A garage apartment is a conversion of an existing garage into an accessory dwelling unit (ADU), or dwelling space within a main property. It is among the most popular types of conversions, because it can be done entirely within the existing main building, often inexpensively and relatively fast.
That said, garage conversions aren't always quick and cheap. They can be extensive and expensive, ultimately increasing the living space of a home enough for an entire additional family to move in. Not all homes have this potential -- nor do all homeowners want that much of an extension. So when you see the term "garage apartment" in a listing, or are considering it as a home improvement, don't assume a certain square footage or style.
Two types of garage apartment
One defining factor in garage conversions is how much space is available: one story or two.
One-story garage conversions
If you're really just talking about the space inside a one-car one-story garage, the conversion is going to be the size of the garage: a one-room bedroom or a studio. It may not have direct access to a bathroom without going through the main house. These types of garage conversions are typically used to house immediate family members of the main occupants, because the occupant will have to go into the main house for everything.
Some people do look to rent this type of garage conversion because it's cost-effective and they either don't need regular access to the rest of the house or feel they can make do with what the garage apartment offers as is. Rent-wise, it's sort of one step removed from renting a room, offering just a bit more privacy and its own entrance for about the same cost.
Two-story garage conversions
A freestanding garage, or a garage with a storage unit on the second floor above the garage, can be converted to a two-story garage unit that's like a full apartment or "tiny house" adjacent to the main house. To be a true garage apartment, this would have to be self-contained, meaning with water and plumbing and some sort of kitchenette at minimum.
This type of unit can rent at the cost of a self-contained apartment rather than a room, and thus many people first consider doing the conversion to create an income property, not just for more space.
However, the increasing popularity of multigenerational housing means that even as short-term rentals are losing viability, more homeowners are looking into garage apartments with a different intention. Instead of a revenue stream, they're looking to create a semi-private dwelling for adult family members.
Costs to do a garage conversion
The costs to do a garage conversion have a wider range than most types of ADUs because the potential square footage varies so widely. A simple one-room garage or carport conversion can start at just $6,000 to $10,000 and go as high as $20,000. A two-story garage apartment starts at around $40,000 and can cost more than $100,000, especially with multiple bedrooms.
What's legally required for a garage apartment?
Legal requirements vary according to municipality and county, but in general there are several requirements for a garage apartment over and above a basic garage. These may include minimum ceiling height, placement of electrical outlets, fire safety, and temperature stability.
Even though this project takes place inside the existing four walls of a room in your home, cities don't generally take the position that you are free and clear to do what you want with your space. Different permits, including electrical, need to be issued for different parts of the project. The more extensive the project, the more involved this process will be. You may even need an architect to draw up plans. If you don't take care of all the steps, then your project will not be up to code.
Once permits are pulled and the work begins, you need to make sure it's done to code, because after each step is completed, a city inspector needs to approve it. The town keeps records of this on file, and if you get the permits but don't get the inspections, the project will come up as unfinished if anyone looks at your home's records. This can cause big problems should you try to sell.
Minimum comforts as specified by building codes
A garage is typically a large box with a cement floor and lighting. It may seem close to livable, but in reality you'll need to add other flooring and fixtures, plus insulation to regulate temperature and wall outlets for electrical needs. Additionally, the ceiling needs to be a minimum height from the floor. Some things, like installing windows in existing walls, can be quite complicated and require a licensed contractor.
If you're looking to create a fully self-contained unit, there will also need to be consideration for heating and air conditioning, plumbing/bathroom, kitchen, and windows.
Provisions for alternate parking
The city, in many cases, needs to be convinced that there's a viable parking alternative for the cars that belong to owners who are converting their garage. What many people don't realize is that allocating parking space per dwelling is a zoning issue. It's not enough for a homeowner to just decide they can find street parking around the block.
Red flags to look for
If a converted garage apartment doesn't have windows or a conventional door to the outside, isn't retrofitted with heating, or has only one or two electrical outlets, then it may not have been done to code. Also, if the electrical, decor, or plumbing work seems to have been DIYed, it may have been done unpermitted. The problem with this isn't just that the space might not be too comfortable; it might be unsafe.
Pros and Cons of adding a garage apartment
There's no set list that pertains to every person considering this type of home addition. However, here are some general pros and cons: