Complete Guide to Building an ADU in Cupertino
Cupertino's residential neighborhoods, anchored by Apple Park and top-rated schools, are among the most valuable in Silicon Valley. Building an ADU on your Cupertino property costs $250,000-$500,000+ in 2026, depending on size, type, and finish level. The city follows California state ADU law with ministerial approval for compliant projects, 4-foot side and rear setbacks for detached ADUs, and no additional parking requirements. This guide covers Cupertino-specific regulations, lot requirements, costs, popular ADU designs, permit timelines, and how Custom Home Design and Build handles ADU projects from design through construction.
What are the ADU regulations in Cupertino?
Cupertino 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 with no discretionary review. No additional parking is required. Construction costs range from $250,000 to $500,000+ depending on size and type.
Why Cupertino Homeowners Are Building ADUs
Cupertino’s residential market is defined by high property values, strong demand from tech workers (driven by Apple Park and neighboring employers), and a limited supply of housing. Median home values exceed $3 million, and the combination of top-rated schools in the Cupertino Union and Fremont Union districts with proximity to major tech campuses keeps demand consistently high.
For homeowners, an ADU (Accessory Dwelling Unit) serves multiple purposes. It provides rental income in one of the country’s most expensive rental markets, where a one-bedroom unit in Cupertino rents for $2,500 to $3,500 per month. It creates space for aging parents or adult children. It adds significant property value. And under recent California laws, ADUs can even be sold as separate condominium units on some properties.
Cupertino follows California’s statewide ADU regulations, which streamline the approval process and limit the city’s ability to impose restrictions beyond state law. This means ministerial approval (no discretionary design review), standardized setback requirements, and relatively predictable timelines.
Cupertino ADU Regulations
Size Limits
ADU size limits in Cupertino follow state law:
| 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 (must be within the existing home) |
The state-mandated minimum size is 850 sqft for a studio or one-bedroom and 1,000 sqft for a two-bedroom unit. This floor ensures that even on properties with smaller primary homes, homeowners can build a functional ADU.
Setback Requirements
- 4-foot side setbacks for new detached and attached ADUs
- 4-foot rear setbacks for new detached and attached ADUs
- Front yard setback per the R-1 zoning district (typically 20 feet)
Conversions of existing structures (garage conversions, for example) do not need to meet the 4-foot setback requirement if the existing structure is already closer to the property line. This makes garage conversions particularly straightforward in Cupertino.
Height Limits
- 16 feet for standard detached ADUs
- 18 feet if within half a mile of a major transit stop
- Taller allowances if the ADU’s roof pitch matches the primary home
Cupertino is served by several VTA bus routes, and portions of the city may qualify for the 18-foot height allowance based on proximity to transit. Check your property’s eligibility with the Community Development Department.
Parking
No additional parking is required for any ADU type in Cupertino. This applies to detached ADUs, attached ADUs, JADUs, and garage conversions. Even if you convert your garage to an ADU, eliminating existing parking spaces, no replacement parking is required.
Units Allowed
On a single-family lot, you may build:
- One ADU (detached or attached) plus one JADU
This means you could have your primary home, a 1,200 sqft detached ADU in the backyard, and a 500 sqft JADU within the main house, all on a single property.
Cupertino Lot Types and ADU Feasibility
Standard R-1 Lots (6,000-8,000 sqft)
Most Cupertino homes sit on lots in this range. A detached ADU with 4-foot setbacks fits well in the rear yard of these properties, though the available footprint depends on the existing home’s position, driveway location, and any mature trees.
A 600-800 sqft detached ADU is the sweet spot for these lots: large enough for a comfortable one-bedroom or two-bedroom unit, small enough to leave usable yard space.
Larger Lots (10,000+ sqft)
Properties along the foothills or in established neighborhoods with larger lots have more flexibility. A full 1,200 sqft detached ADU is feasible, and there is often room to design around existing landscaping and outdoor living areas.
Corner Lots
Corner lots in Cupertino offer unique ADU opportunities because they have two street-facing sides. A detached ADU can be positioned with its own street presence and separate entrance, improving privacy for both the main home and the ADU.
ADU Costs in Cupertino
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 | $120,000-$200,000 | 6-10 months |
| Small Detached ADU | 400-600 sqft | $200,000-$300,000 | 10-14 months |
| Mid-Size Detached ADU | 600-900 sqft | $300,000-$400,000 | 10-16 months |
| Full-Size Detached ADU | 900-1,200 sqft | $400,000-$500,000+ | 12-18 months |
| Attached ADU | 400-800 sqft | $200,000-$350,000 | 8-14 months |
| Junior ADU (JADU) | Up to 500 sqft | $80,000-$150,000 | 4-8 months |
What Drives ADU Costs
- Foundation type. Slab-on-grade is the most affordable. Raised foundations or pier-and-beam systems on sloped sites cost more.
- Utility connections. Extending water, sewer, gas, and electrical to a detached ADU involves trenching, connection fees, and potentially upgrading the main panel. Budget $15,000-$40,000 for utility work.
- Site preparation. Removing an existing structure, grading, and tree work add to the base cost.
- Finishes. Cupertino’s market expects quality. Even rental ADUs benefit from durable, attractive materials that command higher rents and reduce maintenance.
- Kitchen and bathroom. These are the most expensive rooms per square foot. A full kitchen with quality appliances, countertops, and cabinetry costs $25,000-$50,000 in an ADU.
Sample Budget: 750 Sqft Detached ADU
A representative budget for a detached two-bedroom ADU on a standard Cupertino lot:
| Budget Category | Estimated Cost |
|---|---|
| Architecture and engineering | $18,000-$28,000 |
| Permits and fees | $12,000-$22,000 |
| Site preparation and grading | $8,000-$15,000 |
| Foundation (slab on grade) | $20,000-$32,000 |
| Framing and structural | $40,000-$60,000 |
| Roofing | $10,000-$16,000 |
| Electrical (including panel upgrade) | $18,000-$28,000 |
| Plumbing | $15,000-$25,000 |
| HVAC (mini-split system) | $8,000-$14,000 |
| Insulation and drywall | $14,000-$22,000 |
| Flooring | $10,000-$16,000 |
| Kitchen (complete) | $28,000-$45,000 |
| Bathroom(s) | $18,000-$30,000 |
| Windows and doors | $10,000-$16,000 |
| Exterior finish | $12,000-$20,000 |
| Utility connections and trenching | $20,000-$35,000 |
| Landscaping | $5,000-$10,000 |
| Total estimated range | $266,000-$434,000 |
Permit Process
Cupertino processes ADU applications ministerially, meaning the review is based on objective standards rather than subjective design judgment. If your plans meet the code, the city approves them.
Steps
- Design. Work with a design-build firm to create architectural plans, structural engineering, and Title 24 energy compliance documentation.
- Application submittal. Submit plans to the Cupertino Community Development Department along with application fees.
- Plan review. City staff reviews for code compliance. State law requires processing within 60 days of a complete application.
- Corrections (if needed). If the plans require revisions, the city issues a correction letter. Resubmittals restart the review clock.
- Permit issuance. Once approved, pay permit fees and receive your building permit.
- Construction. Build the ADU with required inspections at each phase.
- Final inspection and occupancy. City inspects the completed ADU and issues a certificate of occupancy.
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 Cupertino
Modern One-Bedroom (600-700 sqft)
An open-concept living and kitchen area with a separate bedroom and full bathroom. This layout maximizes livable space and is ideal for rental units. A ductless mini-split system handles heating and cooling efficiently.
Two-Bedroom Family Unit (800-1,000 sqft)
Two bedrooms, one or two bathrooms, a full kitchen, and a living area. This design serves families with aging parents, adult children returning home, or tenants who need more space. The second bedroom adds significant rental value.
Studio/One-Bedroom with Home Office (500-700 sqft)
A flexible layout that combines living space with a dedicated work area. Popular in Cupertino’s tech-driven market where renters may work from home part of the week.
Garage Conversion (400-500 sqft)
Converting an existing garage into a studio or one-bedroom ADU is the fastest and most affordable path. The existing structure provides a shell, and the conversion adds insulation, flooring, plumbing, kitchen, bathroom, windows, and a separate entrance.
Why Custom Home Design and Build
Custom Home Design and Build has been constructing ADUs across the South Bay since 2005. Our Cupertino ADU projects benefit from our familiarity with the city’s planning department, local building requirements, and the design expectations of Cupertino homeowners.
As a design-build firm, we handle everything under one roof:
- Architectural design tailored to your lot and goals
- Structural engineering for foundation and framing
- Permit application and city coordination
- Full construction with licensed crews
- Project management from first sketch to final inspection
This single-team approach eliminates the coordination problems that arise when homeowners hire separate architects, engineers, and contractors. It also means your design and budget are aligned from the start.
Start Your Cupertino ADU
An ADU on your Cupertino property is one of the highest-value improvements you can make. Whether you are building for rental income, family housing, or long-term property value, the first step is understanding what your specific lot allows.
Contact Custom Home Design and Build for a free ADU consultation. We will assess your property, review setbacks and utility access, and walk you through design options that fit your lot and budget. Call (888) 306-1688 or complete our contact form to get started.
Frequently Asked Questions
How much does it cost to build an ADU in Cupertino?
ADU construction in Cupertino costs $250,000-$500,000+ in 2026. Garage conversions start around $120,000-$200,000. A 600 sqft detached ADU typically runs $250,000-$350,000. A full-size 1,200 sqft detached ADU costs $400,000-$500,000+. Costs depend on foundation type, utility connections, finishes, and site-specific conditions.
What setbacks are required for an ADU in Cupertino?
New detached and attached ADUs in Cupertino require 4-foot side and rear setbacks per California state law. The underlying front yard setback from the R-1 zoning district still applies. Conversions of existing structures (like garages) that are already within setbacks do not need to be brought into compliance.
How long does it take to get an ADU permit in Cupertino?
Cupertino must process complete ADU applications within 60 days per state law. Most applications are reviewed in 4-8 weeks if the submittal is complete and code-compliant. Incomplete applications or plans requiring corrections will take longer. The full timeline from design start to move-in is typically 10-16 months.
Can I build a two-story ADU in Cupertino?
Height limits for ADUs in Cupertino follow state law: 16 feet for a standard detached ADU, 18 feet if within half a mile of a major transit stop, and potentially taller if the roof pitch matches the primary home. Two-story designs are possible under the 18-foot or taller allowance, but the height limit and lot conditions determine feasibility for your specific property.