood compatibility - a layer of scrutiny that adds time but also protects property values. Contractors who treat Los Altos like any other Santa Clara County permit jurisdiction end up re-submitting plans.
Our Home Additions & ADU Services in Los Altos
ADU Design & Permitting
ADU construction in Los Altos runs $90,000-$220,000. We handle the full permit package, including the city’s design review submission, which enforces 28-foot height limits and floor-area-ratio caps that neighboring jurisdictions don’t apply with the same rigor. Our drawings account for Los Altos’s specific compatibility standards from the first draft, not after a rejection. We coordinate with geotechnical engineers on the Santa Clara Valley’s montmorillonite clay soils - standard on most Los Altos flatland sites - so the foundation design is included in the initial quote, not added later.
Garage Conversion ADU
A garage conversion ADU in Los Altos typically costs $30,000-$80,000. Many Los Altos garages sit on the same post-tensioned or conventional slabs as the main house, with electrical panels originally sized for pre-HVAC, pre-EV-charger loads. We assess the panel capacity, the slab condition, and the fire separation requirements between dwelling units before quoting. On Eichler properties, we scan for embedded hydronic tubing before cutting into any slab - a step contractors unfamiliar with radiant-heat-in-slab construction sometimes skip.
New Detached ADU
New detached ADUs are among our most requested projects in Los Altos. The large lots - 8,000-15,000 sq ft is typical - create genuine opportunity, but the gap between land value and structure value means these projects are often evaluated against a full teardown-and-rebuild calculus. We help homeowners run that comparison honestly. Our quotes include deepened footings or post-tensioned slabs where geotechnical reports recommend them, and we lock the price in writing before ordering long-lead items like KraftMaid or Wellborn cabinetry, Cambria or Caesarstone surfaces.
Junior ADU & Interior Conversion
Junior ADUs work well in Los Altos’s single-story ranch stock, where a portion of the existing footprint is converted with a separate entrance. The 1950s-1970s electrical panels are the usual constraint - many are 100-amp services that need upgrading before a second kitchen and HVAC load is added. We identify this in the initial walkthrough and include it in the written scope, not as a change order surprise.
Room Additions & Second Story Additions
Room additions and second-story additions in Los Altos must navigate the same design review process as new construction. The 28-foot height limit is hard; second stories are feasible on many ranch profiles but require careful massing to pass neighborhood compatibility. We bring preliminary elevation studies to the first meeting so homeowners understand the envelope before committing to architectural fees. Second-story additions also require structural analysis of the existing foundation - the original post-tension or conventional slabs were engineered for single-story loads, and the Santa Clara Valley clay soils don’t forgive shortcuts.
Sunrooms & Enclosed Patios
Sunrooms and enclosed patios are smaller-scale projects that still trigger Los Altos’s design review when they exceed certain square footage thresholds. We handle the determination of whether a project needs full review or qualifies for an administrative approval, and we quote accordingly.
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, giving the written quote honest numbers rather than inflated ones. For Los Altos additions and ADUs, we regularly specify KraftMaid and Wellborn cabinets, Cambria and Caesarstone countertops, Kohler and Toto fixtures, and GAF or Owens Corning roofing where the design calls for conventional pitches. On fencing and hardscaping for ADU site work, we use Belgard and Techo-Bloc pavers. We don’t stock everything in a local warehouse - that would inflate overhead and, under Clause 1, the price - but we maintain relationships with regional distributors that keep lead times predictable. The brands are named in the written quote, with model numbers, so the customer knows exactly what the price covers.
Common Home Additions & ADU Problems We See in Los Altos Homes
- Ordering long-lead custom cabinetry or architectural glass before design review approval. Los Altos’s design review can take six to ten weeks, and if height or FAR comes back revised, the finish package ordered on optimism sits in a warehouse while the calendar slips. We don’t order until the city signs off.
- Treating an Eichler addition like a standard ranch. Cutting into the post-tension slab without locating embedded hydronic tubing severs the radiant heat system permanently. Stacking new load on post-and-beam walls that were never engineered for it risks structural failure. These homes require a specialist familiar with the Eichler system specifically.
- Standard shallow footings on montmorillonite clay without geotech review. The Santa Clara Valley’s expansive clay soils swell and shrink seasonally. An addition on standard footings moves independently of the original structure, and the drywall cracks, door binds, and punch list never really end. We bring in geotechnical reports as standard on Los Altos flatland sites.
- Electrical panels sized for 1960s loads. Most Los Altos ranch stock has 100-amp panels and minimal spare circuits. Adding a kitchen, HVAC, and EV charger to an ADU or addition without upgrading the service is a code violation and a fire risk. We assess the panel in the first walkthrough and include any upgrade in the written scope.
Pricing for Home Additions & ADU in Los Altos, CA
Here is what we see in the Los Altos market for projects quoted in 2024-2025. These are flat, written prices delivered before work starts, not estimates that shift:
| Project Type | Typical Range in Los Altos |
|---|---|
| Home Addition | $45,000-$130,000 |
| ADU Construction | $90,000-$220,000 |
| Garage Conversion ADU | $30,000-$80,000 |
What moves the number: foundation type (standard vs. post-tension vs. deepened footings on clay), whether the project clears design review on first submission or requires revision, and the finish specification. A kitchen-equipped ADU with Cambria counters and Wellborn cabinetry sits at a different point in the range than the same footprint with stock finishes. The price is fixed in writing before we order long-lead items, and no change proceeds without a signed change order - the discipline that has kept our projects within a few percent of the agreed cost across 4,000-plus jobs.
We also offer a Free Second Opinion on any written estimate: bring a competitor’s quote and we will review it line by line at no charge. Call (669) 259-1843 for your free estimate.
We Also Serve Cities Near Los Altos
Our crews work throughout the San Francisco Bay Area, with regular projects in Los Altos and neighboring Mountain View, Palo Alto, Menlo Park, and Sunnyvale. Each city has its own permit rhythm and design standards; we adjust the submission package accordingly rather than recycling the same drawings.
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
Los Altos’s design review process adds architectural coordination time, and the housing stock - Eichler slabs, post-and-beam walls, outdated electrical - requires specialized handling that standard ranch construction doesn’t. The finished product also typically specifies higher-grade materials. Call (669) 259-1843 for an exact quote on your specific project - estimates are free.
Yes, if the contractor knows the Eichler system. We scan for embedded hydronic tubing with thermal imaging before cutting any post-tension slab, and we design structural connections that don’t overload post-and-beam walls never engineered for additional load. We were called to an Eichler on the Los Altos flats to add a primary suite, and the first thing our tech did was scan for the embedded hydronic tubing in the post-tension slab before anyone touched a saw - cut that tubing and you’ve got a radiant-heat system with a permanent leak. We brought in a geotech report because the montmorillonite clay under those streets swells seasonally, deepened the footings, and set the subfloor over a post-tensioned slab tied to the existing post-and-beam walls, which were never designed to carry the new load. The new wing got Cambria counters and a Wellborn vanity, and the inspection sign-off cleared the rough-in before we closed the walls. Call (669) 259-1843 to discuss your Eichler project.
Materials and designer coordination, not labor. Long-lead custom cabinetry from KraftMaid or Wellborn, architectural glass, and specialty finishes typically drive the calendar. Labor is scheduled once materials are confirmed in-hand. We lock the price in writing before ordering to protect against lead-time inflation. Call (669) 259-1843 for a timeline estimate - free, with no obligation.
Yes. We prepare the full permit package including design review submission for 28-foot height limits, FAR caps, and neighborhood compatibility standards. We do not start work on permit-required construction without approved permits in hand. Call (669) 259-1843 to start the process.
Under Clause 1 of The Haven Standard, the price is written before anyone starts. The quote is flat, with a written scope and written warranty. No change proceeds without a signed change order. The documented photo record on every visit shows what was found and what was done, so there are no disputes about conditions. Since 2007, this discipline has kept our projects within a few percent of the agreed price. Call (669) 259-1843 for your written estimate.
Ready to add space to your Los Altos home? Call (669) 259-1843 to schedule your free estimate. Grant Rowan and our team will deliver a written price before any work starts, with every brand named, every scope item listed, and no change order without your signature.
Written by Grant Rowan, Owner at Rowan Construction Group, serving Los Altos since 2007.