How Much Does It Cost to Build an ADU in California?

With housing more important than ever, backyard cottages and adding in-law suites are on the minds of many homeowners. Many counties in California have adopted encouraging laws to make adding ADUs easier. If you need a dedicated home office, a place for Mom, or additional rental income a backyard home could be the answer. Here are some common questions we get when clients are thinking about adding an ADU.

What Is An ADU?

ADUs, or accessory dwelling units, are secondary homes on a residential property. They are usually compact (like a tiny house or cottage), but they have their own kitchen, living area, bedroom and entrance. Some ADUs are a suite attached to the main house, while many are built as a separate structure. They are becoming very popular in the Bay Area, and most California neighborhoods are now allowing ADUs to be built on residential properties. There’s never been a better time to build an ADU than now!

The Steps to Adding an ADU

Building a backyard living unit is much like building anything else, but on a smaller scale. First, you will need an architect to create plans. Next, you will need to get it permitted by your county. Then, you need to hire a building contractor to complete the work. In a matter of months, you could have an ADU of your own.

Getting an ADU Custom-Designed for Your Needs

If you want your ADU to perfectly match the styles of your existing house, then a custom design might be for you. You can also choose a custom design if you need something unique and you can’t find pre-designed tiny house plans that work for you. Although, many ADU plans have options for cosmetic customization.

The Cost of a Custom Design: Custom design costs can vary depending on the architect, the project size, and complexity of the design. If you want an economic option, it is recommended that you start from a pre-designed plan and have your architect make custom changes to the plan.

Saving Time and Money with Pre-Designed ADU House Plans

Not only does a pre-designed option reduce the amount of time you would spend designing a custom ADU, but it is also  more affordable. A design plan costs about half as much as a custom design. In many cases, you can still have some control over the exterior appearance, although the floor plan will be standard. Drafting Cafe Architect’s ADU Plans offers 2 exterior finish options and 3 interior finish palettes so you can choose your preferred design style.

Getting Your ADU Permitted

Once you have the architectural design in place, you will need a building permit before you can begin construction on your property. Plans are the first step to your ADU. You will still need permit drawings from your architect. Some may include this and others will charge separately. Once your county and city has approved your design, your building contractor can finally break ground on your ADU.

Building Your ADU

The Bay Area is definitely one of the more costly places to build due to older homes and high demand for remodeling. However, if you look at the overall value that a permitted ADU adds to your property it’s worth the investment.

The Cost of Building: While construction costs will depend on the design of the home and the quality of the building materials, the average you can expect is about $100 to $200 per square foot. If you get a 500-sq-ft ADU floor plan, you can expect the construction costs to be roughly $50,000 to $100,000. You’ll want to get a quote from a trusted local builder in order to get a better idea of expected costs.

Because budgeting is a common question we get from potential clients, we offer a free online instant estimate on our website so you can pre-plan your ADU or other remodeling projects.


Get in touch with us. We would love to help you get your project off the ground