The most popular types of ADUs are detached ADUs (a separate new structure), garage conversions, attached ADUs (sharing a wall with the home), and junior ADUs (within the existing walls, up to 500 square feet). Each fits a different budget and lot. Here’s a guide to the most popular ADU types.
Accessory Dwelling Units (ADUs) are a popular way to expand living space, increase property value, or generate rental income. When it comes to building an ADU, homeowners typically consider two main approaches: prefab (prefabricated) construction and stick-built (traditional) construction. Each method has its own benefits and challenges, so your best option depends on your budget, timeline, and property specifications.
If you choose traditional construction, you can build several types of ADUs, including detached units, attached additions, garage conversion, and more.
Jump To Tradition Construction ADU Types
If you need a basic overview of what an ADU is, check out our Step-by-Step ADU Guide to get the basics down. Then, come back to learn about the specifics of which type of ADU is right for you!
Here at GreatBuildz, a free service that connects homeowners in California with reliable ADU contractors, we speak to homeowners every day about planning for an ADU construction project – here are some considerations to get you started.
Understanding ADU Construction Approaches: Prefab vs. Stick-Built
Prefab ADUs
Prefab ADUs are factory-built units that are transported to your property and assembled on-site. This method is growing in popularity due to its speed and cost efficiency. Since much of the construction occurs in a controlled factory environment, weather delays are minimized, and the assembly process is streamlined. Prefab ADUs often come in modern designs and somewhat customizable layouts, making them an attractive option for homeowners seeking a fast turnaround and sleek aesthetics.
However, prefab ADUs have limitations regarding customization and adaptability to unique property layouts. Transportation and crane installation can also add costs, particularly for properties with challenging access points.
Stick-Built ADUs
Stick-built ADUs are constructed on-site using traditional building methods, allowing for maximum customization. This approach is ideal for homeowners with specific design requirements or those with irregular lot shapes where prefab units might not fit. Stick-built ADUs can match the existing architecture of the property, offering a cohesive look and feel.
Stick-built ADUs use construction materials that have been relied on for generations, ensuring durability and long-term performance. These materials have been tested over time and are well-understood by builders, reducing the risk of unforeseen issues. The traditional building methods used in stick-built ADUs are the same as those used in primary home construction. This means most contractors are already highly skilled in the process, leading to reliable craftsmanship and fewer construction uncertainties.
While stick-built ADUs provide design flexibility, they typically require more time to complete and may be affected by weather conditions. Costs can vary based on labor, materials, and permitting requirements.
Panelized Construction: A Hybrid Approach
In addition to the popular prefab and stick-built methods, panelized construction is a newer concept in the ADU space. This method offers a hybrid approach that combines the efficiency of prefab with the customization potential of stick-built. Panelized ADUs are constructed using pre-manufactured panels that are delivered to the site and assembled like a big LEGO.
One of the key benefits of panelized construction is the reduction in build time compared to traditional methods. Since the panels are manufactured off-site in a controlled environment, the assembly process is quick and less susceptible to weather delays. This efficiency often results in cost savings on labor and materials. Unlike fully prefabricated units, panelized construction allows for greater customization. You can work with designers to create layouts and features that suit your property’s unique needs while still benefiting from a streamlined assembly process.
Panelized ADUs are often more eco-friendly, as factories can minimize waste by using advanced technology and precise measurements during panel production.
Finding the Right Fit
Ultimately, the choice between prefab and stick-built ADUs depends on your priorities. If you value speed and modern aesthetics, a prefab ADU might be the right choice. For those prioritizing customization and time-tested building methods, stick-built construction offers unmatched flexibility.
Traditional Construction Types of ADUs
1. Detached ADUs
A Detached ADU is a separate living space on your property. They are stand-alone buildings and provide great privacy for both the people living in them and those in the main residence. This privacy makes detached ADUs very attractive for homeowners who plan on living onsite. Homeowners can use these types of ADUs to accommodate family members or generate rental income without losing their own personal space.
Though they usually need a bigger investment because they require their own construction and utility setups, detached ADUs can bring significant value. Their privacy and roominess make them very appealing to renters, which helps increase rental income and enhances the value of the whole property.
2. Attached ADUs
Attached ADUs, unlike detached ones, share at least one wall with the main house. This connection helps save money during construction because it’s so close to the existing utilities. These types of ADUs work well for homeowners who are looking to convert their property into more of a typical duplex property. These spaces are perfect for multigenerational living or housing visiting family members.
You can make attached ADUs by adding to the side or back of the house or by converting garages. Although there may be fewer design choices with attached ADUs compared to detached ones, they provide a smart way to add useful living space without much effort.
3. Garage Conversion ADU
Garage conversions are the most popular type of ADU! This is because they are an efficient use of space and one of the most cost-effective methods of adding an ADU to your property. Homeowners can change an existing under-used garage into a comfortable living space.
Garage conversion ADUs are good for:
- Rental Income: Making an independent rental unit with a separate entrance.
- Home Office or Studio: Creating a workspace that is separate from the main house.
Converting a garage into an ADU is cheaper and takes less time to build than the other options discussed above. These types of ADUs are a great option for homeowners who want to get more out of their property without spending too much.
4. Basement Conversion ADU
Basement conversions are a smart way to add an ADU while using space you already have. This process changes an often-unused basement into a usable living space. Just like garage conversions, basement conversions make use of the existing structure. This can save you money and time during construction.
One big benefit of basement conversion ADUs is that they don’t add any ‘built-space’ to your property. This helps especially for those with smaller lots or people who wish to keep their yard space. Still, it’s important to make sure there is enough natural light and fresh air. Using larger windows, light wells, or skylights can greatly help with this.
5. Above-Garage ADU
Above-garage ADUs use the space over a garage to create a private living space. This is great for homeowners with small lots. It helps them make the most of their property’s square footage without giving up yard space.
Above-garage ADUs are useful for different needs. They can be comfortable places for guests, studios for artists or hobbyists, or even rental units, depending on local rules. Being higher up can also give nice views and more natural light, making the living experience better.
However, homeowners need to understand that there will always be a cost increase when ‘building up’, especially on top of a garage. Since the structure wasn’t initially built to handle the load of a second story, there will be added costs to strengthen the foundation and structure, as well as adding stairs to get up to the new unit.
6. Interior Conversion ADU
Interior conversions are a smart way to create an ADU. They change existing spaces inside your main home. This method is budget-friendly and works well in areas like spare bedrooms, large closets, or parts of a finished basement. It is great for homeowners who want a separate living space without more construction.
These types of ADUs are perfect for aging family members who need to be close to the main living area. They also work well for older children who want privacy. Homeowners can use these types of ADUs to set up home offices, workshops, or studios without spending too much on construction.
7. Junior ADU
A Junior Accessory Dwelling Unit (JADU) is a smaller, self-contained living space that is typically created by repurposing a part of an existing single-family home, such as a converted bedroom or garage.
It is technically the same thing as an interior conversion discussed above, however, there are a few specific nuances when it comes to Junior ADUs. First, they are limited to a maximum size of 500 square feet and often share utilities with the main house. They are not required to have a dedicated bathroom, as long as another bathroom is accessible from the space. Finally, these types of ADUs are allowed in addition to another ADU on the property. That means with a JADU, you can convert a single-family home into what is essentially a tripex!
They are the most cost-effective way to add another living unit to a property, providing housing for extended family members, generating rental income, or offering an affordable housing option in areas with high housing demand. JADUs are popular for their ability to maximize space without requiring extensive new construction.
Ready to Build an ADU?
Learning about the different types of ADUs can give property owners new ways to use their living spaces better. Each type of ADU has its own benefits. There are detached structures that offer privacy and garage conversions that can create extra living areas. Looking into the various options will help you understand which option best matches your needs.
By adding any ADUs to a lot, property owners can change their spaces to fit their specific needs. If you are thinking about adding an ADU, our ADU Experts can help you decide on the best options for you.
Frequently Asked Questions
What are the main types of ADUs?
The main types are detached ADUs (a standalone structure), attached ADUs (sharing a wall with the main home), garage conversions (converting an existing garage), and junior ADUs (up to 500 square feet within the existing home). Each suits a different lot, budget, and goal.
Which type of ADU is cheapest?
A junior ADU or garage conversion is usually the most affordable, since both use existing structure. A garage conversion typically costs $120,000 to $150,000 and a JADU $50,000 to $100,000. A detached new-construction ADU costs the most, $150,000 to $400,000, but offers the most flexibility.
Which ADU type is best?
It depends on your lot, budget, and goals. Detached ADUs offer the most privacy and flexibility, garage conversions reuse existing space affordably, attached ADUs are cost-effective when tied to the home, and JADUs are cheapest but smaller and require owner-occupancy. Your priorities guide the choice.
When it comes to planning and coordinating an ADU construction project, you shouldn’t have to go it alone – GreatBuildz is a free service that connects homeowners in California with reliable, thoroughly screened ADU contractors and provides project support from start to finish. Give us a call at (818.317.3567) or submit the form below to begin your ADU journey!
