All ADU Resources

Who Can Build a Detached ADU?

Anyone can build a detached ADU so long as it follows state and local regulations. Discover how using an experienced custom ADU company can help get the best results.

September 3, 2019

ADUs are more popular than ever, but are you actually able to build one yourself? Many people falsely assume that they aren’t able to build a detached ADU on their property that they can use to rent out or house family members.

However, this dream can be made into a reality so long as you understand the requirements and regulations that come along with it.

Detached ADUs vs. Other Types of ADUs?

There are many types of ADUs. There is one to fit almost every lifestyle and aesthetic preference.

A detached ADU is a completely separate structure from the existing home. A detached ADU is a great way to provide a private and unique space to promote an independent lifestyle for adult children, aging parents, renters, etc.

Detached ADUs are the inverse of attached ADUs as the name suggests. These units are built to be attached to the existing home. Although they don’t always provide as much privacy, they allow you to maximize your space by eliminating necessary setbacks between the main house and the ADU unit.

Finally, there are conversion ADUs or “junior” ADUs. These units are essentially built into the existing home structure to become a separate unit—complete with its own bathroom and kitchen space. For instance, basements, attics, or spare bedrooms can be converted into JADUs.

Who Can Build Detached ADUs?

Back in the day, ADUs were quite difficult to build, and few went through with doing so due to local regulations and an opaque construction process. However, recent changes in California state regulations have made it possible and easy for tons of people to be able to build detached ADUs on their properties. This change couldn’t have come at a better time, considering the fact that housing costs in the state are rising exponentially.

The California Statewide Exemption ADU regulation sets requirements for detached ADUs for the entire state. That being said, different localities also have the ability to establish their own set of requirements that may differ from those at the state level.

For more locality-specific information regarding ADUs, click here for areas including Los Altos, Milpitas, Oakland, Palo Alto, Santa Clara, San Jose, and many more cities across the Bay Area and beyond.

Where Can You Build Detached ADUs?

Despite looser detached ADU restrictions in California as of early 2021 compared to other states, there are still rules in place that determine where you can build these structures.

For starters, there are setback requirements that generally state that your newly constructed detached ADU needs to have at least a four-foot setback from the edge of the unit and your property line.

However, for existing structures like garages or sheds that are being converted into detached ADUs, the regulations differ. So long as the structure is legal and permitted, you do not have to worry about it being within that four-foot setback.

Additionally, there are setback requirements that state that your newly constructed detached ADU needs to be a certain distance away from the existing home. The exact distance of these setbacks varies by locality but generally ranges from six to ten feet.

How Big Can You Build a Detached ADU?

When you’re building a detached ADU from scratch, it’s tempting to go as big as possible to truly maximize your space. However, there may be size and height restrictions that you need to take into account before finalizing your plans.

For instance, the California Statewide Exemption ADU regulation requires that the structure must be below 800 square feet in size and below 16 feet in height.

But before you get discouraged about being limited to just 800 square feet for your detached ADU, there are local regulations to take into account. Many localities allow for larger structures that are often based on lot size and coverage.

In Northern California, regulations in San Jose allow for detached ADUs of up to 1,000 square feet on lots less than 9,000 square feet in size and detached ADUs of up to 1,200 square feet on lots larger than 9,000 square feet.

Additionally, San Jose has implemented looser detached ADU restrictions in terms of height. The city allows one-story ADUs to reach up to 18 feet tall and two-story ADUs to reach up to 24 feet tall.

Digging through and interpreting all of these different regulations can be confusing and overwhelming—which is where ADU experts like Cottage can lend our experience and expertise. Feel free to reach out to us about any location-specific questions so that we can tell you exactly what type of detached ADU you’re able to build on your property.

Can You Build More Than One ADU?

Before you start building multiple detached ADUs on your property to maximize your space and income, you should again look at state and local regulations. At the state level, single-family homeowners are allowed to have a single detached ADU alongside a junior ADU.

So even though you may not be able to build more than one detached ADU, you still have the potential to get creative with other options—for instance: an attached garage.

Multi-family homeowners are allowed to have two detached ADUs on the property. The best and most cost-efficient way to do this is to create an ADU duplex of sorts that consists of two separate units with a shared wall. This allows you to maximize the space with two units while saving on construction costs.

While these types of structures are allowed per state regulations, you will also need to consult local regulations as well that may be more strict in terms of how many ADUs you can have on your property.

Should You Convert or Build From Scratch?

There are two different options when it comes to building a detached ADU: converting an existing structure into a functional unit or building completely from scratch.

If you have an existing structure like a garage or shed, oftentimes, it makes financial sense to convert said structure into your detached ADU so long as it provides you with the space and features you’re looking for and the structure is sound enough to convert in the first place.

On the other hand, if you don’t have any existing structures to work with, it’s definitely possible to build a detached ADU completely from scratch with its own foundation, utility connections, etc. While this option may cost you more, it also gives you more freedom in terms of design and construction since you’re not working with a set footprint.

How To Design the Best Detached ADU

Based on everything you now know about detached ADUs, designing and constructing them is anything but straightforward. So how can you achieve an ideal result that works for your space and needs? The best way to do this is to work with a specialized ADU company that knows these regulations and the general ADU process. They can guide you through each step in the process from feasibility to design, permitting, and finally, construction.

How To Choose the Right ADU Designer and Builder?

However, choosing a specialized ADU company is easier said than done. There are so many different options out there that it can be hard to make a decision. At the end of the day, you want a company that gives you the best bang for your buck with the least amount of hassle.

Cottage is a custom ADU company that offers all of that and more with our ADU services. Our process includes everything from start to finish, and we work with vetted contractors to ensure that you get the amazing results that you’re looking for.

Look for the Next Steps

To take the next step in building your dream detached ADU, reach out to the experts at Cottage today for a free consultation and estimate.


  1. First Ever Statewide ADU Owner Survey Shows Growth, Room for Improvement | Berkeley Terner Center
  2. ADU Handbook | California Department of Housing
  3. Accessory Dwelling Units (ADUs) | City of San Jose