Duplex ADU: Multifamily Accessory Dwelling Units

Many single-family households have already used such an affordable housing solution as an accessory dwelling unit. Over recent years, ADu regulations in California have significantly relaxed, allowing the construction of an ADU on almost every type of land.

Current ADU laws offer milder requirements for parking lots, abolish several impact fees, and decrease the setbacks to 4 ft., thereby permitting accessory dwelling units on smaller properties. This applies not only to single-family property but also to duplex or apartment building property.

Let’s explore the building possibilities of multifamily units and how zoning laws and new ADU regulations affect them.

Primary Dwelling Types that Allow ADUs

If you’re a property owner, you may wonder whether your parcel is appropriate for an ADU project.

California state law dictates that homeowners can build ADUs on the following types of properties:

• a single-family lot;
• two not-attached single-family homes;
• residential structures for multiple families (two, three units, or more attached units).

In all of these cases, main units already exist on the land, so you can only build as many accessory structures as your city and state permit. Also, note that multifamily properties may consist of several pieces of land. Each piece of land allows for two dwelling units. Thus, sometimes, you may build more than two ADUs near the main structure.

Accessory Dwelling Units Nearby Duplexes

A multifamily lot is a lot that contains more than one main residence. This means that more than one family perpetually occupies the property.

An accessory dwelling unit is a separate living space located on the same lot as the primary structure. But what are the rules if there is more than one main house? If a single-family home may build two units: an attached ADU or a detached ADU, as well as a JADU, building an ADU on a multifamily lot is a bit more complicated.

Homeowners of multifamily properties can also legally build up to two dwelling units. However, in contrast to single-family ones, duplex owners have the right to build two detached ADUs, which are typically bigger than attached ADUs. Moreover, there’s a possibility for duplexes to build one ADU above the other (2-story ADUs) if zoning laws or particular property allow it.

Summing up, parcels with more than one residence provide greater flexibility than single homes when it comes to ADUs. However, they also have significant limitations as to their designs and regulations that homeowners must navigate during the ADU building process.

Kinds of ADUs for Multifamily Properties

Duplex properties permit fewer types of ADU configurations than single-family ones. If you already have a building inhabited by many people, the property owner can choose to:

Add a freshly constructed detached unit.

When building a maximum of two detached units, you can choose different layouts. For example, you can construct them side by side or one on the other to save space. However, it heavily depends on the city regulations. Some regions forbid adjacent buildings, demanding the building of ADUs within some distance between them.

Convert an unlivable existing structure into a residential one

In the process of converting units, you can create up to 25% of the already existing multifamily structures. So, if you have a detached garage and some other non-habitable structure on your property with eight residential units, you can add two conversions to it.

Generally, duplex or apartment properties grant homeowners the right to build more accessory units than single homes. But what do single-family property owners do to turn their single-family lot into something akin to a duplex using an accessory dwelling unit? It’s another very important issue to cover.

Converting Property Into Multifamily Lots

Zoning laws determine what type of property your parcel belongs to. So, basically, you can’t change its status. Nevertheless, you can always add ADU units that are almost duplex constructions located on a single-family lot.

An ADU project enables you to do almost the very same things you can do with a duplex. If you’re building an ADU in the future, you’ll be able to:

1. Rent your ADU to tenants and generate income;
2. Enjoy extra living space in your house;
3. Invite guests into a separate garden cottage rather than crowding in one bedroom;
4. Realize your vision of an additional hobby room or a workspace;
5. House your relatives long-term;
6. Invest in real estate that will rise in price.

The best thing about an accessory dwelling unit is its multifunctionality. You can make money from the land you already own and use it as a rental, or you can create a home office inside. You can allocate it to your growing children or house your aging parents to provide them with a familiar environment.

Frequently Asked Questions — FAQ

Can an ADU be a duplex in California?

Although they may look similar, ADUs do not qualify as duplexes. ADUs can be independent structures, extensions of existing houses, or garages converted into living units. However, an ADU has a different legal status in comparison with a duplex.

What is the difference between an ADU and a duplex?

ADUs are self-contained units located on the same land as the main residence. Duplexes are separate households inhabited by residents who belong to different families, while ADUs are just secondary structures in the same household.

Does Sacramento allow ADU?

Yes, Sacramento certainly allows ADUs. Homeowners in California can build ADUs from scratch or have their existing garage converted into a residential unit with all amenities. In Sacramento, you can use an ADU for your own purposes or rent it out to tenants.

How much does an ADU cost in Sacramento?

If you decide to create an ADU in the Sacramento neighborhood, you’ll need financing. Depending on the type of ADU, you’ll pay the sum of around $90,000–250,000. If it’s a converted garage, it may require around $100,000, while if you opt for a new ADU, it may cost from $250 to $400 per sq. ft.

Is owner occupancy necessary to build an ADU?

Since September 2023, ADU regulations in California have not required owner occupancy to build an ADU. However, if you want to have both your ADU and JADU (junior ADU) rented out, you need to follow this rule to ensure compliance with the law. Otherwise, you can only rent out your attached or detached ADU.