Should ADUs Have a Formal Foundation?

Published On July 7, 2022 | By Oliver | Home Improvement

When you’re building your first ADU, you have to take a lot of rules and regulations into account, including if you should or shouldn’t have a foundation. A foundation is an incredibly important part of a building, but with a building being so small, is a foundation really needed? We’re going to go over exactly what an ADU is and the types of foundation you may need, along with if you can build an ADU without a foundation at all.

What is an ADU?

An ADU or Accessory Dwelling Unit is a secondary housing unit to your home. Its often used as a starter home or as a remote office to help keep your work and home lives separate. These units are well crafted and often resemble homes with different styles, shapes, and sizes. They can be used for a wide variety of different purposes, including small businesses, personal sanctuaries, homes, and office environments. ADUs are becoming more and more popular and are making life more convenient for plenty of homeowners in the San Jose area.


One of the first potential foundations you can expect is a concrete foundation. This foundation is made as a unified piece by framing out where it will go and filling the frame with concrete and metal supports. Building on a concrete pad can be incredibly convenient as you’ll have a level pace to work with from the point your concrete sets.

Cinderblock and Wood

Building an ADU with cinderblocks and wood is another potential option when you’re trying to build an ADU. Making sure these points are level can be a bit of a difficult task when compared to pouring a pad, but regardless of your choice, the cinderblock and wood board foundation method is another decent one that can be used in the area. Make sure, regardless of the type of foundation you use, that you have insurance on your ADU in case of damage via an earthquake; smaller buildings are easier for earthquakes to move, after all.

No Foundation

No foundation when you’re creating an ADU is not an option. Especially here in California, where there are earthquakes galore, there isn’t a way to build a building, regardless of the size, safely without a foundation. Working without a foundation also will likely not be legal in your area, as many code enforcement officers and county laws require a proper foundation to ensure the safety of those within the building.

Foundations are an essential part of a building process, no matter what size building you’re creating. You won’t be able to get away with working on a building without one. Thankfully at Action ADU, we can build your ADU for you, taking the stress out of the build and which foundation you’ll need. Regardless of the type of foundation you pick or the type of ADU you decide you would like, feel free to reach out to us at Action ADU today so we can help you get your project started!

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About The Author

Oliver Beau Martinez: Oliver, a home security expert, provides recommendations on security systems, safety tips, and ways to make homes more secure.