How Much Does a Home Addition Cost in Los Gatos? (2026)
Home additions in Los Gatos cost $325-$575 per square foot in 2026, reflecting the town's premium housing market and distinctive regulatory environment. Ground-floor additions average $325-$450/sqft. Second-story additions run $400-$575/sqft. Los Gatos's Architecture and Site Review process, hillside development standards, and high-end finish expectations add 15-25% above the broader South Bay average. With median home prices near $2.8 million, adding on remains far more practical than buying larger.
How much does a home addition cost in Los Gatos?
Home additions in Los Gatos cost $325-$575 per square foot in 2026. A 400 sqft bedroom addition runs $130K-$180K. Second-story additions average $320K-$575K+ for 800-1,200 sqft. Los Gatos's Architecture and Site Review process and hillside development standards add time and cost compared to many neighboring cities.
What Does a Home Addition Cost in Los Gatos?
Los Gatos is one of the most desirable residential communities in Silicon Valley. Nestled in the foothills of the Santa Cruz Mountains, the town combines a walkable downtown, excellent schools in the Los Gatos Union and Los Gatos-Saratoga Joint Union districts, and a mix of flatland neighborhoods and hillside estates. With a median home price near $2.8 million, homeowners here are invested in their properties for the long term.
Home additions in Los Gatos cost $325-$575 per square foot in 2026. That is 15-25% above the broader South Bay average, reflecting the town’s regulatory environment, premium finish expectations, and the added complexity of building on hillside lots.
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 home addition pricing, see our home addition cost guide.
Cost Breakdown by Addition Type
The type of addition shapes both your per-square-foot cost and your total budget. Here is what Los Gatos homeowners are paying in 2026:
| Addition Type | Cost Per Sqft | Typical Size | Total Cost Range | Timeline |
|---|---|---|---|---|
| Bedroom Addition | $325-$450/sqft | 200-400 sqft | $65,000-$180,000 | 5-9 months |
| Bathroom Addition | $400-$550/sqft | 60-150 sqft | $90,000-$165,000 | 4-7 months |
| Family Room Addition | $325-$450/sqft | 300-600 sqft | $97,500-$270,000 | 6-10 months |
| Second-Story Addition | $400-$575/sqft | 800-1,500 sqft | $320,000-$575,000+ | 9-15 months |
| Master Suite (2nd Floor) | $425-$575/sqft | 500-800 sqft | $225,000-$425,000 | 8-13 months |
| Bump-Out / Extension | $275-$400/sqft | 50-200 sqft | $14,000-$80,000 | 3-5 months |
These ranges cover construction costs. Design fees, engineering, permits, and the Architecture and Site Review process add to these totals.
Cost Breakdown by Component
Foundation and Structural Work: 15-28%
Foundation costs in Los Gatos vary dramatically between flatland and hillside properties. Flatland additions require standard footings at $15,000-$35,000. Hillside lots may need engineered retaining walls, deepened footings, and specialized drainage, pushing foundation costs to $30,000-$60,000 or more. Second-story additions on either terrain require reinforcing the existing foundation at $15,000-$40,000.
Framing and Exterior: 20-30%
Los Gatos homeowners expect exterior materials that blend with the town’s architectural character. Whether your home is a Craftsman bungalow near downtown or a contemporary hillside residence, the addition must look intentional. Premium siding, architectural roofing, and quality windows (Marvin, Pella, or equivalent) are standard here. Budget $35,000-$75,000 for a 400 sqft addition.
Mechanical Systems: 15-20%
Electrical, plumbing, and HVAC costs in Los Gatos are comparable to the broader South Bay: panel upgrades at $3,500-$9,000, plumbing rough-in at $8,000-$16,000, and HVAC at $9,000-$20,000. Hillside properties sometimes require upgraded electrical service from PG&E, adding $5,000-$15,000.
Interior Finishes: 25-35%
Finish selections drive a significant portion of your budget. Los Gatos homeowners typically choose mid-range to premium materials: hardwood or engineered hardwood flooring, custom cabinetry, quartz or stone countertops, and quality fixtures. Standard finishes run $60-$90/sqft. Mid-range finishes cost $90-$130/sqft. Premium finishes reach $130-$190/sqft.
What Drives Costs in Los Gatos
Architecture and Site Review
Los Gatos requires Architecture and Site Review for most home additions that alter the exterior appearance or add significant square footage. The review board evaluates:
- Architectural compatibility with the neighborhood
- Building mass and bulk relative to neighboring homes
- Privacy impacts from new windows, decks, or elevated structures
- Landscaping and site integration
This process adds $5,000-$12,000 in professional fees (architect presentations, potential redesigns) and 8-16 weeks to your timeline. Projects that receive neighbor objections may require additional hearings and modifications.
Hillside Development Standards
Properties in Los Gatos’s hillside areas face additional regulations:
- Height restrictions based on slope angle
- Additional setbacks beyond standard zoning requirements
- Grading limits that restrict the amount of earth that can be moved
- Mandatory geotechnical reports ($4,000-$8,000) to evaluate slope stability
- Drainage plans to manage water runoff on sloped sites
Hillside additions cost 15-30% more than comparable flatland projects. Access challenges (narrow roads, steep driveways) increase material delivery costs and construction timelines.
Premium Market Expectations
With homes in neighborhoods like Almond Grove, Belwood, and the hills above town selling for $2-$5 million or more, the bar for quality is high. An addition that falls short of the existing home’s finish level will stand out for the wrong reasons. Most Los Gatos projects include:
- Hardwood flooring to match or complement the existing home
- Custom or semi-custom cabinetry
- Natural stone or premium quartz countertops
- Integrated smart home features
- Landscaping that ties the addition into the existing yard
Older Homes in Downtown Area
Many homes near downtown Los Gatos date to the early 1900s through the 1950s. These older structures often need electrical upgrades, plumbing replacement, or structural reinforcement before the addition work can begin. Budget $8,000-$30,000 for pre-construction remediation on homes built before 1970.
Permits and Regulations
Permit Fees and Soft Costs
| Cost Category | Estimated Range | Notes |
|---|---|---|
| Architectural design | $18,000-$45,000 | Includes Architecture and Site Review preparation |
| Structural engineering | $5,000-$15,000 | Required for all additions, especially second-story |
| Building permits | $8,000-$25,000 | Based on project valuation |
| Plan check fees | $5,000-$15,000 | Typically 65-80% of building permit fee |
| Geotechnical report | $4,000-$8,000 | Required for hillside lots, recommended for all |
| Architecture and Site Review fees | $2,000-$6,000 | Town application and hearing fees |
| Contingency (10-15%) | Varies | Essential for older homes and hillside properties |
Total soft costs typically add $50,000-$120,000 to your construction budget for a major addition in Los Gatos.
Key Zoning Rules
- Maximum lot coverage: Varies by zone, typically 35-45%
- Floor area ratio (FAR): Ranges from 35% to 45% depending on lot size and zone
- Side setbacks: 5-10 feet depending on lot width
- Rear setback: 20-25 feet
- Maximum height: 30 feet, reduced on hillside lots based on slope
- Single-story overlay zones: Some neighborhoods restrict two-story construction
Always verify your specific parcel’s zoning and any overlay restrictions before beginning design.
Los Gatos vs. Neighboring Cities
| City | Cost Per Sqft | Permit Timeline | Key Difference |
|---|---|---|---|
| Los Gatos | $325-$575 | 8-16 weeks | Architecture and Site Review, hillside standards |
| Saratoga | $350-$600 | 10-16 weeks | Similar premium market, design review required |
| San Jose | $250-$500 | 6-10 weeks | Lower costs due to competitive market and fewer restrictions |
| Campbell | $275-$425 | 6-10 weeks | More moderate market, faster permits |
| Monte Sereno | $375-$625 | 10-16 weeks | Smaller town with strict design review, highest in the area |
Los Gatos sits in the upper tier of South Bay pricing, comparable to Saratoga and below the most exclusive enclaves like Monte Sereno and Los Altos Hills.
Sample Budgets
Budget Example: 400 sqft Ground-Floor Bedroom + Bathroom (Flatland)
| Line Item | Cost |
|---|---|
| Construction (400 sqft at $375/sqft) | $150,000 |
| Architectural design | $15,000 |
| Structural engineering | $6,000 |
| Building permits and plan check | $12,000 |
| Architecture and Site Review | $3,000 |
| Contingency (10%) | $18,600 |
| Total | $204,600 |
Budget Example: 1,000 sqft Second-Story Addition (Hillside)
| Line Item | Cost |
|---|---|
| Construction (1,000 sqft at $500/sqft) | $500,000 |
| Architectural design (including review prep) | $35,000 |
| Structural engineering | $14,000 |
| Building permits and plan check | $22,000 |
| Geotechnical report | $6,000 |
| Architecture and Site Review fees | $5,000 |
| Temporary housing (5 months) | $20,000 |
| Contingency (12%) | $72,240 |
| Total | $674,240 |
Budget Tips for Los Gatos Homeowners
Understand Your Lot Before You Design
Flatland versus hillside is the single biggest variable in Los Gatos construction costs. Get a geotechnical report and topographic survey early. These $6,000-$12,000 in upfront costs can save $30,000+ in unexpected expenses during construction.
Work With the Review Process
The Architecture and Site Review is not optional, so build it into your timeline and budget from the start. Architects experienced with the Los Gatos process know what the review board looks for and can design accordingly, reducing the chance of costly revisions.
Match the Neighborhood
Los Gatos neighborhoods have distinct architectural characters. An addition that blends with the surrounding homes is more likely to receive smooth approval and add maximum resale value. Your architect should study the streetscape before beginning design.
Consider Phased Construction
For larger projects that push the budget, consider completing the structural scope in one phase and finishing the interior details in a second phase. This is especially useful for hillside properties where foundation and site work represent a disproportionate share of the total cost.
Why Los Gatos Homeowners Choose Custom Home
Custom Home Design and Build has been working in Los Gatos since 2005. We understand the town’s Architecture and Site Review process, the hillside development standards, and the level of craftsmanship the local market expects.
Our two-phase process is designed for regulatory environments like Los Gatos:
- Phase 1: Design. Full architectural plans, 3D renderings, material selections, and a locked-in construction price. This phase includes preparing all Architecture and Site Review submissions and managing the approval process from start to finish.
- Phase 2: Build. Permitted construction with a dedicated project manager, weekly updates, and the fixed price you approved in Phase 1.
Start Planning Your Los Gatos Home Addition
Los Gatos’s combination of excellent schools, walkable downtown, and natural beauty makes it a community where families want to stay for decades. Expanding your home is the most cost-effective way to get the space you need without leaving the neighborhood you love.
Ready to explore what a home addition would cost on your specific Los Gatos property? Contact Custom Home for a free consultation. We will visit your property, discuss your goals, and provide a realistic budget based on your lot, your neighborhood, and your plans.
Frequently Asked Questions
How much does a second-story addition cost in Los Gatos?
Second-story additions in Los Gatos cost $400-$575 per square foot in 2026, or $320,000-$575,000+ for a typical 800-1,200 sqft project. The premium over ground-floor work reflects structural reinforcement costs ($15K-$40K), the Architecture and Site Review process, and the expectation for high-quality finishes that match the town's premium housing stock.
Does Los Gatos require design review for home additions?
Yes. Los Gatos requires Architecture and Site Review for most home additions that change the exterior appearance or add significant square footage. The review evaluates architectural compatibility, neighborhood context, privacy, and bulk. Projects in the hillside areas face additional scrutiny under the Hillside Development Standards. Expect the review process to add 8-16 weeks to your permit timeline.
How long does a home addition take in Los Gatos?
Ground-floor room additions in Los Gatos take 6-10 months from design through completion. Second-story additions require 9-15 months. The Architecture and Site Review process adds 8-16 weeks before construction begins. Hillside properties may face additional geotechnical and grading requirements that extend the timeline further.
Are there special rules for additions on hillside lots in Los Gatos?
Yes. Los Gatos enforces Hillside Development Standards for properties above certain elevations or on slopes exceeding 10%. These standards limit building height, require additional setbacks, mandate geotechnical reports, and impose grading restrictions. Hillside projects typically cost 15-30% more than flatland additions due to site access challenges, retaining walls, and specialized foundation work.