Complete Guide to Building an ADU in Los Gatos
Los Gatos combines small-town character with high property values and strong rental demand, making ADUs an attractive investment for homeowners. Building an ADU in Los Gatos costs $250,000-$500,000+ in 2026. The town follows California state ADU law with ministerial approval and standardized setback requirements. Hillside properties face additional engineering and drainage considerations. This guide covers Los Gatos ADU regulations, lot types, costs, popular designs, the permit process, and how Custom Home Design and Build serves Los Gatos homeowners with a full design-build approach.
What are the ADU regulations in Los Gatos?
Los Gatos 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. Hillside lots may require additional engineering for foundation and drainage. Construction costs range from $250,000 to $500,000+.
Why Los Gatos Homeowners Are Building ADUs
Los Gatos occupies a unique position in the South Bay housing market. The town’s walkable downtown, proximity to the Santa Cruz Mountains, and top-rated schools create consistent demand from families and professionals willing to pay a premium to live here. Median home values sit near $2.5 million, and rental rates reflect the scarcity of housing in a community that has limited new construction.
For homeowners, an ADU addresses multiple needs at once. Rental income from a one-bedroom unit in Los Gatos ranges from $2,500 to $3,500 per month, translating to $30,000 to $42,000 in annual gross income. An ADU also provides housing for aging parents who want to be nearby, space for adult children, or a dedicated home office or creative studio. And the property value increase from a well-built ADU further strengthens the investment case.
Los Gatos’s housing stock is well positioned for ADU construction. Many properties have generous lots, especially in the flatland neighborhoods near downtown. Even hillside properties can accommodate ADUs with proper engineering and design. California state law has streamlined the approval process, removing barriers that previously made ADU construction difficult in towns like Los Gatos.
Los Gatos 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 of 850 sqft for studios/one-bedrooms and 1,000 sqft for two-bedrooms apply, ensuring homeowners can build functional units regardless of the 50% calculation.
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 for conversions of existing structures
Existing garages or accessory buildings that already sit within 4 feet of a property line can be converted to ADUs without relocation.
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
Los Gatos is primarily served by bus transit rather than rail, so the 18-foot transit proximity allowance applies to fewer properties than in cities like Sunnyvale or Mountain View. However, the standard 16-foot height limit still accommodates comfortable single-story ADUs, and properties with matching roof pitches may qualify for taller designs.
Parking
No additional parking is required for any ADU type in Los Gatos. Garage conversions can proceed without replacing the converted parking spaces.
Units Allowed
On a single-family lot:
- One ADU (detached or attached) plus one JADU
Lot Types and ADU Feasibility in Los Gatos
Flatland Lots Near Downtown (6,000-12,000 sqft)
The neighborhoods between downtown Los Gatos and Highway 85 contain single-family homes on relatively flat lots. These properties are ideal for ADU construction: level terrain simplifies foundation work, utilities are accessible, and rear yards typically have room for a 600-1,000 sqft detached unit.
Many of these homes have existing detached garages that can be converted to ADUs at lower cost than new construction, or demolished and replaced with a purpose-built unit.
Larger Flatland Lots (12,000-20,000+ sqft)
Properties along Los Gatos Boulevard, near the end of Shannon Road (flatland portions), and in other established neighborhoods sometimes have lots exceeding 12,000 sqft. These lots provide maximum flexibility: a full 1,200 sqft detached ADU with private outdoor space, a separate entrance, and generous landscaping buffers.
Hillside Lots
Properties in the foothills above downtown Los Gatos present unique opportunities and challenges for ADU construction. The terrain requires:
- Geotechnical investigation. A soils report determines foundation requirements and identifies potential slope stability issues.
- Custom foundation design. Hillside ADUs often need pier-and-grade-beam or stepped foundations rather than simple slabs.
- Drainage and erosion control. Proper grading and drainage prevent water damage to the ADU and neighboring properties.
- Access planning. Construction equipment access on steep driveways requires advance planning.
These requirements add cost, but hillside ADUs can take advantage of views and terrain to create distinctive living spaces.
Corner Lots
Corner lots in Los Gatos provide dual-access opportunities. The ADU can face a side street with its own separate entrance, creating privacy for both the main home and the ADU.
ADU Costs in Los Gatos
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-$290,000 | 10-14 months |
| Mid-Size Detached ADU | 600-900 sqft | $290,000-$390,000 | 10-16 months |
| Full-Size Detached ADU | 900-1,200 sqft | $390,000-$500,000+ | 12-18 months |
| Attached ADU | 400-800 sqft | $190,000-$330,000 | 8-14 months |
| Junior ADU (JADU) | Up to 500 sqft | $80,000-$150,000 | 4-8 months |
| Hillside Detached ADU | 600-1,000 sqft | $350,000-$550,000+ | 12-20 months |
Cost Factors Specific to Los Gatos
- Hillside premium. Geotechnical reports, custom foundations, retaining walls, and drainage systems add $25,000-$70,000 to hillside projects.
- Tree preservation. Los Gatos’s Protected Tree Ordinance may require arborist reports and root protection plans if the ADU footprint affects protected trees. Tree removal permits, when necessary, involve replacement planting requirements.
- Premium finishes. Los Gatos homeowners typically expect quality materials in their ADUs, especially if the unit will house family members. Hardwood or high-quality LVP flooring, stone countertops, and attractive cabinetry are standard.
- Design compatibility. An ADU that complements the architectural style of the primary home and the surrounding neighborhood adds property value. Matching rooflines, exterior materials, and window proportions is worth the investment.
Sample Budget: 750 Sqft Detached ADU (Flatland Lot)
A representative budget for a two-bedroom detached ADU on a flat lot in Los Gatos:
| Budget Category | Estimated Cost |
|---|---|
| Architecture and engineering | $16,000-$26,000 |
| Permits and fees | $12,000-$22,000 |
| Site preparation | $6,000-$12,000 |
| Foundation (slab on grade) | $20,000-$32,000 |
| Framing and structural | $42,000-$62,000 |
| Roofing | $10,000-$16,000 |
| Electrical (including panel upgrade) | $16,000-$26,000 |
| Plumbing | $14,000-$24,000 |
| HVAC (mini-split) | $8,000-$14,000 |
| Insulation and drywall | $14,000-$22,000 |
| Flooring | $10,000-$16,000 |
| Kitchen (complete) | $26,000-$42,000 |
| Bathroom(s) | $18,000-$30,000 |
| Windows and doors | $10,000-$16,000 |
| Exterior finish | $12,000-$20,000 |
| Utility connections | $18,000-$32,000 |
| Landscaping | $5,000-$10,000 |
| Total estimated range | $257,000-$422,000 |
Permit Process in Los Gatos
Los Gatos processes ADU applications ministerially, consistent with California state law. The Town of Los Gatos Community Development Department handles the review.
Steps
- Design. Work with a design-build firm to create architectural plans, structural engineering, and Title 24 energy compliance documentation.
- Application submittal. Submit plans and application to the Community Development Department.
- Plan review. Staff reviews for building code compliance. State law mandates 60-day processing for complete applications.
- Corrections (if needed). Address any plan check corrections and resubmit.
- Permit issuance. Pay fees and receive the building permit.
- Construction. Build with required inspections at each phase: foundation, framing, rough mechanical, insulation, and final.
- Final inspection. Town inspects and issues certificate of occupancy.
Timeline
| Phase | Duration |
|---|---|
| Design and engineering | 4-8 weeks |
| Geotechnical report (hillside lots) | 2-4 weeks |
| Permit review | 4-8 weeks |
| Construction | 4-8 months |
| Total (flatland) | 10-16 months |
| Total (hillside) | 12-20 months |
Popular ADU Designs for Los Gatos
Craftsman-Inspired One-Bedroom (650-750 sqft)
A design that complements Los Gatos’s older residential character. Covered front porch, pitched roof, wood or composite siding, and details that echo the Craftsman homes found near downtown. Interior: open living-kitchen area, one bedroom, full bathroom.
Contemporary Two-Bedroom (900-1,100 sqft)
Clean lines, large windows, and modern materials create a bright, efficient living space. Two bedrooms, one bathroom, full kitchen, and a living area. This design works well on larger lots where the ADU can have its own patio and outdoor space.
Garden Studio (400-500 sqft)
A compact unit designed to blend with landscaping. Ideal for a home office, art studio, or small rental. Can include a kitchenette and bathroom to qualify as an ADU, or be designed as a non-habitable accessory structure.
Garage Conversion (400-500 sqft)
Converting an existing detached garage into a studio or one-bedroom ADU. The existing structure provides the shell, and the conversion adds insulation, finished interiors, kitchen, bathroom, windows, and a separate entrance. The most affordable and fastest ADU option in Los Gatos.
Rental Income Potential
Los Gatos’s desirable location supports strong rental rates:
| ADU Size | Bedrooms | Monthly Rent Range | Annual Gross Income |
|---|---|---|---|
| 400-500 sqft | Studio | $2,200-$2,800 | $26,400-$33,600 |
| 650-750 sqft | 1 BR | $2,500-$3,500 | $30,000-$42,000 |
| 900-1,100 sqft | 2 BR | $3,200-$4,200 | $38,400-$50,400 |
These rates reflect 2026 market conditions. Actual rents depend on finish quality, location within Los Gatos, included amenities, and overall market conditions.
Why Custom Home Design and Build
Custom Home Design and Build has been building ADUs across Los Gatos and the South Bay since 2005. We understand the town’s lot conditions, hillside engineering requirements, and the design sensibility that Los Gatos homeowners expect. Our portfolio includes both flatland and hillside ADU projects throughout the community.
Our design-build approach means one contract, one team, one point of accountability:
- Architectural design tailored to your lot and goals
- Structural and geotechnical engineering
- Permit application and coordination with the town
- Full construction with licensed, experienced crews
- Project management from design through final inspection
Start Your Los Gatos ADU
Whether you are building for rental income, family housing, or a combination of both, an ADU on your Los Gatos property is a strong investment. The first step is evaluating your lot’s potential.
Contact Custom Home Design and Build for a free ADU consultation. We will assess your property, review setbacks and site conditions, and present design options that fit your goals 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 Los Gatos?
ADU construction in Los Gatos costs $250,000-$500,000+ in 2026. Garage conversions start around $120,000-$200,000. A 600 sqft detached ADU typically runs $250,000-$340,000. A full 1,200 sqft detached ADU costs $400,000-$500,000+. Hillside properties add 10-20% to costs due to foundation, grading, and drainage requirements.
Are there special rules for ADUs on hillside lots in Los Gatos?
Hillside lots in Los Gatos may require geotechnical reports, custom foundation design, retaining walls, and drainage systems for ADU construction. While California state ADU law limits the ability of cities to impose additional requirements, site-specific engineering is necessary to ensure structural safety on sloped properties. These requirements add cost and timeline but do not prevent ADU construction.
How long does it take to build an ADU in Los Gatos?
The full ADU timeline in Los Gatos 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 ADU size and site conditions. Hillside projects may require additional engineering time.
Can I build an ADU in Los Gatos if my property is near downtown?
Yes. Properties in Los Gatos's flatland neighborhoods near downtown are well suited for ADUs. These lots typically have level terrain, straightforward utility access, and ample rear yard space. State ADU law applies to all residentially zoned properties with an existing or proposed single-family home.