All About ADUs

What is an ADU?

ADU stands for Accessory Dwelling Unit — basically, it’s a second, smaller living space added to your main home. You might also hear them called tiny homes, garden suites, granny flats, or basement apartments. There are four main types of ADUs, shown in the image below. First, there’s the detached ADU — a separate building on your property, often called a tiny house. Next is an ADU built above a detached garage. The third type is an attached ADU, which is added onto your existing house. And lastly, there’s the basement ADU, also known as a basement apartment.

https://housingsolutionsnetwork.org/adu/

What are the Benefits?

One of the biggest benefits of having an ADU is the ability to earn rental income from a tenant. On top of that, having a legal apartment can also boost your home’s property value. ADUs play an important role in providing more affordable and flexible housing options in the community. They offer independent living solutions too — for example, maybe you have a child heading off to college or university who could use their own space. One of my clients plans to rent their ADU to their son, who has autism and needs a space of his own while still staying close to family. ADUs can also be used as a granny flat or a private space for a full-time caregiver.

Beyond personal use, ADUs help increase urban density and reduce urban sprawl. Urban sprawl happens when towns and cities grow outward into undeveloped areas like farmland and green spaces. By adding more housing to existing properties, we can increase density without replacing single-family homes with large apartment buildings or townhouses. This approach helps neighbourhoods keep their original character, with ADUs tucked into basements, rear yards, or side yards. Plus, by building on properties that already have things like roads, sewer lines, hydro, and storm drains, we make better use of the infrastructure that’s already in place.

ADU Above a Detached Garage

Let's Get Technical

The Ontario Building Code, along with your city’s Zoning Bylaws, lays out the rules to make sure ADUs are safe and livable. These regulations can vary a little depending on where you live.

To start, there are minimum and maximum limits for the size and height of an ADU. These are based on things like the size of your property, the footprint of any other accessory buildings on your lot, and the size of your existing house. Your lot must meet a minimum size requirement, and you’ll need to follow specific setback rules from the property lines. An ADU must include certain spaces, like a kitchen, bathroom, and laundry facilities. There are minimum square footage requirements for specific rooms or combined spaces, as well as minimum ceiling heights and door sizes.

Safety is a big focus too. Regulations cover the number and type of exits, requirements for egress windows, and fire separation between the ADU and the main house. There are also glazing requirements — basically, rules about how much window area a room needs to let in enough natural light. These requirements depend on the size of the room, what the room is used for, and even the age of the house. For example, new builds usually require more window space than older homes.

Parking is another important piece. Generally, you’ll need to add one extra parking space for the new unit, and it’s usually okay for this to be tandem parking with your existing spaces.

It’s a lot to keep track of, and realistically, most homeowners aren’t expected to know all of these details. That’s why it’s so important to work with a designer who can guide you through the process and make sure everything is done right.

Basement Apartment & ADU Above Detached Garage

Design Tips and Tricks

Now for the fun part — designing your ADU! I love working closely with my clients to collaborate on the design and bring their ideas to life. Because ADUs are smaller living spaces, it’s important to start by thinking about what’s most important to you and how the space will actually be used. We want to focus on optimizing the layout and making every square foot functional.

There are lots of ways to make a small unit feel bigger. Combining rooms to create an open-concept layout or designing a cathedral ceiling can go a long way in making the space feel more open and airy.

Another key consideration is energy efficiency. You want your ADU to generate rental income — not rack up expensive utility bills. It’s smart to invest in higher insulation levels for the walls, floors, roofs, and windows, as well as energy-efficient heating and cooling systems like air-source heat pumps or in-floor radiant heating. Choosing Energy Star-rated appliances and WaterSense-certified plumbing fixtures will also help keep utility costs down.

If you’re building an attached ADU as an addition or a detached ADU in the backyard, you’ll also want to think about the exterior design. Should it complement the style of your existing home, or stand out with a unique contrast? You’ll need to plan how the tenant will use the outdoor space — defining separate areas for privacy and creating a clear path from the driveway or sidewalk to the ADU will help make the unit feel like a true home.

Walkout Basement Apartment

Case Study: Gardens Edge 

To give you a better idea of what’s possible with an ADU, here’s a look at a project I worked on recently. Every ADU is unique, and Gardens Edge perfectly reflects my client’s vision and lifestyle. This ADU is 510-square-foot and is located in the rear yard of my client’s property. With a strong connection to farming and a passion for gardening, my client wanted a design that reflected those values. Together, we developed a modern farmhouse concept featuring earthy tones and natural textures.

She envisioned a cathedral ceiling in the main living spaces and some attic storage toward the back, which naturally led to a classic gable roof design. Since her home sits on a corner lot, we also had to consider how the ADU would look from the side street. To boost curb appeal, we added a charming covered porch — a perfect spot to sit and enjoy a morning coffee.

Inside, the ADU includes one bedroom, one bathroom, and a bright, open-concept kitchen, living, and dining area. There is a beautiful cathedral ceiling, a cozy living room with a stone fireplace as the focal point, and a spacious primary bedroom with thoughtful design touches throughout.

Looking at the floor plan, one of the first considerations was the corner lot layout. The homeowner wanted both a front door facing the side street and a side door leading into the backyard and gardens. The open-concept living area helps the home feel spacious, while down the hall, you’ll find a utility closet, a full bathroom with a stacked washer and dryer, and a primary bedroom that comfortably fits a queen bed along with plenty of closet storage.

Ready to Get Started?

Now that you know a bit more about ADUs, let’s start designing yours!

You can visit our website at habitatdesignco.com to learn more about our process and check out some of our recent projects.

Follow along on Instagram @habitatdesignco_ for more inspiration, updates, and behind-the-scenes looks.

If you’re ready to chat about your ideas or have any questions, feel free to email me directly at cailyn@habitatdesignco.com — I’d love to hear from you.

Thanks so much for reading!