Complete Guide to Building an ADU in Mountain View
Mountain View's position at the center of Silicon Valley, anchored by Google's headquarters, creates strong demand for housing and rental units. Building an ADU in Mountain View costs $250,000-$500,000+ in 2026. The city follows California state ADU law with ministerial approval, 4-foot side and rear setbacks, and no parking requirements. Many Mountain View properties qualify for the 18-foot height allowance due to proximity to VTA light rail and Caltrain stations, opening up two-story ADU designs. This guide covers Mountain View's ADU regulations, lot types, costs, popular designs, permit process, and how Custom Home Design and Build handles ADU projects.
What are the ADU regulations in Mountain View?
Mountain View follows California state ADU law. Detached ADUs can be up to 1,200 sqft. Setbacks are 4 feet on sides and rear for new construction. ADUs are approved ministerially. No additional parking is required. Many properties qualify for 18-foot height limits due to transit proximity, allowing two-story designs.
Why Mountain View Is a Prime Location for ADUs
Mountain View sits at the intersection of Silicon Valley’s strongest market forces: massive tech employment (led by Google’s Googleplex), limited housing supply, and rental demand that keeps vacancy rates low and rents high. A one-bedroom rental unit in Mountain View commands $2,500 to $3,500 per month in 2026, making an ADU one of the highest-returning home improvements a property owner can make.
Beyond rental income, ADUs in Mountain View serve growing families. Aging parents who want to live nearby, adult children saving for their own home, and homeowners who need a dedicated home office or studio all benefit from a well-designed ADU on the property.
Mountain View’s ADU environment is particularly favorable. The city follows California state law with ministerial approval, meaning your ADU is reviewed against objective standards rather than subjective design judgments. Many properties qualify for taller height limits due to proximity to transit, opening up two-story designs that make the most of smaller lots.
Mountain View ADU Regulations
Size Limits
| ADU Type | Maximum Size |
|---|---|
| Detached ADU | Up to 1,200 sqft |
| Attached ADU | 50% of primary home or 1,200 sqft (whichever is less) |
| Junior ADU (JADU) | Up to 500 sqft (within the existing home) |
State-mandated minimums ensure you can build at least 850 sqft for a studio or one-bedroom and 1,000 sqft for a two-bedroom unit, regardless of the 50% calculation for attached units.
Setback Requirements
- 4-foot side and rear setbacks for new detached and attached ADUs
- Front yard setback per the underlying zoning district
- No setback adjustments required for conversions of existing structures
If your existing garage sits 2 feet from the rear property line, you can convert it to an ADU without moving it back to 4 feet. The setback waiver for existing structures is one of the most valuable provisions for garage conversions.
Height Limits
Mountain View’s transit-rich environment gives many homeowners access to taller ADU height limits:
- 16 feet for standard detached ADUs
- 18 feet if within half a mile of a major transit stop (VTA light rail, Caltrain)
- Taller allowances possible if the ADU roof pitch matches the primary home
Mountain View has multiple transit stops that qualify: the Mountain View Caltrain/VTA station, the Middlefield VTA light rail station, and the Whisman VTA station. Properties within half a mile of these stations can build 18-foot ADUs, which comfortably accommodates two-story designs.
Parking
No additional parking is required for any ADU in Mountain View. Convert your garage, build in your driveway, or place a detached unit in your backyard. The parking waiver applies citywide.
Units Allowed
On a single-family lot:
- One ADU (detached or attached) plus one JADU
Lot Types and ADU Feasibility in Mountain View
Standard Lots (5,000-7,000 sqft)
The majority of Mountain View’s residential lots fall in this range. These lots can accommodate a detached ADU of 500-800 sqft in the rear yard, depending on where the primary home sits and how much setback space is available. Garage conversions are ideal for lots where the backyard is tight.
Mid-Size Lots (7,000-10,000 sqft)
Properties in neighborhoods like Old Mountain View and parts of Monta Loma have larger lots that provide more flexibility. A full 1,000-1,200 sqft detached ADU is feasible on these lots while preserving usable outdoor space.
Corner Lots
Corner properties offer the advantage of two street frontages, making it possible to give the ADU its own address and separate entrance. This improves privacy for both the main home and the ADU occupant.
Eichler Lots
Mountain View’s Eichler neighborhoods present unique ADU opportunities. The flat roof aesthetic of these homes pairs well with modern ADU designs, and many Eichler lots have spacious rear yards suited for detached units.
ADU Costs in Mountain View
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.
| ADU Type | Typical Size | Cost Range | Timeline |
|---|---|---|---|
| Garage Conversion | 400-500 sqft | $100,000-$180,000 | 6-10 months |
| Small Detached ADU | 400-600 sqft | $180,000-$280,000 | 10-14 months |
| Mid-Size Detached ADU | 600-900 sqft | $280,000-$380,000 | 10-16 months |
| Full-Size Detached ADU | 900-1,200 sqft | $380,000-$500,000+ | 12-18 months |
| Attached ADU | 400-800 sqft | $180,000-$320,000 | 8-14 months |
| Junior ADU (JADU) | Up to 500 sqft | $75,000-$140,000 | 4-8 months |
Key Cost Drivers
- Utility extensions. Running water, sewer, gas, and electrical to a detached ADU involves trenching and connection fees. Budget $15,000-$35,000 for utility work on a detached unit.
- Foundation. Slab-on-grade is the most cost-effective option. Raised foundations or pier-and-beam on uneven terrain cost more.
- Two-story construction. While two-story ADUs maximize space on smaller lots, they cost more per square foot than single-story designs due to structural requirements and staircase construction.
- Kitchen and bath. These rooms drive a disproportionate share of ADU costs. A full kitchen with quality appliances costs $20,000-$45,000. Each bathroom runs $15,000-$30,000.
- Exterior compatibility. Matching the ADU’s exterior to the primary home (siding, roofing, paint) creates a cohesive property appearance and supports property value.
Sample Budget: 650 Sqft Detached ADU
A representative budget for a one-bedroom detached ADU on a standard Mountain View lot:
| Budget Category | Estimated Cost |
|---|---|
| Architecture and engineering | $15,000-$25,000 |
| Permits and fees | $10,000-$20,000 |
| Site preparation | $6,000-$12,000 |
| Foundation (slab on grade) | $16,000-$26,000 |
| Framing and structural | $35,000-$52,000 |
| Roofing | $8,000-$14,000 |
| Electrical (including panel upgrade) | $15,000-$24,000 |
| Plumbing | $12,000-$22,000 |
| HVAC (mini-split) | $7,000-$12,000 |
| Insulation and drywall | $12,000-$18,000 |
| Flooring | $8,000-$14,000 |
| Kitchen (complete) | $22,000-$40,000 |
| Bathroom | $15,000-$25,000 |
| Windows and doors | $8,000-$14,000 |
| Exterior finish | $10,000-$18,000 |
| Utility connections | $18,000-$32,000 |
| Landscaping | $4,000-$8,000 |
| Total estimated range | $221,000-$376,000 |
Permit Process in Mountain View
Mountain View processes ADU applications ministerially through the Community Development Department. The process is straightforward for well-prepared submittals.
Steps
- Design and engineering. Create architectural plans, structural engineering, and Title 24 energy compliance documents.
- Application submittal. Submit to the Community Development Department with required fees.
- Plan review. Staff checks for code compliance. State law mandates 60-day processing for complete applications.
- Corrections (if needed). Any plan corrections are addressed and resubmitted.
- Permit issuance. Pay fees and receive your building permit.
- Construction with inspections. Build the ADU with city inspections at foundation, framing, rough mechanical, insulation, and final stages.
- Certificate of occupancy. Final inspection approves the ADU for habitation.
Timeline
| Phase | Duration |
|---|---|
| Design and engineering | 4-8 weeks |
| Permit review | 4-8 weeks |
| Construction | 4-8 months |
| Total | 10-16 months |
Popular ADU Designs for Mountain View
Modern Studio (450-550 sqft)
An efficient open-concept layout with a combined living-kitchen area, a sleeping alcove or small bedroom, and a full bathroom. Ideal for single occupants or couples. Monthly rental potential: $2,200-$2,800.
One-Bedroom with Outdoor Connection (600-750 sqft)
A bedroom, living area, full kitchen, and bathroom with a covered patio or deck that extends the living space outdoors. Mountain View’s mild climate makes outdoor living spaces practical year-round. Monthly rental potential: $2,500-$3,200.
Two-Bedroom Family Unit (850-1,100 sqft)
Two bedrooms, one or two bathrooms, a full kitchen, and a living area. This layout serves families, aging parents, or roommates. The two-bedroom configuration commands the highest rental premiums. Monthly rental potential: $3,200-$4,000.
Garage Conversion Studio (400-500 sqft)
Converting an existing garage into a studio apartment is the fastest and most affordable ADU path. The existing walls and roof provide a shell, and the conversion adds insulation, finished flooring, plumbing, kitchen, bathroom, windows, and a separate entrance. Monthly rental potential: $2,000-$2,600.
Rental Income Potential
Mountain View’s rental market is one of the strongest in the Bay Area. Here is what ADU owners can expect:
| ADU Size | Bedrooms | Monthly Rent Range | Annual Gross Income |
|---|---|---|---|
| 450-550 sqft | Studio | $2,200-$2,800 | $26,400-$33,600 |
| 600-750 sqft | 1 BR | $2,500-$3,200 | $30,000-$38,400 |
| 850-1,100 sqft | 2 BR | $3,200-$4,000 | $38,400-$48,000 |
These rental rates reflect 2026 market conditions near Google and other Mountain View tech employers. Actual rents depend on location within the city, finish quality, amenities, and market conditions at the time of listing.
Why Custom Home Design and Build
Custom Home Design and Build has been constructing ADUs across the Bay Area since 2005. Our Mountain View projects benefit from our understanding of the city’s lot conditions, transit proximity rules, and the design expectations of homeowners in this tech-centered market.
Our design-build process covers everything:
- Architectural design optimized for your lot
- Structural engineering for foundation and framing
- Permit application and city coordination
- Full construction with licensed crews
- Project management from design through final inspection
One team, one contract, and a locked-in price before construction begins.
Start Your Mountain View ADU
Whether you are looking to generate rental income near Google, create a home for family members, or add long-term value to your property, an ADU is one of the smartest investments you can make in Mountain View.
Contact Custom Home Design and Build for a free ADU consultation. We will evaluate your lot, discuss design options, and walk you through the permit process. Call (888) 306-1688 or complete our contact form to schedule your consultation.
Frequently Asked Questions
How much does it cost to build an ADU in Mountain View?
ADU construction in Mountain View costs $250,000-$500,000+ in 2026. Garage conversions start around $100,000-$180,000. A 600 sqft detached ADU typically runs $230,000-$330,000. A full 1,200 sqft detached ADU costs $380,000-$500,000+. Site conditions, utility connections, and finish level are the primary cost variables.
Can I build a two-story ADU in Mountain View?
Yes, in many cases. Properties within half a mile of a major transit stop (including VTA light rail stations and Caltrain) qualify for an 18-foot ADU height limit. An even taller allowance may apply if the ADU's roof pitch matches the primary home. Two-story designs under 18 feet are feasible and popular in Mountain View's transit-rich neighborhoods.
How long does it take to build an ADU in Mountain View?
The full ADU timeline in Mountain View is typically 10-16 months from design start to move-in. Permit review takes 4-8 weeks for a complete application. Construction runs 4-8 months depending on size and complexity. Garage conversions are faster, with total timelines of 6-10 months.
Do I need to provide parking for my Mountain View ADU?
No. Mountain View does not require additional parking for any ADU type. This applies to detached ADUs, attached ADUs, JADUs, and garage conversions. You can convert your garage to an ADU without replacing the lost parking spaces.