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 Mountain View
Most Home Additions & ADU projects in Mountain View run $45,000-$130,000, and the cost moves most when we open a wall and find what a 1950s house has been hiding. If you live in Old Mountain View, Cuesta Park, or up near Moffett Field, you already know the housing stock: postwar single-family homes on slab or cripple-wall foundations, many with original electrical and framing that hasn’t seen a permit inspector since Eisenhower was president. We’re Barrett & Sons Construction, and we’ve spent 27 years working on exactly these houses. Tom Barrett and his sons run the crews, we pull every permit, and every price change lands in your hands as a written change order before a single stud gets touched. Call (877) 610-1318 for a free estimate on your Mountain View addition.
Why Barrett & Sons Construction Is Mountain View’s Preferred Home Additions & ADU Company
Homeowners in Mountain View have a particular reason to be careful about who they hire: this is a city where out-of-area contractors routinely stumble over rules that don’t exist twenty minutes south. The FAA Part 77 obstruction surfaces around Moffett Field impose real building-height ceilings and crane-permit requirements on projects in the northern ZIP codes, and a second-story addition in 94043 can need a Form 7460-1 airspace review before the city will even look at your permit. A contractor who doesn’t know that gets your project stopped cold. We know it, we file it, and we build it into the schedule from day one.
More than that, we’re a local name you can verify. Tom Barrett publishes his name, his address, and his license number. Our crew members carry the Barrett & Sons name, they’re background-checked, and they’re on-site most days. When you call (877) 610-1318, a live person answers. That matters in Mountain View, where the difference between a good addition and a year-long headache is usually whether the contractor picked up the phone when the inspector had a question.
Our Home Additions & ADU Services in Mountain View
Our Home Additions & ADU team handles everything from a 400-square-foot garage conversion to a full second-story addition. In Mountain View, the three most common requests we see are ADU design and permitting, second-story additions, and room additions, each with its own local wrinkles.
ADU Design & Permitting
Mountain View’s land values are among the highest in Santa Clara County, so an ADU is often the single smartest square-footage decision a homeowner can make. We handle the full design and permitting package, including the FAA Form 7460-1 submittal if your project is in the 94043 ZIP near Moffett Field. A typical ADU construction in Mountain View runs $90,000-$220,000, and the permitting path is where the schedule lives or dies. We submit drawings that anticipate the inspector’s concerns, not drawings that hope for the best.
Garage Conversion ADU
Garage conversions in Mountain View run $30,000-$80,000 and are extremely common in neighborhoods like Cuesta Park, where postwar garages sit on slabs that may or may not have adequate footings for habitable space. Opening the slab to install plumbing and electrical often triggers a foundation inspection, and if the original pour isn’t up to current code for an occupiable room, that’s exactly the kind of surprise that should have been an allowance on paper. We write it in from the start.
New Detached ADU
For Mountain View lots with the side or rear yard to spare, a new detached ADU at $90,000-$220,000 is the cleanest build. North Bayshore parcels on former bay mud need a geotechnical report before we can settle on a foundation design. Skip that report, and you’ll see settlement cracks and moisture wicking through the slab within the first year. We don’t skip it.
Junior ADU & Interior Conversion
A junior ADU, typically a bedroom plus kitchenette within the existing home footprint, is the fastest and least expensive path to a rentable or family unit in Mountain View. Attached conversion work runs from the lower end of our $45,000-$130,000 range. The work is lighter, but the code requirements are not: egress windows, fire separation, and sometimes a separate meter. We handle all of it, permits included.
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 Mountain View
When your Mountain View addition calls for hardscape, paving, or exterior finishes, we install brands you can look up: Techo-Bloc and Cambridge Pavers for paver driveways and patios, Quikrete for concrete work, Oldcastle for retaining systems. These aren’t mystery products from the back of a van. We specify them by name in your contract, line by line, so you know exactly what’s going in before we order it. If a material isn’t available locally, we tell you before you sign, not after we’ve torn into the wall.
Common Home Additions & ADU Problems We See in Mountain View Homes
- Undersized framing in 1950s and 1960s homes. Old Mountain View and Cuesta Park houses were built with 2x4s doing work that today’s code assigns to 2x6s or engineered beams. Opening a wall for an addition often means bringing the connected structure up to current load standards, which is a code requirement, not an upsell.
- Knob-and-tube and spliced Romex. We regularly find original knob-and-tube wiring that someone spliced into modern Romex without a junction box. It’s a fire hazard, and once a permit is pulled, the inspector is going to require it gone. We build an electrical allowance into every Mountain View addition scope.
- Cripple-wall foundations needing seismic retrofit. Many postwar Mountain View homes sit on cripple-wall foundations. California Building Code requires seismic retrofitting when significant remodeling permits are pulled. That’s a cost no one likes, but it’s a cost you should see coming in writing.
- Bay mud and high groundwater in North Bayshore and Shoreline. The land near Google’s campus and the Shoreline District is former tideland. Building there without a geotechnical report is how you get a cracked slab and water in the crawlspace. We order the report before we draw final plans.
Pricing for Home Additions & ADU in Mountain View, CA
| Project Type | Mountain View Price Range |
|---|---|
| Home Addition | $45,000-$130,000 |
| ADU Construction | $90,000-$220,000 |
| Garage Conversion | $30,000-$80,000 |
What drives the spread? Foundation condition, the FAA airspace review if you’re in 94043 near Moffett Field, and how much of the original electrical and framing has to come out once we open the walls. In Old Mountain View, a second-story addition almost always includes a seismic retrofit line item. In North Bayshore, it includes a geotechnical report. We put all of that in writing before we start, and if something does change mid-project, you get a written change order before we proceed. Call (877) 610-1318 for a free estimate on your specific house.
We Also Serve Cities Near Mountain View
Barrett & Sons Construction serves Mountain View and the surrounding communities, including Los Altos, Los Altos Hills, Sunnyvale, and Stanford. If you’re in one of those cities and planning a Home Addition or ADU, the same local crew, written change orders, and 90-Day Done Right Promise apply. Call (877) 610-1318 and ask for a free estimate.
Serving Mountain View, CA - Our Local Coverage Area
We’re based in the Mountain View 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 Mountain View
Do I need an FAA airspace review for a second-story addition in the 94043 ZIP near Moffett Field?
Yes, in most cases. Any structure or crane that exceeds the imaginary FAA Part 77 obstruction surface around Moffett Federal Airfield requires a Form 7460-1 Notice of Proposed Construction and a “no hazard” determination before the city will issue a building permit. This applies to second-story additions, tall ADUs, and even crane staging. We file this for you. Call (877) 610-1318 if you’re not sure whether your project triggers it, and we’ll check your parcel.
What code upgrades trigger the minute I open the walls on a 1950s Mountain View home?
The most common are electrical, structural, and seismic. Original knob-and-tube wiring must come out, undersized framing must be brought to current load standards, and a cripple-wall foundation will trigger a mandatory seismic retrofit under California Building Code. These are not optional once a permit is pulled. We write allowances for each into your contract so the cost doesn’t ambush you at week four. Call (877) 610-1318 for a detailed scope review.
Will my Cuesta Park garage conversion require a foundation upgrade?
Quite possibly. Cuesta Park garages from the 1950s and 1960s were poured as unheated, non-habitable slabs. Converting one to an ADU means cutting the slab for plumbing and electrical, which exposes the footing to an inspector who will judge it against current habitable-space standards. If the footing is undersized, you’ll need an upgrade. We include a foundation allowance in every Cuesta Park garage conversion quote. Call (877) 610-1318 for a free on-site look at your slab.
Why are ADU additions the most common residential project in Mountain View?
Because Mountain View land values are among the highest in Santa Clara County, and an ADU extracts rentable or family square footage from land you already own. For half the cost of trading up to a bigger house, you can add a rentable unit that pays for itself. A garage conversion ADU in Mountain View runs $30,000-$80,000; a new detached ADU runs $90,000-$220,000. Call (877) 610-1318 and we’ll run the numbers on your specific lot.
How do you keep a Home Addition in Old Mountain View on the original draw schedule when you find damaged framing?
We write allowances into the contract for structural, electrical, and seismic upgrades before we open the first wall. Here’s what that looks like in practice. On a second-story addition in Old Mountain View, our crew opened original 1950s walls to find undersized 2×4 framing and knob-and-tube wiring spliced into modern Romex without a junction box. Because we had written allowances for electrical and structural upgrades in the scope of work, we installed new load-bearing beams, replaced the subfloor, and brought the rough-in to current code, then walked the city inspector through the open walls for an inspection sign-off before drywall. The job stayed on schedule because the allowance was already on paper. That’s how we run every Mountain View project. Call (877) 610-1318 to get your allowance structure in writing.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Mountain View and the surrounding Bay Area since 1998.