ADU Construction Cost in San Diego 2026

Building an Accessory Dwelling Unit in 2026 remains one of the most strategic investments for homeowners in San Diego. Whether you plan to generate rental income, house extended family, or increase long term property value, understanding real ADU construction costs is essential before starting the process.

Prices vary widely depending on size, site conditions, design complexity, and local regulations. This guide breaks down what homeowners should realistically expect to pay in 2026 and where that money typically goes.

Average ADU Construction Cost in San Diego in 2026

In 2026, the average cost to build an ADU in San Diego typically ranges between $180,000 and $400,000 depending on size, type, and level of customization. Smaller garage conversions may fall below that range, while large detached units with premium finishes can exceed $450,000.

Construction demand remains strong, and material pricing has stabilized compared to previous years. However, labor rates, energy compliance requirements, and site specific factors continue to influence overall project costs.

Cost by ADU Type: Detached, Attached, Garage Conversion, JADU

The type of ADU you choose significantly impacts your total investment.

Detached ADU: A standalone structure built separately from the main home typically costs between $250,000 and $400,000+. These units require new foundations, full utility connections, roofing, and structural framing, which increases expenses.

Attached ADU: An addition connected to the primary residence usually ranges from $200,000 to $350,000. Costs may be slightly lower than detached units because some structural and utility systems can tie into the existing home.

Garage Conversion: Converting an existing garage into living space is often the most cost efficient option, typically ranging from $120,000 to $220,000. Since the foundation and structure already exist, major construction costs are reduced.

JADU (Junior ADU): A smaller unit created within the existing home footprint generally costs between $80,000 and $150,000, depending on upgrades and whether a separate entrance and kitchen installation are required.

Typical Cost per Square Foot in 2026

In 2026, ADU construction in San Diego averages between $350 and $600 per square foot.

Several factors affect where your project falls within that range:

• Smaller units often have higher per square foot costs due to fixed overhead expenses
• Custom finishes increase material and labor pricing
• Sloped lots or difficult access raise site preparation costs
• Energy efficiency upgrades and code compliance add to the total

For example, an 800 square foot detached ADU at $450 per square foot would cost approximately $360,000 before landscaping or exterior upgrades.

Cost per square foot is helpful for early budgeting, but total project scope ultimately determines the final price.

ADU Cost Breakdown

Understanding how your ADU budget is distributed helps you make informed decisions and avoid unexpected expenses. Breaking down these major line items provides a clearer picture of where your money goes during an ADU project in 2026.

Design, Plans, and Soft Costs

Before construction begins, design and planning expenses typically account for eight to fifteen percent of the total ADU budget. These costs include architectural drawings, structural engineering calculations, energy compliance documentation, and any required site surveys. In some cases, soil testing may also be necessary.

Soft costs also cover project coordination and preconstruction services. Investing properly in this stage ensures the ADU complies with building codes and zoning regulations while minimizing costly revisions later in the process.

Site Work, Foundation, and Utilities

Site preparation costs vary widely depending on property conditions. This phase may involve grading, excavation, and preparing the land for a new foundation. For detached units, a new concrete slab or raised foundation must be constructed. Utility trenching for water, sewer, gas, and electrical lines is also included in this category.

Properties with sloped terrain or limited access may require specialized equipment, increasing labor expenses. In addition, upgrading an electrical panel or connecting to existing utility systems can add to the overall cost.

Framing, Finishes, and Interior Fit-Out

This portion represents the largest share of ADU construction expenses and often accounts for more than half of the total budget. It includes structural framing, roofing, insulation, windows, exterior siding, and drywall installation. Interior components such as flooring, cabinetry, countertops, plumbing fixtures, and paint are also included.

The quality of materials selected directly affects pricing. Standard finishes help control the budget, while custom cabinetry, premium flooring, and designer fixtures significantly increase the final investment.

Permits, Impact Fees, and Inspections

Permits and related government fees are an essential part of ADU construction in San Diego. Homeowners should expect costs associated with plan reviews, building permits, inspections, and utility connection approvals. Larger ADUs may also require school impact fees depending on size and location.

Although these expenses add to the upfront investment, they ensure the unit meets safety, structural, and energy efficiency standards. Proper permitting protects long term property value and prevents legal complications in the future.

Key Factors That Drive ADU Costs in 2026

ADU costs in 2026 mainly depend on size, type, and site conditions. Detached units cost more because they require new foundations and full utility connections, while garage conversions and JADUs are typically more affordable. Lot conditions such as slope, soil quality, and access for construction equipment can increase site preparation expenses.

Material selection also plays a major role. Standard finishes help control the budget, while custom layouts and premium materials increase total cost. Labor rates and energy efficiency requirements in San Diego further influence final pricing.

Permits, Fees & Policy for ADU in 2026

Permit and compliance costs are a required part of building an ADU in 2026. Homeowners must budget for building permits, plan review fees, inspections, and utility connection charges. Larger ADUs may also trigger impact fees depending on local regulations.

Approval timelines can affect overall project costs, especially if revisions are required. Staying updated on local ADU policies and submitting complete plans early helps avoid delays and additional expenses.

How to Budget & Finance an ADU in 2026

A realistic ADU budget should include design costs, construction, permits, utilities, and a contingency reserve of at least 10 to 15 percent. Many homeowners finance ADUs using home equity loans, construction loans, or refinancing options.

Choosing the right financing depends on available equity, interest rates, and long term financial goals. Planning carefully and securing financing before construction begins ensures smoother execution and fewer interruptions.

Conclusion

ADU construction costs in 2026 vary based on size, type, materials, and local requirements. Clear budgeting, understanding permit fees, and planning for site conditions are essential for staying on track. With the right preparation, an ADU can be a strong long term investment that adds both income potential and property value.

Frequently Asked Questions