Housing laws

Building more housing: SB 9 & density bonus

State laws that let owners and builders add homes, and how the City of San Luis Obispo and SLO County apply them.

By Jon, editor & creative director · Last reviewed October 8, 2026

Lot splits and two units (SB 9)

Many lots in single-family zones can be split into two, with neither smaller than 40% of the original and both at least 1,200 square feet (Government Code 66411.7).
The owner must sign an affidavit that they intend to live in one of the units for at least three years. New units can't be rented for 30 days or less.
A split can't require demolishing affordable or rent-controlled housing, or housing a tenant has lived in during the past three years.
Cities must decide applications ministerially (no hearing) within 60 days of a complete application, can require at most 4-foot side and rear setbacks for new structures, and can't impose standards that block two units of at least 800 square feet.
City of SLO: the 2026 housing rules update increased the number of residential lots that can be split under state law. Unincorporated county: the County streamlined SB 9 permits in 2025 (County of SLO).

ADUs

Backyard cottages and garage conversions have their own guide: Building an ADU in San Luis Obispo. In unincorporated SLO County, the County allows up to three ADUs per primary residence as of July 3, 2025 (County of SLO).

Density bonus

State density bonus law lets apartment and condo projects build more units than zoning normally allows if some are affordable.

To qualify: for example, 10% of units for lower-income households, 5% for very low income, or 10% moderate-income for-sale units.
What it earns: more affordability earns more bonus units and up to five incentives or concessions (such as relief from a height or setback standard), plus lower parking requirements.
Fully affordable projects get an 80% bonus, and near a major transit stop they can have no density cap and extra height.

Questions people ask

Can I split my lot in San Luis Obispo under SB 9?

Many single-family lots can be split into two under state law, with both lots at least 1,200 square feet and neither smaller than 40% of the original. The owner must sign an affidavit that they intend to live in one unit for three years. The City expanded the number of eligible lots in its 2026 housing rules update. Check your lot with City Planning.

How many ADUs can I build in unincorporated SLO County?

Up to three accessory dwelling units per primary residence, under County ordinance updates effective July 3, 2025.

Official sources

General information, not legal advice. Laws and local rules change, and exemptions depend on the facts. For a specific situation, check the source or talk to a California-licensed attorney. Tenants and landlords can also use the California Courts eviction & housing self-help guide. Last reviewed October 8, 2026.