How to Build a Mother-in-Law Suite in Your Garage

There’s no question that housing options these days are both expensive and hard to find. For those of us lucky enough to have a garage, it can be tempting to imagine building a mother-in-law suite for aging parents, a son or daughter trying to start a career, or even a tenant paying market-value rent. The need is great, and the idea of keeping family members close by can be quite tempting – especially for those looking to minimize childcare costs by asking Mom and Dad to babysit.

If you’re researching mother-in-law suite ideas, you’ve likely already realized the value of adding an “accessory dwelling unit” (ADU) to your property – and might even be getting ready to start pulling together garage apartment plans. It’s a smart move: according to Realtor Magazine, homes with ADUs can be priced up to 35% higher than those without. That’s a lot of value for the effort, not to mention the flexibility of having additional space at your disposal. At CubeSmart, we’re definitely all in favor of that!

Keep scrolling for our guide to building a mother-in-law suite in your garage.

What is a Mother-In-Law Suite?

According to Freddie Mac, a mother-in-law suite or ADU is “a smaller, independent residential structure on the same lot as a single-family home.” To be officially classified as an ADU, the unit needs a kitchen, bathroom, and separate entrance.

While regulations vary from state to state, it’s important to note that some – but not all – areas prohibit building a mother-in-law suite atop an existing garage. Why? Stability. Typically, building code requires a concrete foundation for dwellings while garages are most often built on concrete slab. That’s not to say you can’t tear down a garage and rebuild it with a mother-in-law suite on the second floor, but you will definitely need to add demolition costs to your budget.  

Now that you know how a mother-in-law suite is defined. it’s time to get down to the nitty gritty of planning one out.

How to Plan a Mother-In-Law Suite

After a few months (or years – no judgment!) contemplating in-law suite ideas, you’ll probaby be ready to start the planning process. While you can learn a lot by talking to neighbors who’ve gone down the path before you, and reading articles like this one, you will likely need to call in the professionals pretty early in the planning process. Before you take that plunge, however, consider researching the following components as much as possible to prepare yourself to understand (or even question) what the experts tell you.

Assessing Space and Regulations

Many state and local governments publish comprehensive building codes that establish how structures must be built and equipped, including plumbing, ventilation, and heating / air conditioning requirements. Often, these codes can be accessed online, though they can be hard to understand for those of us who’ve never worked in the building trades.

At a minimum, you should be able to understand the space needed to construct a mother-in-law suite on your property – and how big that suite can be in relation to the space you have. In Denver, for instance, ADU size is based on zone lot area (i.e., if your lot is smaller than 6,000 square feet, the ADU cannot be more than 650 square feet). Long story short: Figure out what the specifications are for your neck of the woods before calling contractors.  

Budget Considerations (Average Cost)

Once you know the requirements for your town or city, you can start thinking about the not-so-fun part of building a mother-in-law suite: the cost. According to Angi, the average cost to convert a garage into an ADU is between $20,000 and $60,000. Of course, if you live somewhere that requires a totally new building is constructed, you might end up paying hundreds of thousands of dollars more.

If you don’t have cash on hand, talk to a bank or other lending institution to figure out how to finance the project – and what it will cost you over the lifetime of the loan. While interest rates have jumped, they are showing signs of cooling off in 2024 which might make it the perfect time to start the project.

Designing the Layout

Designing the basic layout is arguably the best part of building a mother-in-law suite! You will certainly need an architect to pull together (and stamp) final garage apartment plans and construction documents, but don’t let that stop you from imagining the perfect layout for you and your family’s needs. There are many free online layout and design tools that can get you started, so have fun with it! Let your inner architect out to play; you might be surprised at the ideas you have around organizing space and, if you put enough thought into it, they’ll likely be taken seriously by the professionals you hire to help.

Garage Apartment Plans

Once you have combed through in-law suite ideas, figured out the regulations and what you can spend, and come up with a rough layout, it’s time to call in the pros to pull together the garage apartment plans and take it to the next step.

Working with an Architect or Designer

First on the call list should be a number of local architects or architectural designers. Scour online review sites and ask your friends and neighbors for recommendations. You can also search for firms on the AIA website, which maintains a comprehensive directory of American architects. Schedule meetings with at least three to get an overview of the process and outline what you would like to see in a proposal. Be sure to ask about fees, timelines, and deliverables, and if they have any specific builders that they like to work with. Forging a partnership between the architect and the builder early in the project can help it run smoother.

Once you’ve chosen an architect, it’s time to hammer out the details. Expect this to be a collaborative process, with some degree of back and forth. A good architect will work with you to make sure your wants and needs are addressed.

Choosing the Right Floor Plan

When it comes to choosing the right floor plan, you’ll likely want to add notes or revisions to the initial draft the architect presents. Think through different features you want the dwelling to have, including:

• Aging in place design, which is particularly useful if you will have elderly people living in the suite
• Sustainability measures, such as energy-efficiency and making use of natural lighting  
• Technology or “smart home” tools and fixtures that can be accessed by both the owner and tenant

A good floor plan will figure out the best use of space in the mother-in-law suite, while incorporating features to make the home useful over the long-term.

Adapting Existing Garage Structures

As mentioned above, you may or may not be able to adapt your garage to become an ADU. Your architect will certainly be able to work within whatever regulatory confines are in place, and can advise if it makes more sense for you to tear down and start fresh or try to repurpose an existing structure.

If you decide to work with what you’ve got, you’ll need to store the contents of your garage somewhere else for the length of the project (and maybe longer). Search for “storage spaces near me” to find your local CubeSmart and take advantage of our easy online booking tool and month-to-month contracts.

Building a mother-in-law suite is a major project that involves a lot of professionals to get done right. But when it is done right, it can be of major benefit to your family and your finances. Prepare yourself as well as you can in advance by collecting in-law suite ideas, documenting “need to haves” and “nice to haves,” and understanding the limitations on what you can build – and what you can afford. With the right info in hand, you’ll be able to smoothly navigate the process and end up with the ADU of your dreams.