Permit Requirements for Home Additions in Santa Clara County (2026 Guide)

Why Home Addition Permits Matter in Santa Clara County

Adding square footage to your home is one of the most impactful investments a homeowner can make. In Santa Clara County, where land values remain among the highest in the nation, building up or out on your existing lot often makes more financial sense than buying a larger property. But every home addition project begins with a critical first step: obtaining the right permits.

Skipping or mishandling permits creates risks that far outweigh the cost and timeline of doing it correctly. Unpermitted additions can trigger fines, forced demolition, insurance claim denials, and serious problems when you sell or refinance. This guide covers every aspect of the permitting process for home additions in Santa Clara County so you can plan your project with confidence.

When Is a Building Permit Required?

In Santa Clara County, a building permit is required for any home addition that increases the footprint or livable square footage of your home. This includes:

• Room additions (new bedrooms, family rooms, home offices)
• Second-story additions built above existing first-floor space
• Bump-outs that extend a room beyond the existing exterior wall
• Enclosed porches or patios converted to conditioned living space
• Garage conversions that change the use of the space

There is no minimum size threshold that exempts an addition from permitting. Even a small sunroom extension requires a building permit because it involves structural, electrical, and energy code compliance.

Additional Triggers for Additions Over 500 Square Feet

When your addition exceeds 500 square feet, Santa Clara County requires additional clearances before the building permit can be issued:

• School district clearance from your local school district
• Fire district clearance if your property falls within the South Santa Clara County Fire District jurisdiction or another fire authority
• Planning land use application if the addition triggers design review, falls within a scenic road corridor, or is located in a historic district

These additional requirements add time to the front end of the process, so identifying them early is essential.

City vs. County Jurisdiction: Where to Apply

One of the most common points of confusion for Santa Clara County homeowners is determining which jurisdiction handles their building permit. The answer depends on whether your property is in an incorporated city or an unincorporated area.

Incorporated Cities

If your home is within city limits, you apply for your building permit through that city’s building department. Santa Clara County contains 15 incorporated cities, each with its own permit office, fee schedule, and review timeline:

• San Jose, Sunnyvale, Santa Clara, Mountain View, Palo Alto
• Milpitas, Cupertino, Campbell, Los Gatos, Saratoga
• Los Altos, Los Altos Hills, Morgan Hill, Gilroy, Monte Sereno

Each city sets its own permit fees, plan check timelines, and submission requirements. Some cities, like Palo Alto and Los Altos Hills, have more stringent design review requirements that add time and cost to the process.

Unincorporated County Areas

If your property is in an unincorporated area (such as parts of the Santa Cruz Mountains, San Martin, or areas near Stanford), your permits are handled by the Santa Clara County Department of Planning and Development. You can verify your property’s jurisdiction through the County’s Property Profile application or by contacting the department at (408) 299-5700.

Why Jurisdiction Matters

Fee schedules, plan check timelines, and specific documentation requirements differ between jurisdictions. A project in San Jose may have a different fee structure and faster turnaround than the same project in Saratoga. Your design-build team should be familiar with the specific requirements of your jurisdiction to avoid delays.

Required Documents and Plans

A complete building permit application for a home addition in Santa Clara County requires several categories of documentation. Submitting a complete package on the first attempt is the single most effective way to avoid delays.

Architectural Plans

Your plan set must include:

• Site plan showing the existing structure, proposed addition, property lines, setbacks, and easements
• Floor plans for both existing and proposed conditions
• Exterior elevations showing the addition’s relationship to the existing structure
• Building sections detailing wall assemblies, roof connections, and ceiling heights
• Roof plan showing drainage, materials, and structural connections
• Construction details for footings, connections, waterproofing, and finishes

Plans must be drawn to scale on sheets sized between 18” x 24” and 24” x 36”.

Structural Engineering

A licensed structural engineer must provide:

• Structural calculations demonstrating that the addition and any modified existing structure meet current California Building Code (CBC) requirements
• Foundation design sized for local soil conditions
• Framing plans with member sizes, connections, and load paths
• Lateral force analysis for seismic resistance (critical in the Bay Area’s Seismic Design Category D or E zones)

Title 24 Energy Compliance

California’s Title 24, Part 6 (the Energy Code) applies to all home additions. As of January 1, 2026, the 2025 Energy Code is in effect, bringing roughly 30% more stringent requirements compared to the 2022 cycle. Key requirements include:

• Insulation standards: Ceiling/roof insulation of R-22 or better (0.043 U-factor), plus increased wall insulation requirements
• Window performance: Improved U-factor and Solar Heat Gain Coefficient (SHGC) ratings for all new windows
• HVAC efficiency: Updated equipment efficiency standards that encourage heat pump systems for heating, cooling, and water heating
• Duct sealing: Mandatory duct sealing verification for new and modified HVAC systems
• HERS verification: A certified HERS (Home Energy Rating System) rater must verify post-installation efficiency for mechanical changes, additions, and major remodels

You can comply with Title 24 through either the prescriptive method (following a checklist of specific requirements) or the performance method (using energy modeling software to demonstrate that the addition meets the overall energy budget for your climate zone). Santa Clara County falls within Climate Zone 4, which has specific requirements tailored to the region’s moderate Mediterranean climate.

Mechanical, Electrical, and Plumbing (MEP) Drawings

Depending on the scope of your addition, you may need separate plans for:

• Electrical: Panel capacity analysis, circuit layouts, lighting plans, and EV-ready wiring (now required for new construction under the 2025 code)
• Plumbing: Supply and drain layouts for any new fixtures, water heater sizing
• Mechanical (HVAC): Equipment specifications, duct layouts, and Manual J load calculations

Geotechnical Report

A geotechnical (soil) report is required for additions larger than 1,200 square feet. The report evaluates soil bearing capacity, expansive soil conditions, groundwater levels, and seismic hazards. It informs foundation design and grading requirements. Even for smaller additions, your structural engineer or the building department may request a soils report based on site-specific conditions.

Additional Documentation

Depending on your property and project, you may also need:

• “Will Serve” letter from your local water provider confirming service capacity
• Sanitary sewer clearance from your sewer district or a clearance letter from the Department of Environmental Health (for properties with onsite septic systems or wells)
• Habitat plan documentation if your property is within a designated habitat area
• Tree removal permits if protected trees must be removed or significantly trimmed

The Application Process Step by Step

Step 1: Pre-Application Research

Before investing in full plan development, confirm your project’s feasibility:

• Verify your property’s zoning, setback requirements, lot coverage limits, and height restrictions
• Determine whether a planning entitlement (design review, variance, or conditional use permit) is required in addition to the building permit
• Contact the building department at (408) 299-5700 or visit the public counter to discuss your project with a planner

Step 2: Plan Preparation

Engage a licensed architect and structural engineer to prepare your complete plan set. For energy compliance, you will also need a Title 24 energy consultant. A design-build firm like Custom Home coordinates all of these disciplines in-house or through established partnerships, ensuring that plans are complete and consistent across all disciplines.

Step 3: Online Submission

Submit your application through the jurisdiction’s online permit portal. For unincorporated Santa Clara County, this is the Public Permit Portal. Create a development application by selecting “Development Permit Request” and upload your completed Development Services Intake Form along with the full plan set. Individual files should not exceed 100 MB, and plans can be separated by discipline (architectural, structural, civil, landscape).

Step 4: Plan Check Review

The building department reviews your plans for code compliance. At the county level, initial plan check typically takes four to six weeks for residential additions. Reviewers check structural, energy, fire safety, accessibility, and zoning compliance. If corrections are needed, you will receive a plan check comment letter listing all required revisions.

Step 5: Plan Corrections and Resubmittal

Address all plan check comments, revise your drawings, and resubmit. The correction review cycle is typically shorter (one to three weeks), but multiple rounds of corrections can significantly extend the overall timeline.

Step 6: Fee Payment and Permit Issuance

Once plans are approved, the building department calculates your final fees. Plan check and planning fees are due at the time of application, while building permit fees and other charges can be paid when the permit is issued. After all fees are paid, your building permit is issued and construction can begin.

Understanding Permit Fees

Permit fees for home additions in Santa Clara County are based on the project’s construction valuation, not a flat rate. The fee structure includes:

• Building permit fee: Calculated from a tiered schedule based on total project valuation
• Plan check fee: 75% of the calculated building permit fee for residential projects
• School district fees: Typically assessed per square foot of new construction
• Fire district fees: If applicable to your jurisdiction
• Utility connection fees: For new water, sewer, or electrical service connections
• HERS testing fee: Paid to a certified rater for Title 24 verification

For a typical home addition valued between $200,000 and $500,000 in construction cost, total permit-related fees generally range from $5,000 to $20,000 or more, depending on the jurisdiction and project scope. The Santa Clara County Department of Planning and Development publishes its current fee schedule for FY 2025-2026 on its website.

Required Inspections During Construction

Once your permit is issued, your project must pass a series of inspections at key construction milestones. Never cover any work until it has been approved by a building inspector.

Typical Inspection Sequence

1. Foundation/footing inspection: Verify excavation, formwork, and steel reinforcement before concrete is poured
2. Underfloor/underslab: Inspect plumbing, moisture barriers, and gravel base before the slab is poured
3. Framing inspection: Verify structural framing, shear walls, hold-downs, and connections match approved plans
4. Rough electrical: Inspect wiring, boxes, panel connections, and grounding before walls are closed
5. Rough plumbing: Inspect supply lines, drain/waste/vent piping, and water heater connections
6. Rough mechanical: Inspect HVAC ductwork, equipment installation, and refrigerant lines
7. Insulation and energy: Verify insulation R-values, air sealing, and window specifications match the Title 24 report
8. Drywall/lath: In some jurisdictions, an inspection is required after drywall is hung but before taping
9. Final inspection: A comprehensive walkthrough verifying all work is complete, smoke and carbon monoxide detectors are installed, and the addition is safe for occupancy

Important Inspection Rules

• Work must match the approved plans exactly. If field conditions require changes, your design professional must revise the plans and submit them to the county for approval before calling for an inspection.
• Schedule inspections before covering any work. Covering unapproved work can result in a requirement to remove finished materials for inspection.
• Permits expire if more than 180 days pass between approved inspections. The first extension request carries no fee, but subsequent extensions may incur charges.

Common Reasons for Permit Delays

Understanding the most frequent causes of delay helps you avoid them:

• Incomplete applications: Missing documents, inconsistent plan sheets, or incorrect forms
• Zoning non-compliance: Setback violations, lot coverage exceedance, or height limit issues not identified before submission
• Structural calculation errors: Undersized members, missing connection details, or incomplete lateral analysis
• Title 24 non-compliance: Energy calculations that do not meet the 2025 code requirements
• Multiple correction cycles: Each round of plan check comments adds one to three weeks
• Missing clearances: School district, fire district, or utility clearances not obtained before or during plan check

How Custom Home Handles the Entire Permit Process

Navigating Santa Clara County’s permitting requirements is one of the most complex parts of any home addition project. At Custom Home, we manage the entire process as part of our Phase 1 (Design) scope. Our team prepares complete, code-compliant plans, coordinates with structural engineers and Title 24 consultants, submits the application, responds to plan check comments, and schedules all required inspections during construction.

This approach delivers two clear benefits. First, our experience with local building departments means we submit plans that pass plan check with minimal corrections, reducing your timeline by weeks. Second, you have a single point of contact for the entire process rather than coordinating between separate architects, engineers, energy consultants, and permit expediters.

If you are planning a home addition in Santa Clara County and want a team that handles permits, design, and construction under one roof, contact us today to discuss your project. We will walk you through the requirements specific to your property and jurisdiction so you know exactly what to expect before you commit.