Top reasons NOT to do a Garage Conversion ADU

We continually get inquiries from prospective clients looking to convert their existing garages into Accessory Dwelling Units (ADUs). The main reason people give for wanting to go this route is that they think it will save them money with lower construction costs by reusing a structure that already exists. Although, this is a great goal in theory, for almost every inquiry we recommend not going with a conversion but rather demo the garage and build the new ADU from the ground up. There are many reasons for this recommendation.


Working Within Existing Structures is More Work

Garages weren't designed and built for living in, and many are older and need extensive repairs and alterations to make them livable.

In our experience, renovating garages are often difficult and complex. Garages weren't designed and built for living in, and many are older and need extensive repairs and alterations to make them livable. Documenting the existing structure takes time and multiple trips to the site to verify dimensions over the course of the project. Often roofs are in poor condition and need repairs or replacements, there aren’t windows, or if there are they are small and in awkward locations. Existing walls are often not structurally sound and many garages don’t even have proper structural footings. There usually isn’t plumbing hookups and if there are, it still requires cutting through the concrete floor to get the plumbing the correct places for adding kitchens and bathrooms.

All of these, and other potential complications, means it is more work for the design team as we document the existing space and try to design a new dwelling unit within these limitations. It is more work for the contractors because they have to work around what is there and are limited in what equipment and construction methods they can use. There is more work that needs to be done by hand, and there is more unique measurements and one-off pieces that makes construction longer and more expensive.

As one example, we recently designed an ADU Garage Conversion for a home in the Irvington neighborhood here in Portland, Oregon. As we analyzed the existing structure we found that there wasn’t adequate footings under the exterior walls of the garage. The only way to add footings without compromising the structure, was to dig out 4-foot sections under the existing walls by hand, pouring a new concrete foundation, and then moving on to dig out the next 4-foot section. This is labor intensive work that takes a lot of time. This alone added around $12,000 in construction costs.

That is one example of the additional work and associated cost. On top of that, there is more design time needed for architectural and structural engineering, permit reviews can be more time consuming as they check the plans to ensure they meet today’s code and structural requirements, and construction can often take just as long and face lots of difficult conditions - all of which add cost and make these projects not as affordable as they first seem.


Garage Conversions Don’t Save You Money

Based on recent projects, we find that the cost of renovating an existing garage is often around the same as demolishing the garage and building a new ADU, and the process is much more difficult.

We find that the construction cost of most ADUs in the Portland area come in between $175,000 and $250,000 (or higher if you want higher-end finishes and products). With the cost of labor in this tight market, import tariffs, and demand on material supply, costs have gone up significantly over the past couple of years. Those numbers don't include the design fees (estimate around 10% of construction costs) or permitting fees (between $6,000 and $12,000) depending on the design and existing conditions. Even garage conversions are within those ranges. There may be some savings if the existing structure is up to code and in great condition, but rarely is that the case. Typically garages have damaged roofs or siding, no windows or existing windows that need to be replaced, insufficient structure, and often the concrete slab and foundations are cracked, damaged, or non-existent. Often, it costs the same amount to upgrade and repair the existing structure, as there are savings by reusing the garage.

Once you are spending the same amount of money, why limit yourself to working within the garage rather than designing a custom ADU that can be more beautiful, responds specifically to your needs, and fits in better with your property?


New Construction can be Healthier, more Comfortable, and more Sustainable

Keeping our buildings cool in the summer and warm in the winter is one of the biggest uses of energy.

With all of our projects, we approach the design process by considering how to create beautiful spaces that are comfortable for occupants, have a healthy indoor environment, and are as sustainable as possible within our client’s budget. Achieving these goals is often more complex and difficult when renovating an older structure rather than building new. Most older garages are built out of 2x4s where contemporary homes often have 2x6 thick walls, and 2x12 roofs. This extra wall and roof cavity space allows us to better insulate our buildings, and insulation is the first step in creating comfortable and sustainable buildings.

Keeping our buildings cool in the summer and warm in the winter is one of the biggest uses of energy. Increasing the R-values of our walls and roof (a higher R-value means better insulation) is the cheapest and easiest way to reduce our energy use, make our interiors more comfortable, and reduce CO2 emissions.

To achieve similar insulation values in a garage conversion project, it involves sistering new deeper studs and rafters to the existing framing - basically re-framing the entire structure from the inside. The alternative, is to simply insulate the existing wall cavities, regardless of the thickness of the structure. This leads to lower R-values, more drafty homes, and more extreme temperature fluctuation based on changing weather and outdoor temperatures. This can make the ADU feel too cold, too warm, or rely on intensive energy use to heat and cool the space. And remember, higher energy use means higher energy bills for the entire life of the building. This increased life-cycle costs is worth considering as you budget for your project.


You Don’t Actually Get What You Want

Garages aren’t designed, built, or sized for people to live in, or for the rooms and spaces we need to make a great place to live.

Being restricted to the existing size, shape, proportions, and height of a garage can be extremely limiting. When we have worked on these projects in the past, often we start the design process with our clients by creating layouts within the existing garage footprint, and they end up being frustrated when the learn more about the restriction and limitations of the design. The spaces end up being smaller than they anticipated, and the complications of adding onto, or lifting the roof to add extra space, ends up being expensive and usually far beyond their budgets. Rather than limit the possibilities by sticking with the existing garage, we encourage our clients to build a new custom ADU that responds specifically to their wants and needs, and the unique aspects of their property.


Converting a garage into an ADU has a time and place. Sometimes it is the only option to create a second unit based on the property. Other times the garage is newer and in great shape and can be more easily converted within a tight budget. However, the vast majority of the time, in our experience, these projects are more trouble than they are worth and don’t actually save any money. It is for those reasons that we usually recommend designing and building a new ADU that is exactly what you want, rather than limiting yourselves to working within the existing confines of a garage structure.

If you have questions or want to discuss some particulars about your unique situation, don’t hesitate to contact us. If you are considering adding a new ADU to your property you can schedule a consultation here:

If you are looking for more information about ADUs and our design process, project costs, and services check out our ADU page: https://www.propelstudio.com/accessory-dwelling-units-adu/