All ADU Resources

Different types of ADUs

There are several different types of ADUs: Detached ADUs, Attached ADUs, & Conversion ADUs. Click to explore the differences & know what is right for you.

April 10, 2021

Accessory Dwelling Units can come in many different shapes and sizes - there's a Detached ADU, Attached ADUs, Converted Space ADUs / Conversion ADUs, and then there are Junior Accessory Dwelling Units AKA Junior ADUs or "JADUs." How do you know which is which, and which one is right for your needs?

Summary of ADU Types

Here is helpful graphic summarizing the different kinds of Accessory Dwelling Units out there:

As you can see, ADU units can come in many shapes and sizes, and there is no one-size-fits all approach to the ADU that's right for you! Here's a few examples of how Cottage has helped homeowners like you build the accessory dwelling unit that was right for them and their primary residence, with links to each of these featured projects:

Detached ADUs

Detached ADUs are backyard cottages detached from any structure on a property. Detached ADUs are great for maintaining privacy for a renter or maintaining an independent lifestyle for families living together on a property. Because these units stand separate from the main house on their own open space, new construction tends to be more straightforward - not dependent on the quality or conditions of the primary dwelling or garage.

A few examples that Cottage has worked on: A longtime Los Altos resident wanted a custom craftsman 1-bedroom ADU for their daughter. A Santa Clara family wanted a 340 sq. ft. tiny home to bring the in-laws closer to home. A Berkeley property investor wanted a duplex ADU for rental income.

Attached ADUs

Attached ADUs are in-law units or rental units attached to the main house or another structure. Mostly, homeowners seeking Attached ADUs do so to maximize their lot coverage by eliminating any setback between the granny flat and the main house. Keep in mind that attached ADUs may require fire-rated separations between the ADU and the main single-family home, adding cost and increasing the potential of needing to update the wall adjoining the main house and the ADU.

One example of a Cottage attached ADU project: A South San Francisco Property owner wanted to build a 600 sq. ft. ADU in a tight space for more rental income.

Conversion ADU or JADU

Conversion ADUs are ADUs built into the existing house structure to become an ADU. In California, most Conversion ADUs are garage conversions, but other options could be converting a basement, attic, or even a spare bedroom into an extra unit for rent. These are usually very cost-efficient ways of adding ADU space to your home - with most two car garages, you can add an ADU whose floor area has a square footage of 400 at 60% the cost! These have floor-area-ratios at a great ADU cost.

Two recent examples of Cottage conversion ADU projects: A Palo Alto family hoped to convert their 2-car garage into a spacious ADU. An Oakland couple wanted to use the existing footprint of their 2-car garage for a spacious 1-bedroom ADU or JADU.

JADUs are smaller ADUs that have relaxed regulations and ordinances for bathrooms and kitchens, usually at a maximum of 500 sq. ft. JADUs must utilize existing space within the main structure of your home so while attached garage conversions would qualify, detached garages usually won't! The main difference between a Conversion ADU and a JADU is that JADUs allow for efficiency kitchens (a hotplate / microwave vs. a cooktop / range) and can share bathroom facilities with the main house. We've seen very creative JADUs built out of converted extra bedrooms and guest spaces!

So what kind of ADU unit is right for me?

We like to ask all the homeowners that come to us about their ADU vision the question: "What is the use case for your ADU?"

If you're hoping to use the ADU unit for rental income, privacy from the main home may be something to think about. If you are looking for a space for the in-laws, you may want an accessible ADA-friendly ADU that has a larger bedroom and bathroom. Or if you are staring at your empty garage wishing it could do more than store the kids' old bikes, then a garage conversion could be right for you.

Oftentimes, your choices may be limited by the size or shape of your backyard or existing structures. However, over 3,000 ADUs across the state have been built on lots of 5,000 square feet or less, proving that room for more can be made with even less than you may have thought!

How does Cottage help with your ADU?

Because Cottage is a fully custom, stick-built ADU company that builds ADUs from the ground up in the same way as your existing home, we help you build the ADU that is right for you and your property. From eligibility to design to permitting to construction, we guide you through the process from start to finish. Check out our Featured Projects to see how homeowners like you have used their existing backyard, garage, or other available space to build their ADU from start to finish, customized to your specific needs.

Ready to talk more about how Cottage can help build the ADU of your dreams from start to finish? Contact us today using the link below for a Free, No-Obligation Consultation & Estimate with one of our ADU experts!