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Mountain View · Attached ADU
One shared wall, a full second home on your Mountain View lot.
An attached ADU grows off your Mountain View house — its own door, kitchen and bath — built to read like the original home and engineered for the seismic ground under the valley floor.
Trusted by homeowners across Sacramento & surrounding areas.
Attached ADU in Mountain View — fast facts
City
Mountain View
ADU type
Attached ADU
Contractor license
CSLB #1119373
Free estimate
(916) 677-9774
Last updated
Joined, not freestanding
What an attached ADU really is
An attached ADU shares exactly one wall with your existing Mountain View house. That single wall is the entire line between this and a detached cottage in the back. Cross it, and the unit is a complete home — a private entrance off the side or rear, a working kitchen, a full bath, a bedroom a tenant reaches without walking through your living room. On lots this tight and this expensive, we lean toward attached. The new build ties into your roofline, your foundation and your wall line. On a flat-roof Eichler that tie-in is a design problem as much as a structural one, and getting it wrong is the kind of thing the neighbors notice. Done right, you can't find the seam from the curb.
Shares one wall; everything past it is fully independent
Private entrance, full kitchen, full bath, real bedroom
Ties into the existing roof, foundation and wall line
The wall between two homes
The shared-wall fire and sound assembly
Your shared wall changes character the moment two separate dwellings live on either side of it. Code wants it rated. Usually that's a one-hour fire assembly carried floor to roof — the correct gypsum layers, fireblocking at every penetration, and a sound-rated cavity so the Google engineer renting your unit isn't hearing your TV through the studs. This is the part owners don't see coming. Open the wall on a 1950s Old Mountain View bungalow and you may find old wiring and board sheathing that won't carry the rating as-is. An Eichler's post-and-beam wall is its own puzzle. So the existing side usually needs work too, not just the new build. We draw the assembly on the plans and build it to the listed spec.
One-hour rated separation between the two dwellings
Sound-rated cavity so neither household hears the other
Existing wall often needs upgrading to hit the rating
City of Mountain View permits
Permitting an attached ADU here
Your permit files with the City of Mountain View — its own counter, its own pace. Mountain View has leaned hard into housing, this being Google's hometown, and it's genuinely ADU-friendly. That doesn't make it fast. Fees run high and review takes its time. Attached units pull an extra look, because reviewers study how the addition meets your existing house, so your home's as-built condition matters more here than on a detached job. Design sensitivity is real on the Eichler tracts — a flat-roof, post-and-beam home does not forgive a mismatched addition, and the City knows it. State law keeps ADU review ministerial, so a complete set must be issued. But a thin submittal in Mountain View buys correction cycles you'll feel in weeks you didn't budget.
City of Mountain View review — ADU-friendly but not quick
Extra scrutiny on how the addition meets the existing house
High fees; a complete set keeps review ministerial
Shared utilities, real savings
Why the shared wall costs you less
The reason an attached ADU pencils cheaper than a detached one is sitting right in the name. You tap the foundation, the PG&E service and the water line already running to your house, instead of trenching the length of the lot to a freestanding cottage. That matters more here than almost anywhere — Bay Area detached units commonly land $400K to $750K and up, and the shared wall is how you cut a real piece off that. One honest caveat: at 750 sq ft the City can require a separate water meter, and PG&E may want a panel upgrade before a second all-electric kitchen's load lands. An attached unit also fits a tighter side yard than a detached one needs, which is most of the battle on a narrow Rex Manor or Whisman parcel.
Taps the existing foundation, PG&E service and water line
Cross the 750 sq ft line and a separate meter can apply
Fits a tighter side yard than a detached build needs
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Trusted by homeowners across Sacramento & surrounding areas.
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“Every ADU we build is designed to add long-term value and open new possibilities for your property. Let's build something great together.”
— Tim, ADU Specialist
Custom Designs
Built to fit your property & needs
Turnkey Process
We handle permits, plans & everything
Built to Last
Quality craftsmanship that stands the test
Financing Made Simple
$0 Down Options. Build Now, Pay Over Time.
You shouldn't have to drain your savings to build wealth. We partner with trusted ADU lenders to find financing that fits — many homeowners build with little to nothing out of pocket.
Home Equity (HELOC)
Tap your existing equity at competitive rates — the most popular way to fund an ADU.
Renovation Loans
Finance the build against your home's projected after-completion value.
ADU-Specific Financing
Specialized lenders who underwrite based on the rental income your ADU will produce.
Cash-Out Refinance
Roll the project into a new mortgage and keep one simple monthly payment.
Estimate Your Monthly Payment
See what financing your ADU could look like — and how rental income can help cover it.
$180,000Loan amount
Credit Score
Very good · 700–739
Estimated Monthly Payment
$1,320/mo
At 7.99% APR over 30 years (illustrative)
Often offset by $2,000–$3,500/mo in rental income
No prepayment penalties with most partners
Pre-qualification with no impact to your credit
Illustrative only — not a loan offer. Actual rates and terms are set by third-party lenders based on your qualifications.
Service areas
Where we build
Headquartered in the Greater Sacramento Area and serving homeowners from the Sierra foothills down through the Bay Area. Don't see your city? We probably still get there — just ask.
The most common things Sacramento homeowners ask before starting an ADU project.
An attached ADU shares one wall with your existing house. A detached unit stands free in the yard. That shared wall is the whole difference — it lets the new unit borrow your foundation, your PG&E service and your water line, which usually makes it cheaper than a freestanding cottage on the same Mountain View lot. In a market where detached units commonly run $400K to $750K and up, that gap isn't small. An attached unit also fits a narrower side yard, which matters on the tight parcels around Rex Manor, Whisman and the older blocks near Castro Street where there's no open ground to give up on all four sides.
With the City of Mountain View. The City handles ADU permits directly, and it's genuinely ADU-friendly — the town has pushed hard on housing. Honestly, friendly doesn't mean fast: fees are high and review takes its time. We handle the full submittal: site plan, floor plan, elevations, the structural tie-in and foundation details, Title-24, MEP, seismic design and PG&E coordination. State law keeps ADU review ministerial, so a complete, code-compliant set has to be issued. The game in Mountain View is turning in a clean, complete set so you're not stuck in correction cycles eating weeks you didn't plan for.
Yes. The Bay Area sits near several active faults, and Mountain View's valley-floor ground gets engineered for shaking like any other Bay structure. Your new unit gets shear walls, hold-downs and a foundation detailed for seismic demand, not a flat-inland copy. On an attached unit the tie-in to your existing house is where it counts most — the new structure has to move with the main home in a quake instead of tearing away from it at the shared wall. That junction is exactly where seismic detailing on an attached ADU earns its keep.
Once two separate dwellings sit on either side of a wall, code wants it rated — typically a one-hour fire assembly carried floor to roof, with the right gypsum layering and fireblocking. We also build a sound-rated cavity into it so your tenant isn't living inside your living room. On older Mountain View homes the existing wall usually needs upgrading to carry the rating — old wiring and board sheathing won't do it as-is — and on an Eichler the post-and-beam wall is its own detail. We catch all of that on the plans rather than mid-build.
That's the careful part, and I won't pretend it's trivial. Eichlers are flat-roof, post-and-beam, glass-heavy and very design-sensitive — a clumsy addition reads instantly. We match the roofline, the beam rhythm and the cladding so the new unit sits as part of the original architecture, not a lump bolted onto it. Tying a flat roof and a slab-on-grade Eichler into a new structure takes real detailing. The payoff of attached over detached here is that the match keeps the home's character intact, which is exactly what the City and your neighbors care about on those tracts.
At and above 750 square feet the City can require a separate water meter for the ADU instead of letting it ride on your existing service. Below that, you usually share. PG&E may also want a panel upgrade before you add a second all-electric kitchen's load. We size the unit knowing exactly where both lines sit, so you're not tripping a meter requirement to gain a handful of square feet you didn't actually need. With Mountain View's high fees, every avoidable trigger is worth dodging.
That's the honest question, and the answer is usually yes — because of the rents. Bay Area ADU construction is a different planet from Sacramento; detached units commonly land $400K to $750K and up. But tech-worker rental demand here is intense and steady, and rents run far above Sacramento. A quiet attached unit with its own entrance rents fast to someone walking or biking to a nearby campus. An attached build cuts cost by sharing your wall and utilities, and over the years you hold the property, the income often carries the unit and then some.
Straight answer: we're based in Sacramento, about 2.5 hours from Mountain View, and we extend down here for homeowners who want our craftsmanship and value, or for larger projects worth the drive. We're not pretending to be the corner outfit who's framed a hundred jobs on your block. What we bring is design-build discipline, real seismic and shared-wall experience, and Sacramento pricing sensibility applied to a market where local quotes can run wild. For the right project, that distance pays for itself.
Longer than Sacramento, and I won't dress that up. Mountain View's permitting is ADU-friendly on paper but not quick, and design review on a sensitive tract can add time. A clean, complete attached set keeps you out of correction loops, which is the single biggest schedule lever here. Construction depends on the tie-in and the seismic work. We give you a real schedule after we see the lot and how your house sits on it — not a generic number off a brochure.
That's the point of doing it right, and around here it's most of the job. We match the siding or stucco, carry the elevation lines across, and tie the new roofline into your existing roof so the addition reads as part of the original home. On a flat-roof Eichler or an older bungalow near Old Mountain View, that match is what keeps the City, the neighbors and the design reviewers satisfied. Someone walking past on the way to Castro Street shouldn't be able to find the seam between the old house and the new unit.
Other services
Not quite the right fit?
Every Sacramento ADU project is different. Here are the other paths we build under one roof — and we're happy to talk through which one fits your lot best.
We treat every home like it's our own — quality work, clear communication, and happy homeowners.
PaulOwner · Future Generation
9 min read2,021 words8 sections
Building an Attached ADU in Mountain View, Santa Clara County
An attached ADU in Mountain View borrows one wall from your existing house and turns the rest into a separate, legal home — its own entrance, kitchen and bath. We're a Sacramento design-build contractor, license #1119373, roughly 2.5 hours up the road. That distance is the first honest thing on this page: we extend down to Mountain View for owners who want our craftsmanship and value, or for projects big enough to earn the drive. What follows is how we think about attached units here, where Eichler design sensitivity and Bay Area economics change the math, and where it gets harder than the brochure says.
01Section
What "attached" actually buys you
The word attached holds the whole concept. Your new unit shares precisely one wall with your existing Mountain View house and is otherwise a complete, independent home — a private door off the side or rear, a real kitchen with its own range and sink, a full bath, and a bedroom a tenant reaches without setting foot in your space. That one shared wall is the only thing tethering the two homes. Everything else stands on its own.
That single connection is why owners pick attached over detached. You're not dropping a freestanding cottage at the back of a half-million-dollar lot and running utilities the length of the parcel to reach it. You grow off the house already standing. On a Mountain View lot, where land value is steep and parcels tend to be tight, pressing the new unit against the existing house sidesteps a chunk of the site's difficulty before you've poured a footing.
