A Guide to Building an Accessory Dwelling Unit ADU in Multifamily Properties
In this post, I will cover all you need to know about building an ADU in multifamily properties and share my experience with different projects we’ve worked on.
A multi-family property is any property that has more than 1 house: duplex, triplex, quadplex and above. I will talk about the ADU requirements and ADU permit process for multi-family properties.
Introduction
Welcome to the exciting world of ADU Accessory Dwelling Units in multifamily properties! These private living units offer a unique opportunity to increase income, house loved ones, or even create a multi-generational living space.
Chances are, if you own a multi-family property, it’s either an investment property or you live in one unit and rent out the other. That’s house-hacking and such a smart idea. That is exactly how my husband and I started our real estate investing journey and it gave us some level of financial freedom.
But navigating the regulations and possibilities can be overwhelming. This guide is your roadmap to unlocking the potential of Building an ADU in your multifamily property. Let’s start with defining what an ADU is. And if you have a single-family property, check out these related posts:
Guide to Building an ADU Accessory Dwelling Units
ADU in Single Family Properties
Junior ADU in Single Family
What are ADU Accessory Dwelling Units?
ADU, or Accessory Dwelling Unit, is another house located on the same property as a single family or apartment (multi-family property). Think of them as mini-homes within your existing property, complete with their own kitchen, bathroom, and living area. They can be attached to the main structure, detached, or even converted from existing spaces like garages or basements.
Benefits of ADU Accessory Dwelling Unit in Multifamily Properties:
- Increased income: Renting out an ADU can provide a significant boost to your rental income. This works if your property is large to accommodate another unit or you want a better use of the existing garages in your property.
- Flexibility: Use the ADU Accessory Dwelling as a guest house, in-law suite, home office, or even a rental property for short-term stays. Please check with your jurisdictions as most multi-family properties fall under rent control laws and therefore not eligible for short term stays.
- Enhanced property value: Adding an ADU Accessory Dwelling Unit can increase the overall value of your multifamily property, making it more attractive to potential buyers or renters in the future. You can easily increase your unit count without spending what a property cost.
- Community building: No one really talks about the benefits of building a community through multi-family properties. ADUs can help to add density and diversity to neighborhoods, promoting walkability and reducing sprawl. A community is something I want to incorporate in my design and investing moving forward.
Types of ADU Accessory Dwelling Unit Allowed in Multifamily Properties:
Before we jump into the different types of Accessory Dwelling Units I want to preface with a brief overview of the general requirements for Building an ADU in a multifamily property. These are:
- You can build 1 attached ADU (or up to 25% whichever is greater) and 2 detached ADU units
- If converting within existing space, the setbacks and distances remain
- If adding to a structure, or building brand new, side and rear setbacks are 4-feet and building separation should be at least 6-feet from all other structure
- No parking required if within ½ miles of public transit
- Maximum height of conversion remains as is
- No maximum size on conversion and No stated maximum size on new construction (as of yet)
- Maximum height is 18-feet if you’re within ½ mile from public transit and you can add an extra 2-feet to match the roof of the structures on site. This easily allows for 2-story ADU Accessory Dwelling Units
- No fire sprinklers required if the existing units don’t have it. However, this varies for your zone. If you’re in a very high hazard fire zone you will most likely require fire sprinklers
- No owner occupancy required
For a deeper review about the General Requirements for Building an ADU, please check out this related post. Now onto the types of ADU units you can build in a multi-family property.
Converted ADU Accessory Dwelling Unit
One of the most common types of Accessory Dwelling Unit is the ADU garage conversion. It transforms existing space like garages, basements, or attics into functional living units. This can be attached or detached.
Keep in mind that you’re allowed 1 attached ADU unit and 2 detached ADU units.
I like to illustrate this concept with real life projects that I’ve worked on and the creative solutions I found for my clients looking to maximize the rental potential of their income property.
Example 1: Existing Garage Conversions to (2) ADU plus (1) Attached Carport Conversion to ADU
I have a client with a large lot with 3 separate structures on it: (2) single family houses and (1) duplex. This quadplex qualifies as a multi-family property. The property had the following structures that the owner wanted to convert into ADU Accessory Dwelling Unit:
- 4-car carport at the back of the property (standalone)
- 1-car garage attached to a rec room structure (standalone)
- 2-car carport attached to a single house
The process of turning the detached 4-car carport and the 1-car garage with recroom was very straightforward and easy. My client had the option to add more square footage, something he declined because it didn’t make sense with the layout of the lot.
However, the 2-car carport was harder to achieve and had much more steps involved! I learned a ton from this experience.
Our first issue was that the existing 2-car carport was attached to the single family and not the duplex. Instead, it was attached to single-family, thus ineligible for the Attached ADU option. So we built a breezeway between the 2-car carport and the duplex nearby.
Our second issue was that if we turned the 2-car carport into an ADU, it would turn the duplex plus the attached ADU plus the attached single family house into a 4-unit apartment, thus triggering more stringent fire separation rules and potentially needing to add sprinklers to the newly created 4-unit apartment.
Our third issue was that we could not ADD to the attached ADU. In this instance, my client wanted to add to this attached ADU. When you convert from within a multi-family structure, you can only convert, not add. Disclaimer: this is in the City of Los Angeles so every jurisdiction varies.
Our solution
- Demolish the existing 2-car carport attached to the existing single-family house
- Propose a new and larger carport with a breezeway attached to the duplex
- Build this new carport and breezeway first and get Certificate of Occupancy
- Convert the new carport into an Attached ADU unit
I’m happy to announce that the carport is under construction, so our next step is to apply for the garage conversion into ADU as soon as it’s done.
Example 2: Garage and Storage Conversion into ADU, no maximum
My client approached me with wanting to convert a rather large, 1,300 square feet 2-car garage with an attached storage/hobby shop into an ADU Accessory Dwelling Unit. There is another unit above this garage and storage.
She worried that the city wouldn’t allow to convert such a large space into an ADU Unit because of the maximum of 50% of the attached structure and the maximum 1,200 square feet limit. We dispelled her fears by assuring her that there is no maximum for conversions within existing structures. And we proved it right when the city planning department approved our plans for the conversion.
At the beginning there was pushback from the city planner because of the 1,200 square feet maximum size. However, I read through their ADU requirements and documents and found a passage where it mentions no maximum if converting within existing structure.
Pro tip: do your research and due diligence! ADU Accessory Dwelling Units are relatively new so there are lots of myths and misunderstandings to educate planners, designers and homeowners on. It never hurts to ask questions to your city planners. I do it ALL THE TIME and most planners are happy to help. That’s what they’re there for!
Example 3: My own attached ADU in my duplex property!
We bought and renovated my first property purchase in 2018. It was a duplex that we added onto to make larger units. We rented the front unit to some amazing tenants and lived in the back. We designed a living room that we hardly used so we thought about turning it into an attached ADU back in 2020.
When we inquired with the planning department, it wasn’t possible to convert because back then the requirement was that it needed to be a previously “unconditioned and accessory” space. Meaning, it had to either be storage, laundry room or the like in order to quality for the conversion. In this case, it was a living room.
Fast forward to 2023 and rules change all the time! Now we’re able to turn this living room into a legal, attached ADU. We’re currently drafting up the plans so I will keep you updated on the progress and share our journey.
Pro Tip: ADU laws change all the time, for the better! What wasn’t possible last year might be possible this year. Always consult with designers, architects and city planners for updated requirements.
New construction ADU Accessory Dwelling Unit
This one is very straightforward and popular if you have the land to build. Build a standalone or attached ADU Accessory Dwelling Unit from the ground up, offering a unit with more design flexibility, modern construction, and potentially higher rental rates.
These (2) ADU can be attached to each other, or completely detached from each other. Popular options that worked with our clients are:
- Side by side, two-story townhome style
- Top and bottom units (two-story duplex) with exterior stairs
- Side by side, single story duplex
These options depend on land availability and the site layout of your property.
Watch Out for maximum height requirements though! In some cities, (2) ADU’s are only allowed up to 16-feet height. Most are allowed up to 18-feet plus 2 extra feet of height to accommodate for the roof. With these maximum height requirements, you need to be realistic about how much ceiling space to allocate for each floor.
A caveat for this height restriction is if you only build (1) ADU on your multi-family property. Then the height restriction follows that of your zone (but at least 25-feet high is allowed). One thing that I need to research is what the height requirement is if you build (2) ADU but detached from each other. Will report back.
Another thing to watch out for is any overhead electrical cables running at the back of your property. Sometimes these are moved easily by your electrical company and other times it requires an application fee and thousands of dollars to move.
Finding Resources and Support:
Don’t go it alone! There are numerous resources available to help you navigate the ADU Accessory Dwelling Unit process:
- Local ADU programs: Many cities and counties offer ADU-specific programs with financial assistance, technical guidance, and streamlined permitting processes. Check out the website of your city for support and programs.
- Architects and builders: Specialized ADU architects and builders can help you design and construct your ADU, ensuring it meets all regulations and maximizes functionality. We offer ADU design and permitting services and have contractors that we work with and recommend highly.
- Online resources: Websites and organizations dedicated to ADUs offer valuable information, case studies, and community forums, such as this blog ?
- Facebook Groups: There are lots of Facebook groups where other homeowners share their experiences designing, building and renting out their ADU units.
- Your Community / Neighborhood: Accessory Dwelling Units are becoming increasingly popular. Chances are, some of your neighbors or fellow investors might already have their own ADU’s! It never hurts to ask.
Remember: Adding an ADU to your multifamily property can be a rewarding experience, offering financial benefits, increased flexibility, and a unique living space. By understanding the regulations, planning carefully, and seeking support, you can unlock the potential of ADUs and create a valuable addition to your property.
