One of the best ways to maximize the value of your ADU is to make it as large as building codes allow. In Redwood City, the biggest ADU that you can build is 1200 square feet. However, regulations do not make this easy. You need to fit a lot of criteria in order to get to build an ADU of this size. There are even limitations based on how large your current home is. Here is what you need to know to determine how large your ADU can be.

How to Build the Largest ADU

Each city in California is allowed to generate their own building codes and regulations for ADUs. In Redwood City, building codes require you to meet certain criteria in order to build a full-sized ADU. Here are the most basic size rules:

  • ADUs with only one bedroom cannot be larger than 800 square feet.
  • ADUs with multiple bedrooms may be up to 1,000 square feet.
  • ADUs which meet California requirements for disabled access may be up to 1,200 square feet.

That means if you want to build an ADU at 1,200 square feet it needs to have multiple bedrooms and meet all state requirements for accessibility.

Home and Lot Size Requirements

When building in Redwood City, the size of your home and lot may also impact the size of ADU that you’re allowed to build. Attached accessory dwelling units may not be more than fifty percent of the total living area in the primary dwelling. That means that in order to build the largest possible ADU, your home has to be 2,400 square feet or more. Any less and the size of your ADU will be constricted.

However, note that these rules do not apply to non-attached ADUs which are built in garages or on other portions of your property. This may be a way for you to maximize the size of your build if you own a smaller home.

There are also some requirements that are based on the size of your lot and front yard. For example, you cannot build your ADU if it will shrink your front yard beyond the minimum front yard required in your zoning district. These are often based on stormwater management, so doing so can flood your property!

ADUs also have to follow set back requirements. In Redwood City, your ADU cannot project beyond the front wall line of your main home. It must be set back from the property lines by four feet (this used to be six, but the state government has prohibited requirements beyond four feet.)

There are also rear lot size requirements. So, an ADU cannot cover more than 50 percent of your current backyard. It must also still have a separate entrance from the main home entrance.

Redwood ADU’s Laws are Still Changing

ADU building codes and requirements are set at several levels of government, including national, state, county, and municipal. And they don’t tend to update their rules and requirements at the same time.

If you want to do your own research, one good place to start is’s ADU page

While keeping up with these requirements as a homeowner can be daunting, our team regularly reviews all requirements so we can provide accurate information to potential clients. Feel free to call and speak with our experts any time. 

How Large Can You Build Your ADU?

Before you make plans for your ADU its wise to reach out to an expert and talk about what size ADU you can build on your specific property. Our ADU construction team is always happy to weigh in, so reach out today.