SB9 - Lot Splits and Duplexes in California

What is SB9?

California’s newest housing bill makes it easier for homeowners to build more housing and, under certain conditions, split their lots into two lots.

If you can combine both parts of the law, you can split a lot into 2 lots and build 2 units on each - for a total of 4 units.

And if the city is very friendly, you might be able to do more…

SB9 has two important parts that we’ll talk about here:

Urban lots zoned for one single-family home that can now build a second home
Urban lots larger than 2400 sq ft that can now be split into two lots

Then we’ll go into a few specific topics based on the questions we’ve gotten from our clients:

Who can use SB9 and who cannot?
How does this interact with Accessory Dweling Units (ADUs) and Junior ADUs?
What is the owner occupancy requirement for SB9?
How do I learn the tax implications of using SB9 on my lot?

How To ADU exists to help homeowners who want to create more housing security for themselves, their family and/or their communities - so we’re reading this law eagerly.

I’m in direct contact with lawmakers at the state and local level, as well as the authors of the bill, so that we can get the most accurate and detailed answers possible. But it’s a work in progress!

I’ll be adding to this as we go because we are all learning on the go with this new law.

This is all general information based on my working notes, so you should not treat it like legal advice for your specific situation.

SB 9 Second Unit Explained

Summary: Many lots zoned for just 1 single-family home, can now build 2 single-family homes or a duplex.

The first section of SB 9 is about building 2 residential units on many lots where you used to only be able to build 1 unit.

The legislative counsel says that the first section “would require a proposed housing development containing no more than 2 residential units within a single-family residential zone to be considered ministerially, without discretionary review or hearing, if the proposed housing development meets certain requirements”

SB 9 offers a ministerial, non-discretionary permitting process - that means the planning staff can issue it without it going to the planning commission. You don’t need to go through processes that bog down a lot of housing projects like CEQA review and public notice.

It’s supposed to be as easy as the ADU permits, if you’re eligible.

Similar to the ADU laws, you mostly use the existing local code unless it would pre-empt you from building up to 800 sq ft with a 4 ft side and rear yard setback.

For example, you would follow the local guidelines for yard requirements and height requirements, unless those rules would prevent the construction of two 800 sq ft units on the lot.

The local jurisdiction can also require up to 1 parking space per unit unless the unit is located within half a mile of major transit, high quality bus service, or within a block of a car share.

If you’re replacing an existing non-conforming structure, you can generally maintain the existing footprint.

There are different rules for ADUs and SB9 approved units and we’ll write more about this as we learn more.

SB 9 Lot Split Explained

Summary: Many lots that are at least 2400 square feet, can now be split into 2 roughly equal lots that can be sold separately.

The second section of SB 9 is about splitting lots into 2 lots.

There are many restrictions covered later in the article, but if your lot is eligible then you can get a ministerially approved, non-discretionary permit to split your lot into two lots.

And you can sell those lots separately!

The lots have to be a roughly 50/50 split (you can go up to 40/60 split).

The lots both need to have access to the public right of way (ie you need to access the street!)

And neither lot can be smaller than 2400 sq. ft.

You cannot split a lot that has already been split with SB9 - no infinite splits!

And you cannot split a lot adjacent to a lot you already split (or somebody you’re working with has already split) so individuals won’t be able to split adjacent lots with SB9.

How many units can you build with SB9?

Summary: Basically 2 homes per lot. If you split a lot, then 4.

So if you can combine both of these sections, you can take a lot zoned for one single family residence… split it into two lots, and build two homes on each lot for a total of FOUR homes.

Accessory dwelling units and Junior accessory dwelling units count toward the unit total so no city will be required to allow more than 2 units per lot (or 4 units after a lot split.)

Note: a city or county can choose to allow for ADUs and JADUs on top of the SB9 law, but it is not required. So if the local jurisdiction wants to allow more units, that’s fine. But that was already true before the passage of SB9.

Who can use SB 9? And who cannot?

For the SB9 second unit:

You need an urban lot (as designated in the census)
Your lot needs to be SFZ
You can’t be in a historic district or on a historic registry or property
You can’t have an HOA that has practically prohibited the use of SB9
You can’t demolish or alter too much of the building if you are under an affordable housing covenant, rent control, or long term tenants
You can’t have used the Ellis Act in the past 15 years to evict a tenant
If you have a lot of fire or seismic risk (or some other risk) the city can block your project with a preponderance of evidence on the record
When counting how many units there are on a lot, ADUs and JADUs count toward the total units. So if you already have an ADU or JADU, then you are already at the limit for that lot

For the SB9 lot split:

All of the above… PLUS:
You have to sign an affidavit that says you plan to live in one of the units on those lots for the next 3 years
The resulting lots need to be >2400 sq ft each
The resulting lots need to both have access to the public right of way
You cannot split a lot that has already been split with SB9 - no infinite splits!
You cannot split adjacent lots

Some frequently asked questions about SB 9

How does SB9 affect property taxes?

Ultimately, you want to talk the county tax assessor about your specific project.

I’ve heard a couple different takes so far… which is never a good sign.

But generally speaking, the taxes aren’t reassessed on a lot unless there’s new ownership or new construction.

If you bought your land 30 years ago, that’s great news for you because you probably don’t want to reassess - if you bought your land yesterday, you might want to get the old lot reassessed because it’s smaller after a lot split (a downward reassessment).

For ADUs, the new building is usually assessed at the current value, but construction doesn’t trigger the reassessment of the existing home. That would be a good thing for second unit development under SB9 too.

Should I use an ADU or an SB9 Regular Dwelling Unit?

For our clients, we have some who will benefit from using ADU rules and others who will benefit from using regular dwelling unit rules. The answer to this question really depends on your project goals and your jurisdiction’s rules.

For example, if a client wants to build a two story home but their jurisdiction doesn’t allow ADUs to be greater than 16 feet in height, we might want to build a regular dwelling unit instead.

On the other hand, if a client is in an HOA that has prohibited the use of SB9 to make additional dwellings, they might want to build an ADU or JADU (using AB670).

The rules about each of these units are very different and can vary tremendously from one jurisdiction to the next. You should really work with a professional to get answers about your specific project.

Can you sell your ADU separately?

A lot of people are wondering if they can split a lost with an ADU on it and sell the ADU separately…

We’re asking the lawmakers for clarification about this. It will probably come down to local enforcement, in my opinion.

You will likely need to do a lot of work to separate some ADUs (eg utilities separation, new address) before it can be sold separately… if they even allow for that, since the ADU definition says pretty clearly that it can’t be conveyed separately.