We frequently get contacted by people looking to add a wide range of ADUs types, but the two most common are new construction detached ADUs, and Garage Conversion ADUs. This seems to be the case in almost every town and city that allows accessory dwelling units. People who have garages in place think converting them to a rental unit would be a great option. While others hope to build an detached ADU in their backyards. Here we will discuss some of pros and cons of both of these ADU types and ultimately why we recommend going with new construction rather than converting garages for most properties.

New Construction ADUs

Ease

If you are thinking of adding and ADU to your property, Detached ADUs (sometimes shortened to DADU) are by far the easiest path forward. It is always more challenging to work within existing conditions and going with a detached ADU also gives you the most flexibility with the design and layout. New construction allows the design team to respond to the unique aspects of your site and the specifics of what you want your ADU to look like and accommodate. It is the easiest option for designers and builders and probably the best option for you to get exactly what you want.

Quality

Today’s construction techniques and consideration of modern building science can give you a high quality ADU that is efficient and sustainable. In almost all cases this will result in a higher quality project than working within an old garage that probably wasn’t built to today’s codes or standards. From increased insulation, to tighter building envelops, building new will give you the highest quality end result.

Flexibility

Alluded to in the ease section above, detached ADUs often give you the most flexibility when it comes to size, height, form, and layout. They can be designed custom for your property and the end use of the ADU. The size isn’t restricted to fitting within an existing structure so is only limited by the local regulations for ADU size. Same for style. Detached ADUs can range in style from traditional to modern and designing a custom detached project gives you the most flexibility.

Cost

Many people will say that you can save money by converting an existing structure rather than building new. Although this may be the case in some specific circumstances, for the most part we have found that the cost often ends up the same and sometimes conversions actually cost more. It is complicated working within existing spaces, and often there are specific requirements to bring older structures up to today’s codes, which can be incredibly costly. Making sure that the foundations are sound, insulation requirements are met, and utilities can reach the right locations can be much harder when working within an old garage or basement. Building a new construction detached ADU could potentially be a more affordable option.

Start with a Pre-Designed ADU Plan

With a detached ADU you have multiple options for how to move forward with the design. You have the option of going with a fully custom design that is specific to your needs and property. You also could start with Pre-Designed ADU Plans like the ones we sell on this site. This option could save you a lot of time and money. ADU Plans aren’t right for everyone, but if you are looking to keep cost down and are willing to stick to the designs available it could be a great option.

Increased value

Converting existing space, be it a garage or basement, doesn’t really add more usable space to your property. In many cases it is replacing one use with another - you may gain a rentable unit but lose storage or parking. To maximize the increased property value of adding an ADU a new construction detached ADU may be the best option. It gives you a new asset while maintaining the use of those other spaces. Further, depending on the jurisdiction you may be able to add a detached ADU as well as convert a basement into a JADU, giving you three units on one property. Our point here is that adding a detached ADU gives you the most potential to maximize the use of your property and increase the value.

Garage Conversion ADUs

Complex

Converting existing spaces is complex as you are constrained by space and access. It is harder to achieve structural requirements like seismic bracing or energy code requirements for insulation as two examples. Often these and other requirements result in almost rebuilding the whole structure, negating any potential savings. In other cases, conversions may be more labor intensive for things like foundation repairs or slab demo and re-pours than they would be on a new construction project. The added labor cost often negates any potential savings of using the existing structure to reduce material costs. Both the design and construction of garage conversion ADUs are complex and typically more complicated than most people assume when the consider this option.

Limited size

If you are going to invest a significant amount of money on an ADU project, it makes financial sense to maximize the size. You will get a greater return on the investment with a larger ADU - either through increased rental income or higher property value increase. However, converting a garage inherently limits the size of your ADU as you are stuck working within an existing footprint. Further, garage dimensions are set to be an efficient way to park a car, not as an efficient use of space for living. One car garages can maybe fit a tight studio apartment while a two-car garage could potentially accommodate a one bedroom unit. However, both are limiting in terms of potential use and rental potential. You will get a better layout and more space if you skip the conversion and just go with a detached new construction ADU.

Cost

As discussed above, but worth repeating here, we have found through years and years of experience that converting garages are not nearly the savings that most people assume. Most garages are old and in disrepair. Very seldom are the siding or roof worth keeping and most often the foundations and slab are not up to codes for living spaces. Working within an existing structure can also dramatically increase the labor time as it limits access for machines and equipment. Once you factor in all the required upgrades and code requirements it often means you are basically rebuilding the whole structure anyway, but arbitrarily limiting the size and footprint of your ADU. And the fees for doing a custom design would be higher than if you started with pre-designed plans for a detached ADU. The cost savings, if there is any at all, is not worth the limitations.

Custom design

You can’t do pre-designed solutions for garages or other conversions. There are too many custom requirements and details needed that you will have to hire a design team to do a custom solution. This eliminates the ability to use pre-designed plans. Although custom design often can lead to the best result for the specifics of your property, it is definitely a more expensive path than starting with an ADU design that is already completed.

Property value

By converting a garage you gain an ADU but in the process you lose a garage. Overall this may end up adding some value to the property, but you are subtracting one asset to add another. To maximize the value of the property it is better to add a new ADU.

Our Recommendation

Based on almost 10 years of experience working on ADU projects, we have some strong opinions on the best way to get a high quality project. For most people going with a new construction ADU will give you the best result. New Construction offers the most design flexibility to get what you want, it can add the most value to your property, and it can lead to better quality construction and a higher performance building. Although for some properties a garage conversion may make sense or may be the only option, for the vast majority of people looking to add an ADU to their property, we highly recommending choosing to go with a new construction Detached ADU, whether it is a predesigned ADU Plan or going with a fully custom design.