Backyard ADU Prices in San Diego County: Factory-Built

10/13/2026

If you own a home in San Diego County and you're thinking about a backyard unit for a parent who needs to be closer, or a grown child who can't make the rent math work, the first question is almost always the same: what does it actually cost? This post walks through the factory-built ADU prices Instant Living posts on its website, what the company says it handles for you, and the basic permit rules from the County of San Diego and the City of San Diego, so you can start the conversation with real numbers.

Instant Living's posted ADU prices

Instant Living, a San Diego-area company that sells factory-built homes and ADUs, publishes a price list for its ADU models. Here is what the site lists today:

• 426 sq ft, 1 bedroom: $89,458
• 430 sq ft, 1 bedroom (studio): $95,548
• 500 sq ft, 2 bedrooms / 1 bath: $105,998
• 780 sq ft, 2 bedrooms: $129,848
• 800 sq ft, 2 bedrooms / 2 baths: $129,998
• 1,041 sq ft, 3 bedrooms / 2 baths: $159,458

A quick bit of math helps when you compare. The smallest unit works out to roughly $210 per square foot, while the 1,041 sq ft model comes in around $153 per square foot. That pattern is normal: kitchens, bathrooms and utility hookups cost about the same whether the unit is small or large, so bigger floor plans usually spread those costs over more space.

Instant Living also says its home and ADU models are available at "less than 35% of the cost of traditional construction." That is the company's own claim. If you are comparing against a site-built ADU, ask for an itemized quote on both so you can see the difference for your specific lot.

What Instant Living says it handles

One of the hardest parts of an ADU project is coordinating everyone involved. Instant Living says it has the professionals to include everything in a project: permit processing, the home itself, the foundation, utilities, appliances and inspection. The company also offers a free site assessment and helps with design, site work and installation.

Every backyard is different. Slope, access for delivery, distance to the sewer and electrical service, and whether you need a utility upgrade can all change the final number. When you get your quote, ask the team to confirm exactly which of those items are included in the price for your property, and which depend on what the site assessment finds.

Why families are choosing backyard ADUs

Instant Living calls itself a family-first company, and its focus is on keeping families together. A backyard ADU can give an aging parent their own front door, kitchen and bathroom just steps from the main house, so help is close by without anyone giving up privacy. The same setup works for an adult child who is saving for a home of their own, or for a caregiver who needs to be nearby.

For a single parent or a couple, the 426 sq ft one-bedroom or the 430 sq ft studio-style unit may be all they need. If a grown child has a partner or kids, the 500 sq ft two-bedroom or the 800 sq ft plan with two baths gives everyone more room. The 1,041 sq ft three-bedroom is closer to a small house.

ADU basics in San Diego County

California's housing department, HCD, describes ADUs as one way to increase the supply of affordable housing, and notes they go by many names, including granny flats and in-law units. Its Accessory Dwelling Units page links to the state ADU Handbook.

Which local rules apply depends on where your property is.

Unincorporated San Diego County. According to the County of San Diego's ADU page, your property must be zoned residential and have an existing or planned main house, and you need a building permit. A detached ADU can be up to 1,200 square feet regardless of the main house's size. An attached ADU can be up to 50% of the main house's area, capped at 1,200 square feet. The County's trial impact fee waiver ended on January 9, 2024, so plan for permit fees in your budget.

City of San Diego. The City's Information Bulletin 400 says a building permit is required for every ADU, with no exemptions, and that the maximum size for an attached or detached ADU is 1,200 square feet. The property owner is not required to live on site for an ADU. ADUs in the City are subject to development impact fees, and properties in the Coastal Overlay Zone may also need a Coastal Development Permit.

Every one of Instant Living's posted ADU models, up to the 1,041 sq ft three-bedroom, falls under that 1,200 sq ft size cap. Other cities in the county have their own rules, so check with your city's planning department or ask Instant Living to look into it during your site assessment.

Questions to ask before you sign

Bring a few questions to your first conversation. Which items in my quote are fixed, and which depend on my site? Will I need a utility or electrical service upgrade? What permit and impact fees should I expect from my city or the County? And how long do permitting, delivery and installation usually take for a lot like mine? Clear answers to those four questions will tell you far more than a price per square foot.

Get a price for your backyard

Instant Living serves homeowners across San Diego County, as well as Temecula, El Centro and Orange County. You can start your project online, browse one of the most-viewed homes on the site, the BD 83, learn more about Instant Living, or contact the team to book a free site assessment. Prefer to talk it through? Call 858-205-8014.