Attached ADU Design: Advantages and Disadvantages
In our previous articles, we explored the different types of ADUs and their benefits for various types of homeowners. But before diving deeper, it’s important to briefly answer the question: What is an ADU?
An ADU, or Additional Dwelling Unit, is a secondary residential space built on the same lot as a primary home. It can be attached to or detached from the main house and serves as an independent living area with its own entrance, kitchen, and bathroom.
This time, we’ll focus on the Attached ADU, a type of Additional Dwelling Unit that shares a wall with the main house. Typically, smaller and more affordable to build, attached ADUs offer unique advantages—but also come with certain limitations, such as reduced privacy for tenants. We’ll look at real project examples to see how thoughtful design can turn underused spaces into valuable, functional units and how smart architecture can overcome the challenges of building on an existing structure.
Advantages and Disadvantages of Having an Attached ADU
Understanding Attached Additional Dwelling Units
When deciding to construct an ADU, it is important to know what type of ADU suits you best in order to get the maximum advantage from the unit. As mentioned before, attached additional dwelling units have at least one shared wall with the main house, which offers a variety of advantages for homeowners. The size of these units is usually smaller than detached units and they are typically constructed on smaller lots. Attached ADU floorplans create additional space that blends easily into the main house. Attached ADUs can have a maximum size of 1,000 sqft, depending on the area of the lot.
Quoted from Site halfmoonbay.gov about What Is An Attached ADU:
According to the California Government Code, an ADU is an attached or detached residential dwelling unit that provides complete independent living facilities for one (1) or more persons and located on a single lot with a proposed or existing single-unit dwelling
Main Benefits of Attached ADU Design
One of the main benefits of these units is that, in ADU house plans, you don’t have to construct a private bathroom or toilet—the ADU can share a bathroom with the main house. This feature can reduce construction costs significantly since there is no need for new plumbing. Also, since these ADUs are attached to the main house, they require less area, making them ideal for smaller lots. Attached additional dwelling units are most suitable for multi-generational households since they provide more privacy through features such as separate entrances or, in some cases, separate toilets, while still maintaining family closeness. This ADU design is also a great option for hosting guests or creating an office space where the homeowner can work remotely while maintaining privacy and focus. Increasing property value is another benefit of the attached ADU. It is important to have a well-thought-out ADU design to maximize the potential increase in property value.
Challenges and Design Solutions Attached ADU
While offering several benefits, attached ADUs also have some disadvantages. These units have less privacy compared to other types of ADUs, which can cause difficulties when the homeowner decides to rent the unit for additional income. Tenants usually prefer to have a private space with separate kitchens and bathrooms, and having to share these facilities can be problematic. Having a shared wall also means that noises from the main house can be heard in the unit and vice versa, which can be a negative point for people who want to rent—especially students or remote workers. However, many of these disadvantages can be reduced or solved with a thoughtful ADU floorplan. Although it might increase the initial construction cost, it will bring financial benefits in the long run.
Corona ADU by FASTBUILD
*Overview of the Corona ADU Project
One of the great examples of an ADU design is the Corona project in California. The existing garage was converted into a unit that can be rented to generate additional income for the homeowner. The picture below illustrates the existing floor plan of the house, and the location of the proposed ADU is marked by a red line.
*Design Features and Layout
As you can see in the plan view, the garage space of the building was transformed into an ADU which, compared to other attached ADUs, is completely private—making it a very suitable option for rental income. The existing toilet in the house was designated exclusively for this unit; furthermore, a kitchen and a bedroom were also added, providing all the amenities needed for someone seeking a private living space. The unit has its own private entrance that opens into the kitchen and living room. It features an open ADU floorplan, which allows the space to be reused in different ways in the future. This flexibility can greatly increase the property’s value.
*Benefits and Cost Efficiency
The quality of the walls makes the unit more soundproof, providing a calm and relaxing environment for tenants. Since the unit was constructed within the existing garage space, the construction cost was significantly reduced. Even with the installation of a new HVAC unit, the overall expense was much lower than building a detached ADU. Additionally, the project maintained one parking space for the homeowner. The picture below shows how the unit came together—despite its small size, this ADU design still looks spacious and comfortable.
Conclusion
To sum up, the focus of this article was the attached additional dwelling unit. After defining the concept, we discussed the benefits and disadvantages of having an attached ADU floor plan.
When having an ADU in Los Angeles, it’s crucial to understand how each type differs in order to choose the one that best addresses your needs. Attached ADUs are most suitable for homeowners with smaller lots who need extra space for a home office, guest house, or a private area for children. Since they usually offer less privacy, it can be a bit more challenging to manage rentals with an attached ADU house plan. However, this issue can be resolved by having a thoughtful design that addresses these concerns.
The attached ADU in Corona by FastBuild is a great example of how a well-designed ADU floor plan can solve these issues, providing both an additional income source for homeowners and a comfortable, private space for tenants. The open floor plan allows the homeowner to repurpose the space in the future. Even with the installation of a new HVAC unit, the construction cost of the unit remains lower than that of a detached ADU, while still leaving space for parking on the lot.