Working With SDB On Your Custom Home Project: Idea Books

While adding a floor to your existing garage seems like a convenient solution to increase your property, most homes including yours are (most likely) unable to add an ADU on top of your existing garage. Building an ADU on top of a garage is more than simply “popping the top”, specific foundation and engineering requirements are needed. That is not to say you cannot build a garage with an ADU on top, you will, however, have to tear down your garage to the foundation and rebuild.

Why can’t I use my existing garage for an ADU on top?

As mentioned, most homes are unable to add an ADU on top of an existing garage. This is because of how most garages are originally engineered and built. The main factor in this lack of engineering is the foundation and support the existing garage is on. Nearly all homes will have detached garages built on top of a slab of concrete. Any conditioned living space will require a proper foundation. A foundation will be able to provide the clearance and protection needed to keep utilities and the insides of the structure from the weather. Also, a foundation also makes it so you can build up, meaning actually having a second-floor, where your new garage ADU would be located. A simple concrete slab-on-grade would not be able to do any of those things, much less pass inspection.

You are basically building a brand new tiny home.

Half of the costs will be expected to match the expense of building a brand new garage but then you will also have to pay an average cost-per-square foot that is similar to a home, maybe even more. The new foundation will be considerably more expensive than a garage concrete slab pour. All the utilities will need to be installed and/or connected to existing ones, sewer and water tie-ins are a large endeavor. Also, the utilities will be run up to the second-floor, which will cost more money than a typical installation. 

Should I still build a garage ADU?

Building an ADU is a great option for homeowners who are seeking another dwelling but are put off by the higher real estate costs. Building an ADU will add to their property value and will cost less than buying a new home outright in most cases. If you are confident that:

• Your property is zoned for an ADU
• You have enough square foot to build on
• Your Garage is over-engineered or is ready to be torn down
• Have a budget that reflects the cost of building a new custom home per square foot

Than you are most likely able to build an ADU on top of your garage.

For more answers, always feel free to reach out to Sustainable Design Build about your residential construction needs.