The Cost of a Garage Conversion vs. Building An ADU

Posted On July  24, 2023

Are you curious about adding square footage and value to your property through either a garage conversion or a detached ADU? If you’re considering taking the plunge with either a garage conversion or a new ADU, we can help. We’ll walk you through everything you need to consider when making this decision for your home and your family, including square footage needs, garage conversion cost, land use, and more.

Garage converted to an ADU

Garage Conversions

How do you know if a garage conversion fits your needs? Consider these important points when thinking about your project:

Simplified Permitting Requirements

While this can vary depending on your municipality, often there is less bureaucratic legwork around converting an existing structure versus building a new, freestanding structure. This means your project might be subject to planning reviews resulting in a potentially longer and more complicated permitting process. Simplified permitting requirements will help keep your garage conversion cost down and keep your project on a timely schedule.

Garage Conversion Costs are Generally Lower

Your overall cost depends on a lot of factors, including the materials you choose and your specific aims for the conversion, but generally speaking, a garage conversion will cost less than building a new freestanding ADU because some of the structure is already in place. Architects will be able to account for the fact that the foundation, framing, and roofing will not need to be built from scratch. It will also be simpler to tie into existing sewer and power sources.

Standalone ADU with an outdoor couch and the light on

Why A Garage Conversion Could Be Right for You

A garage conversion is a wonderful choice for families who need an in-law suite for a loved one, a private living space for grown children, or a source of rental income. The cost of a garage conversion is lower and less work is required to complete this type of project, as opposed to building a detached ADU. Also, you get to preserve and continue to enjoy your backyard, without converting it to living space.

However, if you depend on your garage for car storage or it’s already being used as a workspace, you might find yourself leaning more towards building a standalone ADU. Read on to learn more about the costs and advantages of going in that direction.


Are you leaning toward building a new ADU? Great! Here are some more factors to consider as you evaluate which choice is best suited for your needs:


A freestanding ADU can feel like a private oasis and offers that “guest house” feel that you may not get with a garage conversion. Set apart from the main house, a detached ADU offers a sense of separation while still existing on the same property. This can be especially important if your goal in building an ADU is to increase your income by using it as a rental property. A stand-alone structure with greater privacy may be more of a draw to many prospective renters 

and allow you to generate more income and offset the cost of building an ADU.

Modern and updated kitchen and living room in an ADU

More Design Freedom

While it can cost less to convert an existing structure like a garage, designing a detached ADU gives you more freedom to create the structure to your specifications. While your design may be impacted by permitting laws and regulations, generally speaking, you’ll have more flexibility in the overall look and feel of a new ADU versus a conversion.

Why Building an ADU Could Be Right For You

If the higher cost of building a new, standalone ADU is within your budget, a detached ADU can be a great choice for property owners looking to add square footage, provide housing for a loved one who is still relatively independent, or create a relaxing retreat space of their own.

Cost of Construction

While there is no clear-cut price and every project will have different estimates based on a myriad of factors. According to an ADU construction pricing calculator developed by the city of Oakland:

  • A new construction ADU with 1 bedroom and a bathroom of up to 600 sf is estimated at around $242,000. (standard level of finishes and no problematic site conditions)
  • Converting an existing garage or pool house into a 1 bedroom and bathroom unit is estimated at around $144,000. (standard level of finishes and no problematic site conditions)

Get Your Project Started

At EZ Plans we simplify the home renovation process through transparency and clear communication. We help homeowners by creating plans for any size renovation project, from garage conversions and ADUs to additions and whole-home remodels, and we also take care of permit approvals and provide contractor recommendations so your project gets off the ground without a hitch. Our architects are fully licensed and insured and will work with you to make your home remodel dreams a reality. We deliver speed, talent, and affordability. Get started with our transparent architectural pricing tool today.