Before 2020, only single-family lots were allowed to add an ADU, which meant multi-family lots were left in the dust of the ADU boom. Times have changed and the opportunities for multi-family lots have really taken off!

If you own a multi-family dwelling, you can potentially add multiple ADUs to your property. You can earn more income or create a family compound. Many folks aren’t aware of these changes in the state regulations, so let’s unpack them.

What makes a dwelling “multi-family?”

It is not the property or the zoning that makes a dwelling “multi-family.” It’s the structure.

This is something a lot of our ADU clients get confused about.

To be classified as multi-family, a structure must consist of two or more residential dwellings that are attached to one another. If you have two or more houses on a single lot but they are NOT attached, they are not considered multi-family dwellings.

If you own a duplex with two units that ARE attached, it is multi-family. So are triplexes and fourplexes—any dwelling with attached units. Apartment buildings are multi-family.

Which multi-family dwellings qualify for the new ADU regulations?

Your lot must be in a residential zone. The type of residential zone does not matter. Your parcel cannot be zoned as industrial or anything that is not residential. For example, if you own a duplex or apartment building that is in an industrial zone, even though that structure is multi-family, you can’t take advantage of the ADU multi-family opportunities.

multi family adu

How many ADUs can you build on a multi-family property?

Your options depend on your jurisdiction. Local agencies must allow you to build at least one ADU out of existing accessory space in your primary structure or two detached ADUs on the property. Some jurisdictions allow you to do both. And some allow you to build much more.

A “detached” ADU means one that is detached from the main structure. In some jurisdictions, the two detached ADUs can be attached to each other. But there are jurisdictions that insist the detached ADUs be stand-alone.

“Accessory space” is an area that is not currently permitted as living space. This includes covered garages, utility rooms, storage rooms, community rooms, basements, and attics. You can also convert detached accessory spaces, like a clubhouse or carport.

You can’t convert spaces that are currently living spaces into ADUs. For instance, if your building has a large apartment, you can’t divide it in two and call one of them an ADU.

You also can’t convert uncovered parking (like a parking lot).

Multi-family ADUs galore: the famous formula

Every multi-family dwelling is allowed at least one ADU converted from accessory space or two detached ADUs, and sometimes both. Where things get really interesting is for buildings with 8 or more units. In the best-case scenario, your jurisdiction could allow you to convert a number of ADUs equal to 25% of the number of units in your building, and also let you build two detached ADUs.

Let’s say you own an apartment building with 20 units. If your jurisdiction allows, you can convert accessory spaces to five ADUs—five is 25% of 20. If you have enough space on your lot, you can also build two detached 800-square-foot ADUs.

It all depends on the jurisdiction. That’s why it is crucial to hire a design team that knows how to thoroughly research your local ADU regulations.

Interested but confused? Call Maxable for a Site Evaluation and we’ll untangle the regulations and show you what you can build.

What size can these ADUs be?

The minimum size is 150 square feet and the maximum is 800 or less, depending on your jurisdiction.

What if your jurisdiction allows you to use the 25% rule, and your building has 20 apartments and 20 garages that you could convert to ADUs? Does that mean your five new ADUs each must be the size of a garage?

No. You could take any number of the garages—even all 20 of them— and turn them into just a few ADUs.

Remember, the accessory space doesn’t have to be a garage. It can also be a storage room, utility room, basement, attic, community room, etc. Anything that was not originally permitted as living space.

multi family adu living room

Parking for ADUs on multi-family lots

You don’t need to provide parking for the ADUs if the property is within ½ mile of public transportation or one block of a car-share vehicle. This is true even if you convert garages into ADUs. No parking is required for ADUs created out of accessory space within the multi-family structure.

Where will your tenants park? As a landlord, that’s a trade-off you’ll need to think about. Some properties have space for a parking lot. There may be ample street parking nearby. Other multi-family dwellings are in urban settings where the tenants don’t always own cars.

Unsure about multi-family regulations? Book a Site Evaluation and our ADU expert will walk you through your options.

How much will it cost to build ADUs on my multi-family property?

When designing and building multiple ADUs, you may be able to benefit from some economies of scale. We work with large property owners who have their own construction crews, which is a huge advantage in terms of managing time and labor costs.

How you connect the utilities—whether each will have a separate meter, and what utilities might be included in the rent—will have an impact on the end cost. In building multiple ADUs you may also exceed capacities for utilities, and that can be costly.

Above all, working with people who understand the regulations will save you time, and that saves money.

multi family adu kitchen

Multi-family ADU laws are new and evolving–so get an expert to help you!

Adding ADUs to a multi-family property presents terrific opportunities. But it should never, ever be a DIY project. The complexity of the regulations makes it essential to get guidance from a team experienced in designing and permitting ADUs.

Jurisdictions across the state are writing ordinances that will affect the scope of your project. It’s your design team’s responsibility to figure out the path of least resistance with the city and show you that path. You may decide to push the city’s limits, but you still want to be as informed as possible. Is maxing out the property worth potentially delaying your project for many months? Will it pencil out?

The more experienced your design team, the fewer surprises you’ll be in for. And the faster you’ll see a sweet return on your investment!

garage to an adu