How Much Does It Cost to Build an ADU in San Diego

By Cali Dream Construction, CSLB #1054602, a licensed San Diego general contractor. Call (858) 434-7166.

An ADU is a complete small home on your property: foundation, framing, plumbing, electrical, kitchen, bathroom. That is why it costs more than a room remodel and less than buying another house. Here is what the numbers look like in San Diego, and what moves them.

Can I build an ADU on my property

In most cases, yes. California state law lets single family homeowners add a detached ADU, a garage conversion, or a junior ADU, and cities have to permit it. California allows up to 1,200 square feet on most single family lots, with local rules sometimes shaping the final number. Your lot size, setbacks, and your specific city's rules decide what fits. Call (858) 434-7166 and we will look at your lot and tell you what is realistic.

What do ADUs usually cost by type

Published 2026 California ADU cost guides break it down by type:

Junior ADU. A conversion inside your existing home, up to 500 square feet. Industry guides place these lowest because the shell already exists.

Garage conversion. 300 to 600 square feet. One 2026 guide places California garage conversions at $150,000 to $250,000, while another places them at $100,000 to $175,000. The spread reflects how much structural, insulation, plumbing, and electrical work your garage needs.

Detached ADU. 500 to 1,200 square feet, built from the ground up in the backyard. One 2026 guide places detached ADUs at $225,000 to $400,000 plus; another at $200,000 to $400,000 plus. Detached units carry the full cost of foundation, framing, roof, and utility connections.

Prefab or modular. 400 to 800 square feet. Guides place these at $100,000 to $250,000, noting they can run 15 to 30 percent cheaper per square foot than site built, with faster timelines but the same permit and utility costs.

Overall, published guides put typical California ADU projects at $150,000 to $400,000 plus, with per square foot figures around $250 to $600 plus in higher cost Southern California markets. Statewide homeowner research cited by a San Diego ADU builder puts the median construction cost at $150,000, or about $250 per square foot.

These are published industry figures, not quotes. San Diego sits toward the upper end of every range because of labor rates, permitting, and site work.

A real local number, labeled honestly

Earlier this year we prepared a preliminary proposal in Escondido to convert two detached garage bays into two studio ADUs of about 400 square feet each, proposed at $96,500. That was a proposal, not a completed build, and it used existing structures, which is why it sits far below ground up detached construction. We include it because it is real, from our own desk, not a number we borrowed from the internet.

What drives the price up in San Diego

Type and size. A ground up detached two bed two bath costs far more than a garage conversion. Note the per square foot trap: a full kitchen and bathroom cost roughly the same in a 400 square foot ADU as in an 800 square foot one, so smaller ADUs look more expensive per square foot. Budget on total project cost, not per square foot alone.

Site and utility connections. Slope, access, distance to the sewer lateral, and panel capacity move the number. Trenching, utility upgrades, and retaining are pure site cost.

Soft costs. Design, engineering, surveys, energy compliance, and permit fees run 10 to 20 percent of the budget in published breakdowns. In San Diego, the permit path is the part most homeowners underestimate.

Finishes. Standard finishes versus custom tile, stone, and designer fixtures. An ADU rented long term does not need luxury finishes; an ADU housing family might deserve nicer ones. We quote both.

Coastal and HOA review. Coastal zone review and HOA architectural review add time and cost in many San Diego neighborhoods. Factor review timelines into your schedule, not just your budget.

How to think about payback

San Diego ADU builders note that most ADUs pay for themselves within 5 to 15 years through rental income and property value, with faster payback in high demand markets like San Diego. Homes with ADUs sell for meaningfully more than comparable homes without them. The honest math: total project cost, realistic rent for your neighborhood, and your hold timeline. We will walk through it with you before you commit.

What happens next

ADUs are ground up construction, so you want a licensed general contractor, not a handyman crew. Cali Dream Construction is a licensed general contractor, CSLB #1054602, based in Escondido at 2802 Paseo Del Sol. The process starts with a free site visit and a written quote, then plans and permits through your city, then construction on a schedule we commit to. Call (858) 434-7166 for an exact quote for your lot.

Related Guides

Planning a project? Call Cali Dream Construction at (858) 434-7166, CSLB #1054602, San Diego County.