How much does it cost to build an ADU in San Diego?

You’ve probably heard about the COVID-induced building price volatility. Build costs in general have gone up massively over the past year, due to both material and labor shortages, exacerbated by a white-hot housing market. As of this writing in September 2021, we have taken those costs into account for the figures below for ADU costs in San Diego. We want you to be prepared for what the real costs are going to be (vs. leave you in for an unpleasant surprise later). Read more about how we handle pricing at SnapADU.

As a good rule of thumb, figure on $285-390 per square foot for your all-in cost to build a detached ADU, for units ranging from 400-1200 sqft. Roughly 85-90% of those costs are for the vertical building construction. Vertical build cost is the construction cost for the structure itself, e.g. the part of the project that is not dependent on the specifics of your property. To get to the all-in cost, we factor in the costs from design, permitting, sitework, and requirements like solar.

Cost To Build an ADU in San Diego
Type Size Vertical Build Cost Cost per sqft Typical All-In Cost Cost per sqft View Example Plans
1BR/1BA 500 sqft $170K $340 $195K $390 1BR <500 sqft
2BR/1BA 750 sqft $215K $287 $225K $320 2BR <750 sqft
2BR/2BA 1000 sqft $280K $280 $305K+ $305 2BR >750 sqft
3BR/2BA 1200 sqft $320K $266 $345K+ $287 3BR all sizes

Source: Snap ADU (updated September 2021)

All-in costs will be most heavily impacted by site conditions (e.g. grading, utility locations) and local requirements for permitting (e.g. building plan check & permitting fees, school fees). Vertical build costs will be affected by final finishes; our pricing always includes a standard level of finish, including appliances and fixtures. See more about our standard features.


Design & Engineering: $8,000-13,000

A full set of construction drawings along with a site plan will be prepared for your property at a cost of $8,000 for a standard plan. Even with standard plans, the ADU must be situated & adapted to your property specifics. Design also includes Title 24 (required by CA), structural engineering, building code review with the city, permit processing & revisions. The design phase can be more costly if your property requires a survey, but we try to avoid that and advise early on if it is a possibility.

Permits & Fees: $4,000-14,000

A good rule of thumb is $10-12/sqft in fees. While ADUs are now exempt from many fees, there are still several due. No impact fees apply for ADUs under 750 sqft; for ADUs >750sqft, impact fees are proportional to the size of the ADU in relation to the primary residence. School fees are also due, as well as sewer connection fees.

Site Work: $20,000

This number will of course be highly dependent on your specific property conditions. For a level lot, expect typical sitework and foundation to cost $20K. If you need to start moving dirt and putting in retaining walls or a new septic system, sitework costs can quickly escalate – we’re happy to talk about your property to ballpark the sitework cost early in the process for you. These are the biggest cost drivers we help you look out for.

Vertical Building Construction: $130,000-350,000

The vertical building cost is for the structure itself, including all finish materials, like fixtures, cabinets, and quartz countertops. Check out our floor plans for vertical build prices and our home features for a list of everything included in the build.

Solar: $9,000-$14,000

All standalone ADUs are required to have solar in place, unless the primary dwelling already has solar. Basic solar systems cost $9,000 for a 1.44 kw system. Silver lining here is that you’ll save on utility costs!

Other Costs: TBD

While typically not required, you may have additional costs come up if you require additional structural engineering, civil engineering, or soils engineering. You may also need to upsize your utilities, including the water line and electrical panel. We can advise if any of these are relevant for you when we create your proposal.

What is the cost of a Garage Conversion ADU?

A two-car garage conversion ADU in San Diego will typically start at $90-100K, which includes finishes and appliances and a standard 8' ceiling height. These numbers assume the existing structure and building envelope are in good condition. A sloped slab that needs to be leveled can add $3-4K. Any necessary demo & removal of existing walls & ceiling may add on another $3-4K. Sometimes you will uncover issues with the exterior siding, as the conversion is happening from the inside out. A good contractor will work to make you aware of any potential unforeseen costs early in the process to limit surprises.

SnapADU no longer handles garage conversions. However, we are happy to provide you referrals to contractors who handle this kind of project.

When can we talk about my ADU costs?

We want to talk with you about the cost to build an ADU from Day 1 because we think it's vital to align design with your budget constraints. With nearly a decade in construction, we have fine-tuned our process for delivering accurate & realistic construction estimates that we can stand behind. We want to give you a picture of the full costs of the granny flat project, from design & permitting, to site work & construction, plus any extras you should look out for.

Whether you have a sketch or a full set of plans, we can give you a cost to build an ADU so you have the information you need to move forward with your project. The first step is to let us know the address where you want to build and what size ADU you're considering... we'll send you a proposal within 24 hours.

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How do I finance my ADU?

Whether you’re building an ADU for family, securing rental income or creating extra space, making the financing work is essential. Read more about financing options for your ADU project.


Check out our ADU floor plans for cost estimates on each model. We're big on transparency and want you to be prepared with the expected cost for building your ADU. We show all-in ADU costs on a typical job for each design, including costs for all San Diego County Standard ADU Building Plans and the Encinitas PRADU Building Plans. We can put together a proposal for your specific project when you are ready to take the next step.

See ADU Floor Plans & Pricing