San Diego ADU Cost Guide

1. Typical ADU cost ranges in San Diego

Costs vary depending on size, site conditions, and level of finish, but most permitted ADUs in San Diego fall into these rough ranges:

Ranges above are ballpark estimates and do not replace a project-specific quote.

2. What's included in “all-in” ADU costs?

When you hear a number for an ADU, ask whether it's just the "sticks and bricks" or truly all-in. A realistic San Diego budget usually includes:

• Design & engineering: architectural plans, structural calculations, Title 24 (energy), and any required studies.
• Permits & fees: city or county plan check fees, permit fees, sometimes school or utility fees.
• Site work: grading, foundation work, retaining walls, trenching for utilities, and driveways or walkways.
• Construction: framing, roofing, windows, insulation, drywall, finishes, and fixtures.
• Utilities: sewer or septic connection, water, power, gas, and any panel upgrades.
• Soft costs & contingencies: surveys, reports, financing costs, and a buffer for surprises.

3. Cost by size: small, medium, and large ADUs

Cost per square foot often gets cheaper as you build bigger, but the total project cost still increases. Here's a simple way to think about it:

• Small ADU (under 450 sq ft): often used as a studio or small 1-bed. Higher cost per sq ft because you still pay for a kitchen, bathroom, and all the same utilities.
• Medium ADU (450–750 sq ft): the sweet spot for many San Diego lots. Good balance of livability and cost.
• Large ADU (750–1,200 sq ft): feels more like a small house. More framing, finishes, and site work add up.

Use our ADU cost calculator to plug in your size and get a tailored range.

4. The biggest cost drivers in San Diego

Two ADUs with the same square footage can have very different prices. In San Diego, the biggest cost drivers are:

• Site access & slope: tight lots, hillsides, and limited access for equipment drive up costs.
• Utility distance: long trenching runs for sewer or electrical service add thousands of dollars.
• Level of finish: tile, cabinetry, and fixtures can swing the budget by tens of thousands.
• Prefab vs. custom: prefab can simplify construction and reduce some costs, but site work is still required.
• Garage conversion vs. new build: conversions often reuse structure and utilities, but can be complex if the existing garage is in poor condition.

5. Ways to keep your ADU budget under control

• Start with a clear budget range before you get too deep into design choices.
• Consider proven or pre-engineered plans instead of full custom design.
• Keep the footprint simple (rectangles are cheaper than elaborate shapes).
• Minimize long runs for sewer and electrical when choosing where the ADU sits.
• Lock in a contingency (often 10–15%) for unknowns uncovered during construction.

6. Next steps: get a tailored estimate and talk to builders

Every property and project is different. A small amount of planning up front can save you from expensive surprises later.

1. Use the ADU cost calculator to get a custom range based on your size and level of finish.
2. Browse ADU builders in San Diego to see who works in your area and what they specialize in.
3. When you're ready, use our lead form on the homepage to share a few details and get a curated shortlist of builders.