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“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.)
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?
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:
Real Examples of Garage to ADU Conversions
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.
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:
And here are some new ones to be watching for:
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
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:
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.
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!
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Hi, do you address this question somewhere here? What if the garage is on or close to the property line. Can you still convert it to an ADU? What are the requirements to do so (in relation to the property line/setback issues)? Thanks!
In general, the answer is “you’re gonna have to ask your local planning department.” But in my personal case (in Portland, 2006-07), my existing garage was pretty much on the property line and it was okayed because it was an existing structure we were renovating. We weren’t changing the footprint near the property line. Hope that helps! Martin
In Portland, Oregon a homeowner can typically convert a garage to an ADU if it’s on the property line as long as they do not change the footprint of the ADU and they meet other guidelines, including firewalls and the like. More details are available here: https://accessorydwellings.org/2015/12/02/the-accessory-structures-zoning-code-update-passed/
where do i get blueprints for garage adu conversion
Hi Jerry, I think you’ll find that garages are all so different that you can’t just “get blueprints” for a conversion. Practically anything you build has to be customized to the site, and converting an existing garage will definitely be custom. You might want to talk to a few contractors or architects. If they have actual demonstrated experience building a permitted ADU in your city that would be the best. Hope that helps –Martin