Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
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AfterFast, Reliable Home Additions & ADU Across Los Altos Hills
If you own property in Los Altos Hills, you already know the two conversations every neighbor has had: how long it takes to get a permit through the Town, and how few Los Altos Hills Roofing and construction contractors actually understand the 1-acre lot rules, the fire-safety codes, and the septic setbacks before they put a drawing in front of you. We do. Home additions and ADUs here are not the same as one town north or one town south. Our Home Additions & ADU team has walked enough hillside parcels between Page Mill Road and Moody Road to know what the Building Department will flag before the first submission. Call (877) 610-1318 and we’ll come walk your property with you.
Why Barrett & Sons Construction Is Los Altos Hills’s Preferred Home Additions & ADU Company
We’re an owner-operated company, not a dispatch board. Tom Barrett started this firm in 1998, and his sons are on job sites in Los Altos Hills most days. If you call the office, a live person answers, 24/7. If you want to see who you’re hiring, look up Tom’s name, address, and license number. They’re published, verifiable, and have been for close to three decades. That matters in a town where a lot of property owners have been burned before by a bid that didn’t survive the first change order.
We hold a strong local reputation in Los Altos Hills because we don’t treat this town like an afterthought, whether we’re handling a full addition or Windows & Doors - Los Altos Hills upgrades. We know that a second-story addition off Altamont Road means a geotech report before the architect gets too far. We know that a garage conversion on a steep lot near Natoma Road can trigger drainage review. And we know the Town’s lot-coverage caps better than any out-of-area company ever will. You’ll get a written scope, written allowances, and written change orders before anything changes. Every permit gets pulled, and every inspection gets signed. That’s not a selling point for us. That’s the job.
Our Home Additions & ADU Services in Los Altos Hills
ADU Design & Permitting
The biggest advantage we bring to an ADU in Los Altos Hills is that we think about the Town’s rules before you pay for plans you can’t build. Lot-coverage limits, impervious-surface caps, and fire-hazard zone requirements all shape what’s actually possible on your parcel. We handle the design conversation early, coordinate with your architect or ours, and submit a package that has a realistic chance of passing on the first review. A permitted ADU in Los Altos Hills typically runs $90,000 to $220,000 depending on whether it’s attached, detached, or a conversion.
Garage Conversion ADU
Converting an existing garage is often the most cost-effective ADU path in Los Altos Hills, usually landing between $30,000 and $80,000. But it’s not a simple drywall job. Many garages in town sit on slabs that predate current seismic standards, and the Town will ask about insulation, egress, and fire-rated separation from the main house. We’ve done enough of these to know exactly what the inspector will look for, and we price it honestly from the start.
New Detached ADU
A detached ADU on a Los Altos Hills hillside is a small custom home, not a shed with a bathroom. Expect to budget $90,000 to $220,000, with the final number driven by foundation work, grading, and the fire-resistant materials the CAL FIRE standards require. We’ve built detached units on parcels where equipment access meant hand-carried materials down a winding private driveway. It can be done, but you want a crew that’s done it before, not one learning on your property.
Junior ADU & Interior Conversion
A junior ADU, typically carved from existing interior space, is often the fastest way to add a rental unit or a space for an aging parent without triggering the full detached-ADU permitting path. Los Altos Hills allows JADUs under state law, but the Town’s septic constraints can shape whether a separate bathroom is feasible. We’ll tell you the truth about what your parcel will and won’t support, in writing, before you commit. We also handle Kitchen Remodeling in Los Altos Hills and Bathroom Remodeling in Los Altos Hills when a larger home addition includes either space.
Room additions, second-story additions, and sunrooms round out the services our Home Additions & ADU crew handles. In Los Altos Hills, a typical room addition runs $45,000 to $130,000, and a full second story can push that higher once structural and fire-safety upgrades are factored in.
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 Hills
When we quote materials on a Los Altos Hills job, we quote brands you can look up before you sign. On hardscape-adjacent additions, that means Belgard and Techo-Bloc. For the structure itself, we frame and finish with materials selected for fire resistance, not just cost. We don’t install mystery brands off a van, and we don’t swap an allowance for a cheaper substitute without a written change order. If the brand matters to you, it’s in the contract. If it’s not in the contract, it’s a conversation before it becomes a purchase.
Common Home Additions & ADU Problems We See in Los Altos Hills Homes
- Lot-coverage surprises. Because the Town ties impervious-surface caps to parcel size, a homeowner who wants a 700-square-foot ADU can discover their existing motor court already eats the allowance. We audit existing hardscape before design so you don’t pay for plans that get rejected.
- Septic and setback conflicts. Nearly all of Los Altos Hills runs on private septic rather than municipal sewer. When an addition or ADU expands your building footprint, the septic leach field and its required setbacks have to be re-verified. We bring septic engineering in early, not after demolition.
- Fire-hazard zone requirements. Much of Los Altos Hills sits in a Very High Fire Hazard Severity Zone, so additions must meet ember-resistant construction standards. That means Class A roofing material, ember-resistant vents, and fire-rated cladding choices that a flat-land remodel in Mountain View would never trigger.
- Expansive clay and slope movement. The same foothill soils that make the views possible also make foundations move. We regularly see hairline cracks and settling on older mid-century ranch homes, and we order geotech reports as a standard part of the permit package here, not as an upsell.
Pricing for Home Additions & ADU in Los Altos Hills, CA
In Los Altos Hills, a home addition typically lands between $45,000 and $130,000. A full ADU runs $90,000 to $220,000, while a garage conversion sits at $30,000 to $80,000. What moves the number is not mystery markup. It’s grading, foundation work, fire-resistant materials, septic engineering, and the Town’s permit review timeline. We give free estimates, and every estimate is a written line-item document, not a verbal range you can’t hold us to. No trip charge inside the county, and if you have another written bid, we’ll give you a free second opinion. Call (877) 610-1318. The estimate costs you nothing, and you’ll know the real number before you sign.
We Also Serve Cities Near Los Altos Hills
Beyond Los Altos Hills, our crews handle additions and ADUs in Los Altos, Mountain View, Stanford, and Palo Alto. The permitting rules change at every city line, and we’ve got working knowledge of all of them. Dispatch coordinates from our San Francisco Bay Area office, with local crews serving Los Altos Hills directly.
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
We respond to Los Altos Hills service requests quickly, typically scheduling an on-site visit within a few days, depending on how full the schedule is. Because our crews serve Los Altos Hills regularly, we aren’t an out-of-area company guessing at drive times. For a true emergency related to structural safety, call (877) 610-1318 and a live person will answer, 24/7.
Yes. We work all over Los Altos Hills, including parcels off Page Mill Road, Moody Road, Natoma Road, and Altamont Road, throughout the 94022 ZIP code. The permitting office treats every parcel a little differently, and we’re familiar enough with the town’s development standards to know what questions to ask before you spend money on design.
In Los Altos Hills, expect $45,000 to $130,000 for a room addition, where the same scope in Mountain View or Palo Alto might land slightly lower because there’s no 1-acre lot coverage review or hillside grading to content with. Los Altos Hills adds real permitting, geotech, and fire-safety costs that flatland cities don’t. We’ll show you exactly where the money goes on your estimate. Call (877) 610-1318 for a free, line-item quote.
Only if the scope changes, and only after you sign a written change order. That’s our rule, and it’s the whole reason we survive in a town full of people who have been surprised by final bills before. No allowance gets spent without a number on paper. No change happens without your signature. The 90-Day Done Right Promise is written into every contract we sign in Los Altos Hills.
Yes. Every eligible job gets a permit, and every required inspection gets signed. In Los Altos Hills, given the fire-hazard-zone rules and septic setbacks, pulling permits isn’t optional it’s the only way the structure is legal and insurable. If a contractor tells you to skip it, walk away. Call (877) 610-1318 and we’ll show you what a compliant permit package looks like.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Los Altos Hills and the surrounding Bay Area since 1998. Phone: (877) 610-1318.