How Much Does an ADU Cost in Mountain View? (2026)
Mountain View ADUs cost $125,000-$475,000+ in 2026 depending on type and scope. Garage conversions start at $125K. Attached ADUs run $165K-$310K. Detached ADUs cost $275K-$475K+. Mountain View's proximity to Google, compact lot sizes, and large Eichler housing stock create unique ADU considerations. The city's efficient permitting process and strong rental demand make ADU construction a solid investment.
How much does an ADU cost in Mountain View?
ADU costs in Mountain View range from $125,000 for a garage conversion to $475,000+ for a large detached unit in 2026. The average detached ADU costs $275K-$425K. Attached ADUs average $165K-$310K. Mountain View's permitting runs 8-12 weeks, and rental demand near Google supports rents of $2,500-$3,800/month for well-finished units.
ADU Costs in Mountain View: What to Expect in 2026
Mountain View is at the center of Silicon Valley’s tech economy. With Google’s global headquarters and a growing roster of tech employers, the city generates enormous housing demand. Mountain View’s median home price sits near $2 million, and rental rates remain among the highest in the Bay Area. For homeowners, an ADU represents both a smart financial investment and a practical way to house family members in one of the country’s most expensive real estate markets.
This guide covers 2026 ADU costs specific to Mountain View: what each type costs to build, permit fees and regulations, what factors drive costs up or down, and how to plan your budget.
All pricing is approximate, reflects 2026 Bay Area market conditions, and is subject to change. Every project is unique. Final costs are determined on a project-by-project basis during our design phase.
For Bay Area-wide ADU pricing, see our ADU cost guide.
Cost by ADU Type
The type of ADU you build is the largest cost variable. Here is what Mountain View homeowners are paying in 2026:
| ADU Type | Cost Range | Cost/Sqft | Timeline | Typical Size |
|---|---|---|---|---|
| Garage Conversion | $125,000-$160,000 | $165-$365 | 4-6 months | 400-500 sqft |
| Attached ADU | $165,000-$310,000 | $310-$460 | 6-10 months | 400-800 sqft |
| Detached ADU | $275,000-$475,000+ | $365-$510 | 8-14 months | 500-1,200 sqft |
| Junior ADU (JADU) | $85,000-$155,000 | $210-$365 | 3-5 months | 200-500 sqft |
These ranges represent construction costs. Permits, design, and utility connections add to these totals.
Garage Conversions
Many Mountain View homes have attached two-car garages that convert well into ADU space. The existing structure eliminates foundation, framing, and roofing costs. The core investment covers insulation, drywall, flooring, kitchen and bathroom installation, plumbing, electrical, and HVAC.
A one-car garage conversion (250-400 sqft) runs $85,000-$125,000. A two-car garage (400-600 sqft) costs $125,000-$160,000. Mountain View’s parking-exempt ADU rules mean you do not need to replace the lost garage parking.
Attached ADUs
Attached ADUs connect to the main home and share at least one wall. In Mountain View, where many lots are 5,000-7,000 sqft, attached ADUs are a practical choice when setbacks leave limited space for a detached structure. Utility connections are simpler and less expensive than detached alternatives.
Expect to pay $165,000-$310,000 for an attached ADU. The range reflects size (400-800 sqft), structural integration complexity, and finish selections.
Detached ADUs
Detached ADUs offer maximum privacy and the highest rental potential. In Mountain View, a detached ADU costs $275,000-$475,000+. These standalone structures require new foundations, full framing, roofing, and independent utility connections.
Mountain View’s compact lots mean detached ADU footprints are often constrained by the 4-foot side and rear setbacks. On a typical 6,000 sqft lot, the practical maximum detached ADU size may be 600-800 sqft after setback calculations.
Junior ADUs (JADUs)
JADUs convert existing space within your home into a separate living unit (up to 500 sqft). They require a kitchenette and a separate entrance. At $85,000-$155,000, JADUs are the lowest-cost entry point for adding a rental unit or family suite.
Mountain View ADU Permit Fees and Soft Costs
| Cost Category | Typical Range | Notes |
|---|---|---|
| Building permit fees | $3,500-$16,000 | Based on project scope and valuation |
| Architectural/design fees | $9,000-$25,000 | Plans, engineering, Title 24 compliance |
| Utility connections | $5,000-$16,000 | Water, sewer, electrical; detached costs more |
| Impact fees (750+ sqft) | $5,000-$12,000 | Schools and parks for units over 750 sqft |
| Impact fees (under 750 sqft) | $0 | Waived under California law |
| Survey and soils report | $2,000-$5,000 | Required for new detached structures |
| Landscaping and site restoration | $3,000-$10,000 | Yard restoration, fencing, hardscape |
Total soft costs typically add $22,000-$60,000 on top of construction.
What Drives ADU Costs in Mountain View
Compact Lot Sizes
Mountain View’s typical residential lots (5,000-7,000 sqft) are among the smallest in the South Bay. After accounting for the primary home, setbacks, and required open space, the buildable area for a detached ADU is often limited. Tight sites increase construction costs because:
- Equipment access may be restricted, requiring more manual labor
- Material staging areas are limited, increasing delivery frequency
- Crane or pump truck access may require temporary street use permits
Eichler Home Compatibility
Mountain View has one of the Bay Area’s largest concentrations of Eichler homes, particularly in Monta Loma and Old Mountain View. Building an ADU on an Eichler lot involves:
- Working around the home’s distinctive post-and-beam construction
- Respecting the relationship between the Eichler’s atriums and courtyards and the new structure
- Tying into radiant floor heating systems (if extending attached ADUs)
- Addressing carport-to-ADU conversions (Eichlers often have carports instead of garages)
Eichler lot ADU projects typically add 5-15% in cost due to these considerations.
Utility Infrastructure
Many Mountain View homes were built in the 1950s and 1960s with 100-amp electrical service. ADU construction requires a separate electrical panel (California law), and older homes often need a main panel upgrade to 200-amp service ($3,000-$6,000) before the ADU panel can be installed.
Detached ADUs require trenching for water, sewer, and electrical lines from the main house or street connection. In Mountain View, where yards are compact, the trenching distance is typically shorter (20-50 feet), keeping connection costs at $8,000-$16,000.
Finish Level
Mountain View’s market supports a range of finish levels. For rental ADUs, mid-range finishes deliver the best return:
| Finish Level | Description | Added Cost vs. Standard |
|---|---|---|
| Standard | Laminate countertops, vinyl flooring, builder-grade fixtures | Baseline |
| Mid-range | Quartz countertops, LVP flooring, upgraded fixtures | +$15,000-$28,000 |
| High-end | Stone countertops, hardwood flooring, custom cabinetry | +$35,000-$70,000+ |
Mountain View ADU Regulations
- Lot zoning: ADUs are permitted on residential lots with an existing single-family home
- Maximum size: Detached ADUs up to 1,200 sqft. Attached up to 50% of primary home, max 1,200 sqft
- Setbacks: 4 feet from side and rear property lines for detached ADUs
- Height: Up to 16 feet (single-story) or 18 feet per state allowances
- Parking: No additional parking required
- One ADU plus one JADU per single-family lot
- Rent stabilization: Mountain View’s CSFRA (rent stabilization) applies to multi-family units built before 1995. New ADUs are generally exempt, but verify with the city’s Rental Housing Committee
Mountain View’s Community Development Department processes ADU applications and has published guidelines specific to local lot configurations.
How Mountain View Compares to Other Bay Area Cities
| City | Estimated Cost (600 sqft Detached) | Permit Timeline | Key Difference |
|---|---|---|---|
| Mountain View | $275,000-$385,000 | 8-12 weeks | Compact lots, Eichler considerations |
| San Jose | $250,000-$350,000 | 6-10 weeks | Lower costs, ADU Ally program |
| Sunnyvale | $270,000-$380,000 | 8-12 weeks | Very similar market and process |
| Cupertino | $290,000-$400,000 | 8-12 weeks | Higher finish expectations, Apple effect |
| Palo Alto | $320,000-$450,000 | 10-16 weeks | Premium market, longer review times |
Mountain View costs are moderate for the area, sitting between the value-oriented San Jose market and the premium Cupertino and Palo Alto markets.
Sample ADU Budgets for Mountain View
Budget Example: 450 sqft Garage Conversion
| Line Item | Cost |
|---|---|
| Construction | $118,000 |
| Building permits | $4,500 |
| Design and engineering | $9,000 |
| Utility upgrades | $5,500 |
| Landscaping/site restoration | $3,500 |
| Total | $140,500 |
Budget Example: 700 sqft Detached ADU
| Line Item | Cost |
|---|---|
| Construction | $290,000 |
| Building permits | $10,000 |
| Design and engineering | $18,000 |
| Utility connections | $12,000 |
| Survey and soils report | $3,500 |
| Landscaping/site restoration | $6,000 |
| Total | $339,500 |
These are mid-range estimates. Your final cost depends on lot conditions, finish selections, and site access.
How to Control Your Mountain View ADU Budget
Right-Size for Your Lot
On Mountain View’s compact lots, a 600-700 sqft ADU is often the sweet spot between livability and cost efficiency. Staying under 750 sqft eliminates impact fees ($5,000-$12,000 savings) without sacrificing much in rental income. A well-designed 700 sqft unit with a separate bedroom commands nearly the same rent as a 900 sqft unit.
Consider a Garage Conversion
If your property has a two-car garage, converting it to an ADU saves $100,000-$200,000 compared to a detached build. The structure, foundation, and roof already exist. Mountain View does not require replacement parking, so you lose the garage space without a regulatory penalty.
Design for Efficiency
Smart floor plans maximize every square foot. A combined living-kitchen area, a well-placed bathroom, and a functional bedroom can fit comfortably in 500-600 sqft. Skip hallways and wasted transition spaces. Your architect should prioritize livability over raw square footage.
Lock in Your Budget Before Building
At Custom Home, our Phase 1 design process finalizes every detail, from cabinet hardware to light fixture placement, before we provide a locked-in construction price. You know the total cost before any work begins. This eliminates the change orders that push most ADU projects 10-20% over their original budgets.
Why Mountain View Homeowners Choose Custom Home
Custom Home Design and Build has been building ADUs across Mountain View since 2005. Based in nearby San Jose, we understand the city’s lot configurations, Eichler compatibility requirements, permitting process, and rental market.
Our ADU process:
- Free consultation. We assess your lot, discuss your goals, and provide a realistic budget range.
- Phase 1: Design. Full architectural plans, 3D renderings, material selections, and a locked-in construction price.
- Phase 2: Build. Permitted construction with weekly progress updates and a dedicated project manager.
Start Your Mountain View ADU Project
Mountain View’s strong rental demand, proximity to major tech employers, and California’s ADU-friendly laws make it an excellent city for an ADU investment. Whether you are converting a garage, building a detached unit, or creating a JADU for a family member, the key is starting with accurate numbers and a clear plan.
Ready to explore what an ADU would cost on your specific Mountain View property? Contact Custom Home for a free consultation. We will visit your site, evaluate your lot, and give you a realistic budget based on your property, your goals, and your neighborhood.
Frequently Asked Questions
What is the maximum ADU size allowed in Mountain View?
Mountain View follows California state ADU law. Detached ADUs can be up to 1,200 sqft on properties with a single-family home. Attached ADUs can be up to 50% of the primary home floor area, with a maximum of 1,200 sqft. JADUs are capped at 500 sqft within the existing home footprint. Mountain View's typically compact lots (5,000-7,000 sqft) mean setback calculations, not size caps, often determine the practical maximum.
Can I build an ADU on an Eichler property in Mountain View?
Yes. Eichler homes are among the most common properties in Mountain View, and ADUs can be built on these lots. However, Eichler lots are often compact (6,000-7,500 sqft), which limits detached ADU footprints after setbacks. Attached ADUs or garage conversions may be more practical. The ADU's design does not need to match the Eichler aesthetic, but many homeowners choose mid-century compatible styling for visual cohesion.
How long does it take to build an ADU in Mountain View?
Mountain View ADU permits typically take 8-12 weeks for approval. Total project timelines run 4-6 months for garage conversions, 6-10 months for attached ADUs, and 8-14 months for detached ADUs. These timelines include design, permitting, and construction. Mountain View's electronic plan review system helps expedite the permit process.
What rent can I charge for an ADU in Mountain View?
Mountain View ADU rental rates range from $2,000-$3,800+ per month in 2026, depending on size, finishes, and location within the city. Studio and one-bedroom ADUs (400-600 sqft) rent for $2,000-$2,800/month. Larger one- or two-bedroom units (700-1,200 sqft) command $2,800-$3,800/month. Note that Mountain View has a rent stabilization ordinance (CSFRA) that applies to properties built before 1995, but new ADUs are generally exempt.