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SB 9 and housing density

Updated: Mar 11

For our local builders and developers, SB 9 (aka 'the duplex bill') dramatically changes the way we look at Single-Family zoned residential lots and Housing Density in California.

In this post we're going to cover the following topics concerning SB 9:

1. What it is and how/when it came to be.

2. SB9's potential impact on local communities.

3. How SB 9 could be implemented.

4. What would prevent a site from being used for SB-9 housing

Multifamily residential infill project in Redding, California

While this bill passed back in 2021, we haven't heard much about it up here in the North State. Construction is a slow enterprise, and with the economy being so unpredictable the last few years, it may take a little while before SB 9 really starts to make visible changes in our communities - but it is coming. We say this because we are just now seeing the rush on ADUs in our communities based on the laws passed back in 2016 that overruled many of the local zoning codes that made them difficult to build. Since 2016 many cities and other jurisdictions across the state have gone as far as generating pre-approved ADUs for their citizens so the average homeowner could skip the design and permitting process altogether. Redding and Shasta County are two such jurisdictions, with Shasta Lake City showing interest in starting a program as well.

Now, we have a good number of local small-scale real estate developers working in and around our existing neighborhoods. Driving around town, you can see that these local developers are generally a great asset to our city - focusing on cleaning up neglected rentals and drug houses, infilling vacant lots, and stabilizing home prices in our older neighborhoods that are in need of a little TLC. We don't see a whole lot of overbuilt homes in older, smaller housing tracts or mismatches in housing density as local developers tend to be respectful of the neighborhoods where they may live as well. With the widespread adoption of the ADU laws, we are starting to see the developers, and average homeowners, building ADUs in the backyards of these project homes to add value and potential rental income - again, this doesn't really change the way our neighborhoods feel as ADUs are typically in back yards and not noticeable unless you're looking for one. However, SB 9 will allow these local developers to level up their projects once again, but this time, it will likely change the fabric and feel of our communities, and not everyone will be a fan.

What is SB 9?

Some could say that SB 9 effectively eradicated single-family zoning. Similar to the 2016 laws passed for Accessory Dwelling Units (ADUs), SB 9 overrides existing housing density limits in single-family zones. The bill is intended to support an increased supply of starter, modestly priced homes by encouraging the building of smaller houses on existing lots. If we look at many of our older neighborhoods around Redding, the lots can be quite generous, especially those neighborhoods with alleyways hiding between the streets like the Garden Tract or the Magnolia neighborhood. Objectively speaking, there is plenty of room for additional housing on these lots, but due to existing zoning ordinances, up until 2016, it was only possible to build an ADU if your lot met very specific criteria, and second homes were outright prohibited. Post 2016's ADU laws, ADUs were now permitted by right on almost all residential lots, meaning single-family lots now became 2-unit or potentially 2-family lots. Now, with SB 9, housing density effectively doubles, meaning those large lots may be split (even where zoning requires larger lot sizes) and each of those parcels can have a home and an ADU, and in some cases, the new lot can skip the ADU and just build a duplex or 2 homes.

What is SB9's potential impact on communities?

While it will be a few years before we really start to see our communities change due to this bill, they will potentially be unrecognizable in a couple of decades. This bill serves to encourage significant housing density increases, which we will see most dramatically in our older and more central neighborhoods, where the land itself is more valuable. Lots of a good size with small or dilapidated homes may be leveled to make way for four completely new units to avoid the added setbacks and complications of infilling around an existing building. Smaller lots may have multi-story homes squeezed together as well. Largely, we will see rapidly diminishing yards and a lot more people. While many homeowners may be quite concerned about this, there is one stipulation written into the bill that is intended to prevent this from being used by large-scale developers en mass: the applicant (homeowner/developer) must live on the property for 3 years.

  • HOAs may restrict the use of SB 9

  • Agencies may require up to (1) parking space per unit unless the project is within a 1/2 mile of a major transit stop or corridor

  • New SB 9 units may not be used for short-term rentals (Airbnb)

  • The SB 9 applicant (builder/developer/homeowner) MUST sign an affidavit stating they intend to live in one of the units for 3 or more years (unless the applicant is a land trust or a qualified non-profit).

How SB 9 is implemented:

SB 9 can be used to do the following:

  • Add new homes to the existing parcel

  • Divide the existing house into multiple units

  • Divide the parcel and add homes

The Associations of Bay Area Governments put together the following graphic table to help explain how the bill could be applied to a lot:

What this means:

  1. You can now build (2) homes on any parcel zoned single-family. Where an ADU is generally capped at 1,000-1,200 sf, there is no cap listed on sizes for single-family homes. Also, each of those homes may also have its own ADU. No property line adjustment is required for this.

  2. You can now divide any single-family zoned parcel into (2) separate parcels that can be smaller than the existing zoning ordinance-listed minimum lot size, but no smaller than 1,200sf each.

  3. All Rear and Side setbacks are effectively 4', and a project cannot be denied if it is the conversion of an existing building that does not conform to the 4' setback minimum.

  4. Between-building setbacks are reduced to building code minimums. For example, the city of Redding requires 10' between 1-story buildings and 15' between 2-story buildings while the building code only requires about 5' depending on the circumstances. So these new units can be quite close together.

  5. Agencies may still require access to the public way on new lots.

  6. Agencies cannot require you to correct non-conforming zoning issues with an SB 9 project

Which effectively means you can now build (4) units on what was a (1) unit lot. These units can be a combination of single-family homes, duplexes, and homes with ADUs or JADUS.

What would prevent a lot from being eligible for SB-9 housing?

  1. Anti-Displacement Measures - A site is not eligible for a proposed housing development or lot split if the project would require demolition or alteration of any of the following types of housing:

    1. Housing that is subject to a recorded covenant, ordinance, or law that restricts rents to levels affordable to persons and families of moderate, low, or very low income.

    2. Housing that is subject to any form of rent or price control through a public entity’s valid exercise of its police power.

    3. Housing that has been occupied by a tenant in the last three years.

  2. Environmentally Sensitive Sites - This list is fairly extensive, but most applicable in our area will be farmland, fire hazard areas, earthquake hazard areas, and flood risk areas. Yes, you read that right, WUI sites (Wildland Urban Interface, aka Very High Fire Severity Zones) are not necessarily candidates for SB-9 housing. However, talk to your AHJ about how this will be enforced.

  3. The lot has already been subdivided with a similar intent, or an adjacent lot has been split by the same property owner, or a person working in concert with that same property owner.

This bill went into effect on January 1, 2022.



Accessory Dwelling Unit (ADU) - An attached or detached residential dwelling unit that provides complete independent living facilities for one or more persons and is located on a lot with a proposed or existing primary residence. Accessory dwelling units shall include permanent provisions for living, sleeping, eating, cooking, and sanitation on the same parcel as the single-family or multifamily dwelling is or will be situated.

Junior Accessory Dwelling Unit (JADU) - A dwelling unit of no more than 500 square feet that are typically bedrooms in a single-family home that have an entrance into the unit from the main home and an entrance to the outside from the JADU. The JADU must have cooking facilities, including a sink, but is not required to have a private bathroom.

Single Family Zone - Usually abbreviated 'RS' on Zoning maps

Zone - The zone map divides a jurisdiction (city, county, etc.) into areas where specific types of development are allowed outright, allowed by permit, or restricted. Zones vary widely, but common zones include R (residential), C (Commercial), I (Industrial), MU (Mixed Use), and many variations and extensions thereof.

Zoning Ordinance - The local codes, maps, and laws that govern how development occurs in a given jurisdiction (County, city, etc.). Most zoning ordinances can be easily browsed through third-party websites like Municode, although updates may be a bit slow.

Jurisdiction - An area of land governed by a particular agency - for example, if you are building in the Redding area, you need to know whether your parcel falls under Shasta County's jurisdiction or the City of Redding's jurisdiction, and sometimes it can be both.

Housing Density - The number of individual housing units per acre. This is usually part of the zoning code, for example, RS-3 would be Residential, Single-family at 3 units per acre.

Property Line Adjustment (PLA) - A permit through the Planning Department that changes (moves, removes, or adds) a lot line on your property.


Links & References:

CA's website for SB-9 Information:

City of Redding Zoning Map (use the layers option in the top right-hand corner to show zones by color) -

Governor's Office Press Release on SB 9 -


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