An ADU adds a second, smaller home on your existing lot without changing ownership, while SB 9 lets you split the lot into two parcels and build up to two units on each. ADUs are simpler and cheaper; SB 9 offers more units and the option to sell parcels separately. Here’s how ADUs and SB 9 compare.
A lot of people are excited about the prospect of adding a second home to their property using the new California SB9 law. There are two portions to the SB9 law: 1) the urban lot split and 2) the two-unit development. Lets compare building a second home using the SB9 two-unit development regulations versus the original ADU regulations from a few years back.
Here at GreatBuildz, a free service that connects homeowners in the Bay Area, Los Angeles, Orange, San Diego and Ventura Counties with reliable ADU contractors, we speak to homeowners every day about comparing ADU vs SB9 regulations – read on to learn more.
SB9 vs ADU Guidelines
In both cases you can build a second home on a property which has an existing single family home. And there are other similarities. In both cases, you can build your second unit either attached or detached from the main home. Both regulations allow you to build your new unit with only 4 foot setbacks from your back and side property lines. Also, the parking requirements are similar: one parking spot is required unless your property is no more than ½ mile from any public transit stop.
Now lets discuss the differences. With regard to the size you can build – ADU guidelines allow you to build up to 1200 sf, but this may be limited by what is allowed by FAR – the floor-area-ratio under your property’s zoning. But in all cases, you are allowed to build up to 800sf regardless of the FAR limitations.
With an SB-9 second unit, there is no limitation to the size of the home you can build, but again, you must abide by your property zoning FAR limitations. And similarly, the SB9 ordinance allows you to build up to 800sf in all cases, regardless of FAR limitations.
The state’s ADU laws preclude cities from charging you expensive impact fees for any ADU under 750sf. But, there is no such prohibition for an SB9 unit, so you may have to spend thousands more on things like school fees, park fees, sewer and water fees, etc.
One other thing to consider. If you build an ADU on your single-family property, you cannot build another ADU on that same property…only one is allowed. The exception is that you CAN build a Junior-ADU.
However, with SB9, you can build a second home on your property AND then also build an ADU…either at the same time or at a later time. Although most people aren’t planning on building more than one additional unit at their property, its something to consider.
I would say there are more similarities than differences with regard to the SB9 two-unit development and the ADU guidelines in California. If you want to build a second home on your property and need to decide between these two options, you should do a couple of things. First, check the website of your City’s planning department for any specifics requirements they may have. And you should speak with a local architect because they are well versed in these various rules and can guide you to the best decision for your specific property.
Check out this GreatBuildz ADU project in Newbury Park
Other specific limitations in SB9 vs ADU regulations:
Senate Bill 9 (SB 9) applies only to single-family residential zones, whereas ADUs can be built in both single-family and multifamily zones. Since SB 9 is new, ADUs benefit from a streamlined permit process, which can lead to faster approvals. Some cities have enacted limiting ordinances for SB 9, and unlike with ADUs, the state has not passed more legislation to address these local restrictions.
Properties in high-risk areas like fire zones, earthquake zones, historic zones, and floodplains are ineligible for SB9 development. SB9 housing cannot involve the demolition or alteration of housing that currently has or had a tenant in the past three years.
Can I Use Both SB9 and ADU rules to maximize my property?
One interesting and important thing to note about the SB-9 regulations is that they do not preclude building one or more ADU’s on your property.
If you have an existing single family home on your property, you can add a 2nd home unit under SB-9 guidelines AND you can also build an ADU on the same property as well as a junior ADU. So when you layer these guidelines you can have 3 or even 4 units on your property. So let me give you a few examples.
- Here’s a lot with an example of a second home added per the SB9 guideline plus a detached ADU. Notice both of the new units we’re added to the backyard of the original home.
- Here’s an example of an SB9 unit that’s build attached to the original home essentially forming a duplex plus one ADU built in the backyard. Because most existing single family homes aren’t situated with enough room to add another home next to it, a more likely scenario would have the SB9 unit attached at the rear of the existing home.
- In this scenario, an SB9 home is added in the rear yard of the existing property and a Junior ADU is created from the existing garage or other portion of the main house. A Junior ADU is limited in size to 500sf or less.
- In this image, it shows a scenario where an SB9 unit is attached to create a duplex and two new ADUs are also built in the backyard. Although this is probably an unlikely scenario unless you have a very large lot, it does show that three new units could hypothetically be built on a lot in addition to the original single family home. The SB9 ordinance does cap the number of total units on a lot for four.
Again, you should note that, in most cases, even if your property’s zoning doesn’t allow for any more building per the FAR maximums, you should be allowed to build an 800sf (max) SB9 unit AND an 800sf (max) ADU.
How to Decide Between SB9 vs ADU for my project?
The bottom line is this. If you simply want to build a second unit/home on your property under 1200sf, you should use the ADU regulations. It will make the planning and permitting process simpler and quicker. And it will likely be cheaper because the city impact fees might be lower. And most cities & architects are very comfortable working with ADU projects since they’ve been legal for some time and many thousands have already been built.
However, if you want to build a second home larger than 1200sf, your only option is to use the SB9 regulations (assuming your property zoning allows for this FAR). Alternatively, if you want to maximize your lot by building multiple units, you might attempt to use both SB9 and ADU regulations as I described above to get 3-4 units (main home, SB9, ADU, JADU).
Using SB9 to build your project will certainly complicate things, so only use these regulations if you absolutely need to for your project.
Frequently Asked Questions
What is the difference between an ADU and SB 9?
An ADU is a secondary unit added to your existing single-family lot, keeping one parcel and one owner. SB 9 lets you split the lot into two parcels and build up to two units on each, for as many as four homes. ADUs are simpler and cheaper; SB 9 allows more units and selling parcels separately.
Is an ADU or SB 9 better for my property?
It depends on your goals. An ADU is faster, cheaper, and ideal for rental income or family space. SB 9 suits homeowners who want to split the lot, build more units, or eventually sell a parcel. SB 9 is more complex and, for lot splits, requires you to live on-site for three years.
Can you combine an ADU and SB 9?
The rules interact and vary by city, and combining them can be limited, since SB 9 lots have their own unit caps. Some homeowners build under one path or the other rather than stacking both. Check with your local planning department, as local ordinances shape what’s allowed on your lot.
And if you want to make the process even easier, you can contact GreatBuildz who can match you with great ADU contractors who have already been thoroughly screened and vetted.
Just reach out to us to be personally matched with three of our trusted, pre-vetted contractors in the Bay Area and Southern California areas. Contact GreatBuildz today at 818.317.3567 or visit our website for more information.
