ADU Cost in San Diego: A Complete Guide to Budgeting Your ADU

How Much Does it Cost to Build an ADU in San Diego?

The average cost to build an ADU in San Diego County varies greatly. Without knowing any further details about an ADU build, we tell homeowners it can range from $200,000 to over $400,000.

Factors like size, location, and finishing costs all come into play. Larger units with high-end finishes have a higher all-in cost than smaller units with more reasonably priced finishes.

The type of ADU you are building also matters. Attached and detached ADUs are new construction, which involves more materials and more labor. Garage conversions, on the other hand, already have the existing structure in place, which can really help reduce costs.

An experienced ADU builder can help keep an ADU project within budget by helping you determine which high-end finishes are necessary and which can be swapped for a more cost-effective option. They can also assess the existing structures on your property, including your single-family home and any garage spaces, to suggest if a basement or garage conversion is possible.

The cost to build an ADU in San Diego ranges widely, depending on the size, type, and features of the unit.

Key Factors That Influence ADU Costs in San Diego

The lot itself, whether or not utilities are present or need upgrades, and choices made during the design phase are key factors in determining ADU costs. This includes the overall square footage and the type of structure, as well as type and quality of finishes. To get a more accurate estimate, you’ll want to understand the costs associated with each construction phase and how the details of your project might impact these costs.

Utility Connections

When thinking about utilities (plumbing, electrical, water, and sewage), there’s the cost of wiring or plumbing the accessory unit itself as well as connecting these utilities to the city power grid or sewage system. These are two different costs. Depending on your site and where these connections need to be made, costs to simply connect these utilities can be as much as $20,000 or even $30,000. If you live in an area where septic tanks are required, those costs could be significant.

What’s more, connecting the city utilities can also involve digging up the existing yard or even a patio space in order to run the connections. If that’s the case, homeowners will need to consider the cost associated with repairing this damage (such as landscaping and masonry).

Utility connections for ADUs, including plumbing and electrical work, can add significant costs depending on the distance from the main house.

Design and Planning Fees

The design phase comes before the permitting phase, and the cost varies depending on whether you’re choosing to submit custom plans or pre-approved plans.

Custom plans often involve the most cost, as they include the cost of architectural design and any necessary surveys. This can amount to $7500 or more. For many homeowners, though, this additional cost is worth it, as it allows them to get an ADU that meets their exact needs.

Pre-approved building plans, on the other hand, are generic plans that meet all the city’s building regulations. These architectural plans are much less expensive because they do not involve the cost of an architect. Some are even free. Pre-approved plans can also reduce the back-and-forth in the permitting process, lessening overall costs for that stage.

Investing in custom design and planning ensures your ADU meets your exact needs while complying with local regulations.

Permit Fees

For any construction project, you’ll need to obtain a building permit from the city before getting started. This requires that a homeowner submit plans (either custom or pre-approved) that meet the city’s zoning laws, as well as paying a building permit fee. These permitting fees vary depending on your city and the details of your build, but we tell most homeowners to assume at least $5000 for permitting, though with larger ADUs, permitting can be as high as $15,000.

That’s because SB13 waives the impact and development fees associated with units under 750 square feet, whereas for larger ADUs, these fees are capped but not waived. To read more about what to expect from your permitting fees, read our blog post about it here.

Construction Costs

Construction costs are where the bulk of the construction budget will be spent and also have the widest price range (between $150,000 and $300,000).
Again, these depend on a variety of factors. The first is labor costs. This can account for as much as 50% of the project’s total budget, so if you live in an area with higher labor costs, this will have an impact on your overall budget.

The next area to consider when it comes to construction costs is site preparation and foundation work. If a lot of site prep needs to be done to lay the foundation, such as the removal of trees, demolition of existing structures, or leveling the lot, this adds to your budget. Moreover, if your architect determines that you need to employ a hybrid foundation as opposed to a standard concrete slab, this also increases your total costs for foundation work.

The final area to consider when it comes to your building costs are your finishes and the cost of materials. While every homeowner wants their ADU to look high-end, this can often be achieved without using only high-end materials, especially when you use an experienced ADU contractor.

Construction costs make up the bulk of an ADU budget, with site preparation, labor, and material choices being key cost drivers.

Types of ADUs and Their Cost Differences

We mentioned earlier that the type of ADU you choose to build and the construction methods associated with each can greatly impact your construction budget, with detached ADUs being the most expensive and garage conversions being the least – still, there are some nuanced differences worth knowing about.

Detached ADU

Detached ADUs are those that are completely separate from the primary property. This means they require their own site prep, foundation, and all the material and labor costs necessary to build the exterior structure. For this reason, most standalone units, even units as small as 500 square feet, can cost upwards of $300,000 to build.

Attached ADU

Attached ADUs are integrated into the existing home but still provide the privacy of a separate living space because they have a separate entrance. They are also a great option for homeowners with a more realistic budget or who lack the property space for a detached ADU. Generally, attached ADU costs are below $300,000 but can be as little as $200,000.

Garage Conversions

Converting an existing garage into an ADU or a junior ADU is generally the most affordable way to create additional space. This is because the foundation has already been poured, and the exterior structure has already been built. The exception is if you plan on building a 2-story ADU or carriage house, as some additional foundational work may need to be done to ensure the structure can support the weight of a second story.

Single-story garage conversions typically cost most homeowners we work with between $150,000 and $200,000 to build, and when they are finished, they can be just as viable as a rental property or granny flat as a standard detached ADU.

ADU Price per Square Foot in San Diego

Rather than trying to guess the cost of each individual phase of construction, you can calculate the estimated costs for your project using the average price per square foot in San Diego. Larger ADUs may cost more overall, but as you will see, they offer better cost efficiency per square foot.

For a 1-bedroom, 1-bathroom ADU that is 500 square feet or less, estimate $600 per square foot. This is your all-in cost, meaning it includes the cost of initial construction and finishing work.

For a 2-bedroom, 1-bathroom ADU that’s 750 square feet or less, estimate $465 per square foot.

For a 2-bedroom, 2-bathroom ADU that’s 1000 square feet or less, estimate $425 per square foot.

Finally, for a 3-bedroom, 2-bathroom ADU that maxes out the ADU size limit at 1200 square feet, estimate $375 per square foot.

Of course, these square footage estimates are based on the average costs in the area and may vary slightly based on your exact location. But when you run the math, you will see that the typical all-in cost ranges from $300,000 to $450,000, depending on the number of bedrooms and bathrooms, as well as the total square footage.

In San Diego, ADU costs vary by size and type, with the price per square foot decreasing as the unit size increases.

Hidden Costs to Consider When Budgeting for an ADU

While permitting costs and labor costs are generally top-of-mind for homeowners, other costs, like landscaping, site prep, and finishing costs, often catch them by surprise.

Landscaping & Site Prep

If extensive leveling work needs to be done to accommodate an ADU on your property, this can come with a significant price tag, as can final landscaping costs. In some cases, this can be $10,000 or more, depending on the nature of the site prep and the final landscaping designs.

Landscaping and site preparation can add to the total ADU budget, but they play a crucial role in integrating the unit seamlessly into your property.

Finish Materials and Upgrades

Higher-quality finishes and custom design upgrades can add significant cost to the final phases of construction. If budget is a top concern, be honest with yourself about what finishes or design elements really matter to you and which you can do without or at least put off until a later date.

Choosing high-quality finishes for your ADU can elevate its aesthetic and functionality, but it’s important to prioritize upgrades that fit your budget.

Breakdown of the Average Cost of an ADU in San Diego

Here is a breakdown of all the construction costs we have mentioned thus far, from permitting fees to utility connections, giving an average cost range for each.

Is Building an ADU in San Diego Worth the Cost?

While there can be a bit of sticker shock when it comes to ADU builds, most homeowners discover these project costs are more than worth it when you weigh them against the benefits.

The first benefit for many homeowners is an improvement in day-to-day lifestyle. If using the ADU as an in-law suite or a place to house adult children, you’ll enjoy the benefits of multi-generational living. If using the ADU as a rental property, you’ll enjoy the additional monthly income from rent. Many times, this rent allows you to break even monthly in paying off the construction loan, and to eventually turn a profit once the loan is paid off.

While a finished ADU can improve your life in the short term, it can also improve your long-term ROI, leading to a significant increase in your overall property value – one that far outweighs any increase in property taxes.

Investing in an ADU not only enhances your living space but also boosts property value and offers rental income opportunities.