Understanding ADU costs in California

The cost to build an ADU in San Diego depends on the size, layout, and how custom you want it to be. Smaller, pre-designed units are more affordable and quicker to build, while large custom ADUs take more time and budget.

For example, a 400 sq ft studio unit starts around $215,000. On the other hand, a 1,200 sq ft ADU with 4 bedrooms and 2 baths can cost about $350,000 or more. So the final cost really comes down to what kind of ADU you’re trying to create.

Cost of Building Multiple ADUs

The cost of building multiple ADUs is basically the combined total of each unit’s cost. Sounds simple, but it’s hard to tell a number since every ADU can vary a lot in size, layout, and features. For example, building two studios won’t cost the same as building a studio and a 3-bedroom unit. Each one has its own design, permitting, and construction needs that affect the price.

What Is the Total Cost to Build an ADU?

When planning to build an ADU, one of the biggest questions is what the total cost will be. The truth is, there’s no universal answer. ADU cost can vary a lot based on size, ADU design, and the type of construction. A simple studio from a pre-approved plan will cost far less than a fully customized multi-bedroom design. Next, we’ll break down the different types of costs.

ADU Feasibility Study

We can’t speak for other companies, but at OneStop ADU, we offer a free ADU feasibility study to help you get started. We’ll look at your property, zoning, and layout options to see what’s possible. It’s a simple way to explore your options without expensive commitments. 

Construction Drawings

Construction drawings are the detailed plans needed to build your ADU. They include everything from layout and structure to plumbing and electrical. These drawings are required for permits and “guide” the entire build. At OneStop ADU, the cost for construction drawings is already included in your project quote.

Permitting Management

Permitting management means we handle all the paperwork, approvals, and communication with the city so you don’t have to stress about it. This includes zoning checks, plan submissions, and any revisions they ask for. At our company, ADU permit cost is part of your full-service quote – so it’s already covered in the total ADU cost.

Solar System Installation (Included with Pre-Designed Plans)

All of our pre-designed ADU plans come with a solar system already included. That means we’ll take care of installation as part of your project. It meets local energy requirements and helps lower utility bills. The full solar setup is built into your quoted price, so there are no surprises later.

Permit/City Fees

Permit and city fees are separate from construction costs and depend on your location and project size. On average, they start around $10,000 but can be higher based on local requirements. We’ll let you know upfront what to expect. 

Property Reports

Property reports help us understand your lot – things like utility access, zoning, and building restrictions. These reports are essential for planning your ADU. The cost starts at $2,500 and can go up depending on property complexity. 

Basic Site Work

Basic site work prepares your property for construction – things like trenching for utilities, grading the land, and setting up temporary access or facilities. It also includes testing for soil and energy requirements. Our pricing for this starts at $25,000, depending on the lot and access conditions.

Upgraded Finish Materials

Upgraded finish materials are optional. Our standard packages already include quality cabinets, countertops, flooring, and appliances. But if you want to upgrade – the extra cost depends on what you pick. For example, if your upgrade adds up to $10,000, that’s simply added to your total cost to build ADU.

Additional Sitework: TBD

Sometimes, extra sitework is needed depending on your property’s layout or city rules. This might include things like removing old pavement or structures, adding retaining walls, handling drainage issues, or doing extra grading. These aren’t always required, but when they are, we’ll let you know what’s needed and explain the cost based on your specific situation.

Additional Utilities: TBD

In some cases, your project might need extra utility work. This could mean setting up a separate electric meter, meeting certain electrical code rules, or installing solar if required by local guidelines. We’ll also check for sewer or water needs, or figure out septic options when needed.

Additional Vertical Building: TBD

Sometimes extra building costs come up based on your lot or local zoning rules. For example, your project might need a fire-rated wall, a deeper foundation, or other upgrades. You might also need to match your main home’s look with specific siding, roofing, or other exterior finishes. In HOA areas, these kinds of requirements are especially common.

Additional Design: TBD

Sometimes extra design work is needed. This could mean modifying layouts, adding custom features, or adjusting plans to meet HOA or city guidelines. These design updates aren’t always required, but if they are, the cost depends on the complexity and time.

ADU Construction Costs by Floor Plan

We also offer ready-made ADU floor plans if you need something quicker and more affordable. For example, our 400 sq ft studio starts at $215,000, a 600 sq ft one-bedroom/one-bath layout starts at $241,000, and a 749 sq ft two-bedroom/one-bath unit starts at $260,000. Each plan includes smart space use and quality finishes.

Factors Affecting the Cost of Building an ADU

• Size. The overall size of your ADU is one of the biggest cost of ADU drivers. Smaller units like studios or one-bedroom layouts obviously cost less than large custom homes with multiple bedrooms and bathrooms. 
• Location. Where your property is located affects everything from permitting costs to construction access. Sites with tricky terrain, limited access, or unique zoning rules can cause higher prep and approval costs. City-specific requirements and local labor rates can also make prices vary.
• Amenities. The features you choose have a direct impact on ADU cost in San Diego. Even things like solar panels, large decks, or custom bathrooms can quickly raise your budget. 

Why Does It Cost So Much to Build an ADU?

It costs a lot to build an ADU because it’s basically like building a small house, just on the same lot. You still need a foundation, walls, plumbing, electrical, insulation, roofing, appliances – the full setup. Plus, permits, utility hookups, city fees, and inspections all add up.

Custom designs or upgrades (like premium finishes or larger layouts) can increase the total ADU cost in San Diego even more. And since ADUs are usually built in backyards or tight spaces, the logistics can be trickier – which also affects the final price.

How Can You Cut ADU Costs with OneStop ADU?

At OneStop ADU, we focus on keeping things clear, simple, and cost-effective all the way from start to finish. As a trusted ADU company, we offer transparent pricing, competitive build options, and free feasibility studies to help you make decisions without costly commitments.

Are you customizing your layout, picking from our ready-made plans, or want something in-between? We’re here to help you stay on budget without sacrificing on quality. Contact us today to understand ADU price and get started.