A granny flat above the garage is private and romantic—perched in the treetops far from the main house. Renters love them!

An above-garage ADU is also the ideal way to add housing while saving the garage itself, with its valuable storage space and secure place to park your vehicles.

While the square footage of this type of ADU is limited by the size of the garage, you can add a balcony for outdoor living. You can also expand the space by cantilevering the upper floor on one side. The stairs and landing can hold flower pots or an herb garden.

Charm? Through the roof!

The Cost of Building Over a Garage

So why doesn’t everyone build their ADU over the garage? It’s the price tag. If a 400- square-foot garage conversion starts at about $120,000, that same unit built on top of a garage could cost $300,000+. Here’s why.

It’s expensive to build a structurally sound second floor with an open expanse below.

Garages are typically 20′ to 24′ square feet. In order to make the space viable for driving vehicles in and out, you can’t have support posts running down the middle. The existing structure must be reinforced around the perimeter.

The floor of the granny flat is also a challenge. It must not flex or bow, which could damage the flooring. Because there are no posts down the middle of the garage to support the floor above, the builder must use several layers of subflooring.

You may need—or want— to match the exterior of the new structure to that of your main house.

When you’re simply converting the garage, you can paint over the existing finish. Not so when you’re adding a second story. Now you’ll need to refinish the exterior of the entire structure.

Many homeowners want to match the exterior of the ADU to that of the main house. In certain cases it’s required, for instance, if your home is in a historic overlay zone. Some jurisdictions may require it as well.

To match the exterior of the main home, you’ll need to find similar siding, shingles, brick, or stone. You may need to find a plasterer who can copy plastering techniques of 50 or 75 years ago. Whatever the finish material, this two-story structure will require a lot of it, which adds to the cost.

granny flat over the garage

If the garage is attached to the main house, the second floor must align.

This typically involves shortening or increasing the height of the existing garage walls so that the new and old floors align correctly. Even if the main house is only one story, the two-story garage/granny flat has to make sense visually, with the second floor aligning where the first floor of the main house ends.

Utilities cost more to install.

Installing plumbing, gas, and electricity to the second floor requires more materials and labor than when it is on the ground floor.

You’ll need a new roof and stairs.

One of the big advantages of doing a garage conversion is that if your garage roof is in good condition, you don’t have to pay for the ceiling structure or roofing. Not true when you’re adding a second-story ADU. And of course you’ll need stairs to get to the second story.

Need help deciding if a granny flat will work on your property? Check your address and see what Maxable can do for your home during an ADU Planning Call.

How Will the Granny Flat Impact the Main House?

The added costs of building an ADU over the garage are well worth it to many of our clients. When meeting with your Maxable designer to brainstorm your over-garage options, think about how the structure will impact life for folks in the main house.

granny flat over garage


The biggest impact of the structure will be its height. The smaller your backyard, the larger the second floor will feel to those in the yard and the main house. Your designer can help you assess how the height will affect the sunlight your yard and home will receive in different seasons.

Roof height and angle can make a big difference. A shed roof, flat roof, or one with a low gable will block less sun than a roof with a high-pitched gable. A good designer will know how to make the roof harmonize with the style of your main residence while keeping its sun-blocking impact low.

Blocking the sun isn’t always a bad thing. In hot climates, the two-story building might provide welcome shade in the summertime. If it’s casting too much shadow on your vegetable garden or otherwise causing concerns, a landscape designer can help you re-think the possibilities of your backyard.


People in the main house and those in the granny flat both want privacy. Folks in the ADU want natural light. There are plenty of ways to achieve both.

In the ADU: clerestory windows, frosted glass, top down/bottom up shades, and thoughtful window placement throughout.

For the main house: landscape design that uses trees, shrubbery, awnings, fencing, and other elements to artfully preserve the privacy of the occupants.

granny flat over the garage


During the design phase you’ll also want to consider where the ADU guests will enter your property and where the stairs will be placed. The safety of those in the ADU and privacy for the main house occupants are two important factors.

If your garage is on an alley, think about outdoor lighting, locked gates, and other security features that will make those in the ADU feel at ease.

Maxable ADU designers will help you plan the perfect over-garage granny flat. It all begins with an ADU Planning Phone Call.

Space Savers in a Second-Floor Granny Flat

ADUs built over the garage are usually studio apartments, even if one side is cantilevered out a few feet. So it’s crucial to hire a designer who knows how to get the most out of a small footprint.

  • Maximize built-in storage: bathroom shelving inset in the walls, closets that extend up to the ceiling.
  • Buy furniture that serves dual purposes: a table that doubles as a desk or food prep surface, a couch that flips into a Murphy bed.
  • Choose appliances designed for small spaces, such as a narrow fridge, small stacked washer/dryer, and drawer-style dishwasher.granny flat over the garage

The advantages of an over-garage ADU will last the lifetime of the property. The units will always be prized by your friends or renters, and you’ll be able to keep your garage. Your backyard can remain the size it is today.

No wonder so many homeowners decide to take the leap and build their dream ADU over the garage!

Plan, hire, and manage your ADU project with Maxable.

At Maxable, we believe that building an ADU should be fun and exciting. You shouldn’t have to be the one to deal with confusing obstacles like permitting snafus or ever-changing regulations. We’ll be by your side every step of the way and connect you to experienced designers and general contractors in your area to make sure your project goes as smoothly as possible.

Leave the headaches to us! Check your address and see what Maxable can do for your home during an ADU Planning Call.