Tips for Garage to ADU Conversions

“A lot of people have this notion it’s going to be a slam dunk to convert their garage to an ADU, but there are a lot of considerations for garage conversions. We encourage people to think about whether the structure is worth making use of or whether it’s better to start fresh. I have a hard time saying that because I like old buildings and want to save them. We do a lot of work in the historic districts. But what I come back to is that garages weren’t really built for living, so we have to do a lot to make them comfortable and energy-efficient.” –Jack Barnes, Architect

(Here are three examples of Jack Barnes Architect garage to ADU conversions: Susan Moray’s ADU: Updating History in Ladd’s, Sharon Nielson, Keith Pitt, & Stephanie Mix’s ADU: A Miniature Mansion, Barbara Gundle’s ADU: A 2-Story Garage Conversion.)

Susan Moray’s converted her garage into a guest house Ladd Addition, one of Portland’s historic districts

After basement to ADU conversions, garage to ADU conversions are the second most common way to create additional dwelling space within our existing building stock. Read on to learn about the benefits of garage to ADU conversions, find links to examples of converted garage ADUs, and become familiar with what the deal-breakers are if you’re considering converting a garage into an ADU. (If you’re exploring purchasing a property with ADU potential, be sure to also check out How to Buy or Sell a Property with an ADU (or ADU Potential.))

Why a Converted Garage ADU?

Joe & Naomi transformed their attached garage into an ADU

If the conditions are right, converting your garage into an ADU can be the easiest and most cost-effective way to create an additional dwelling unit on your property. Converted garage ADUs take advantage of existing housing stock, which provides a number of benefits.

Here are some benefits of creating garage ADUs:

• The shell of your ADU may already be built, saving you excavation and construction costs.
• Your garage may have a great deal of charm and it may fit in with the architectural character of your home and neighborhood.
• The materials used to create the shell of your new ADU “back in the day” may not be easy to get your hands on anymore. (“They don’t make ’em like they used to!”)
• There may already be water and power to the ADU. If you have overhead lights and a utility sink, you’re well on your way! Even if they aren’t already where you want them, it may be quicker, easier, and cheaper to tap into these utilities than it would be to pull these utilities to a new detached structure.
• If your garage is attached like Joe Wachunas and Naomi Cole’s ADU or Byan and Jen’s Garage Sweet Home, it may be connected to the house with a single door, making it easy to reintegrate the ADU into the rest of the house if the need ever arises.
• Your garage may already be a “secret ADU” that can be brought up to code and permitted (for instance, your garage may have been used a detached bedroom, a “man cave” or a “she shed” in the past.)
• Converted garage ADUs provide additional housing in desirable, close-in neighborhoods where there aren’t many infill lots. So you may be able to provide your tenant, family member, or yourself with a great dwelling in a place you couldn’t otherwise afford to live.
• You won’t need to give up any additional yard space when you reclaim your garage as an ADU. (Okay, maybe you’ll add exterior storage or a shed. Check out ADU Storage Solutions for more information about how to not obliterate your own storage when you convert your existing storage space into an ADU.
• They provide discrete density on your block without changing neighborhood character. Depending on how it’s done, passersby may not even know it’s a living space!

Real Examples of Garage to ADU Conversions

Jill’s garage ADU helped her have a home of her own

During the ADU Case Studies Project, I interviewed a dozen ADU owners who had converted their garage into a dwelling. (For the purposes of this post, I also included conversions of other accessory structures, too, even if the space had been used to keep chickens or woodworking supplies rather than a car. There are more examples of garage conversions among the ADU Profiles, too!)

Some of the converted garages, like Jill’s Home of Her Own and Isabel Johnson and Brad Creels’ guesthouse, were pretty straightforward projects, accomplished on a modest budget. On the other hand, Susan Moray’s, Barbara Gundle’s, and Sharon Nielson, Keith Pitt & Stephanie Mix’s were high-end renovations of contributing structures in historic districts. A couple of them were conversions of other accessory structures. For instance, Cheryl Levie transformed a chicken coop into a period-appropriate guest house. Meanwhile, Sheila Butler converted a shack on her property into an ADU which she and her family lived in while fixing up the main house.

Jen & Bryan Danger transformed their attached garage into home sweet home

Explore these posts to learn about the challenges they faced and how they persevered. They provide excellent advice about what they would do differently if they had it to do all over again!

Here are a few from the first round of ADU Case Studies:

• Isabel Johnson & Brad Creel’s ADU: A Backyard Guest Room
• Billy Hines’ ADU: Modernizing the Carriage House
• Kathleen Pequeño’s ADU: La Casita & La Casota
• Cheryl & Jim Levie: Recreating a Period Piece
• Don Golden & Edith Casterline’s ADU: A Front Yard Cottage
• Jen & Bryan Danger’s ADU: Garage Sweet Home
• Joe Wachunas & Naomi Cole’s ADU: Reworking the Garage
• Jill’s ADU: A Home of Her Own
• Susan Moray’s ADU: Updating History in Ladd’s

And here are some new ones to be watching for:

• Sharon Nielson, Keith Pitt, & Stephanie Mix’s ADU: A Miniature Mansion
• Barbara Gundle’s ADU: A 2-Story Garage Conversion
• Sheila Butler’s ADU: From Shack to Guesthouse

Top 5 Deal Breakers for Garage to ADU Conversions

There is considerable potential for hidden costs when converting a garage to an ADU. There are many things that can make a garage a less-than-ideal structure to convert into an ADU. Most of them boil down to the simple fact that your garage was constructed to provide a shelter for objects, not people. Here are the top 3 issues you might face:

#1: Structural Challenges

You may find that your “falling down” garage is actually falling down and the structure can’t be transformed into a safe living space.You may also discover that your ADUs footings aren’t sufficient to support the second story that you wanted to add. You may also find that since your ADU is sitting at grade it’s prone to water intrusion (which is, of course, a common complication for Basement to ADU Conversions, too.)

#2: Unpleasant Remnants of Days Gone By

You may find that underneath the siding there’s another layer – of asbestos – siding that will need need to be mitigated. Hopefully you won’t discover, as Satish did, that there is a cesspool located under your garage! (This was also a problem for one of the Hammer & Hand ADUs. Read up to learn how they mitigated it!)

#3: Shared Utilties

You may discover, as Sharon Nielson did, that your property shares a party sewer line with the neighbors. You’ll be faced with the prospect of a major upgrade to your system.

#4: Energy-Efficiency Challenges 

You may also find that your walls are too thin to add even code levels of insulation so you’ll need to fur out the walls just to make the place cozy enough to call home. Additionally, if you retain your concrete slab you’ll find that, since it’s uninsulated, it’s cold all year long.

#5: Design Guidelines

Depending on where you live, you may realize that if you increase the square footage of your ADU you’ll be subject to design guidelines that require your house to match the primary dwelling. (Portland recently changed some regulations regarding ADUs matching when the The Accessory Structures Zoning Code Update Passed.) If you’re in a historic district you may not be able to modify the structure much. You may be required, for instance, to retain at least 2 of the walls and you may not be able to tear the structure down to start over.

Wiping the Slate Clean

Lisa Florentino and Patrick Kernan repurposed parts of their garage into their ADU when they tore it down to make space for the ADU

A few ADU owners decided to get a fresh start, but tearing down their existing garages in order to build an ADU. You can learn about their deliberations and their decisions here:

• Lisa Florentino & Patrick Kernan’s ADU: An Asian-Mexican-Pineapple Chalet
• Satish’s ADU: A Backyard Landlord Cottage
• Steve Snyder & Jackie Ellenz’s ADU: An Energy-Efficient Guest House

An Apartment Over the New Garage

On the other hand, some folks found that for them the best of both worlds was to build a new apartment over a new garage. Jeff McCaffrey & Beth Bonness’s ADU: Hawthorne Guesthouse, Lissa & Matt’s ADU: Planning for Our Sons’ Future, Dan Gray’s ADU: A Retreat Above the Garage, Rambo Halpern’s ADU: An New Old-Fashioned Carriage House, and Ray Chirgwin’s ADU: Carlton Street ADU were all new ADUs constructed above new garages. They avoided the challenges of converting an existing structure and they have a spot for storage and/or workspace.

Ray Chirgwin’s ADU has a shop/garage below

If you plan to convert your garage into an ADU, it’s a great idea to add a contingency line to your budget to address some of these unanticipated possibilities. It will also likely be well worth your money to bring in an ADU Professional to evaluate the situation.

Converting your garage into ADU may not be the right choice for you and your situation. Then again, your best ADU potential may be just a few feet away! Good luck!

About linamenard

Hi. My name is Lina Menard and I'm a small house dweller, designer, blogger, and builder. I'm currently collecting ADU Case Studies for AccessoryDwellings.org. Through my company Niche Consulting LLC, I help people design and build the home (and life) of their dreams! I also tell my stories about simple living in small spaces - like a travel trailer, a yurt, a backyard cottage, and tiny houses on wheels - at Niche News.

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