Rightsizing Your ADU Project: Budgeting for Your ADU— Part 3

As small homes, ADUs are a significant investment for the typical homeowner and must be designed to work within an owner’s ability to pay or finance the project. To get an ADU project to provide a maximum value to a family it must be the right size. Not too large or costly and not too small which would reduce its utility and value.

Understanding financial implications of ADU configurations is the foundation of budgeting for your project. When trying to budget for an ADU, a cost per square foot is often used and is mostly a reliable starting point. There is, however, no fixed per square foot number that applies across the board. These numbers vary greatly depending on location, slope of site, site access and other variables. For a flat site with sufficient space for access for small construction equipment (five feet minimum) the following guidelines should be reliable for determining project costs. These costs are “all in” and include design fees, permit fees and construction costs. They do not include landscaping and assume only minor exterior construction such as small concrete stoops at exterior doors. These numbers assume standard economical construction systems and materials for typical ADUs in California

For small studio ADUs of 300sf or smaller, use $700-$800 per square foot. Even if you decide on a prefabricated unit, smaller units have a larger per square foot price tag. A 300sf studio will cost close to somewhere around $210,000-240,000 all in.

For a medium-sized, 500sf ADU, use $600-$700 per sf. A 600sf one-bedroom ADU in California will likely be in the area of $360,000 to $420,000 all in.

For larger two- to three-bedroom ADUs, use $500,000-$600,000 all in. An 800sf two-bedroom ADU will likely be in the area of $400-$480,000 all in.

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