AB 306 pauses most new state and local building-standard changes that apply to residential units for an 'intervening period' running from October 1, 2025, through June 1, 2031, while carving out a set of narrow exceptions (emergencies, home hardening, certain model-code incorporations, and a few administrative changes). The bill also directs the California Building Standards Commission (CBSC) to reject local modifications affecting residential units unless they fall within those exceptions and adds the International Wildland-Urban Interface Code to the list of recognized model codes.
The sponsor frames the pause as a supply-side intervention: reduce uncertainty and avoid incremental cost drivers that could slow housing production. Practically, the measure centralizes authority over emergency adjustments, tightens the circumstances under which charter cities and counties can adopt stricter residential standards, and creates a model-home grandfathering rule that binds future units built from an approved model design to the standards in effect when the model was approved.
At a Glance
What It Does
The bill bars cities, counties, and state adopting agencies from enacting or approving new building standards for residential units during the intervening period unless an enumerated exception applies (emergency standards, home hardening, specified model-code updates, errata, research-based standards, or preexisting local amendments). It also adds the International Wildland-Urban Interface Code to the statute’s model-code list and limits the kinds of changes the CBSC may make between triennial code editions.
Who It Affects
Local governments (including charter cities), the California Building Standards Commission, state adopting agencies (e.g., HCD, State Fire Marshal), residential developers and homebuilders, building officials, and code consultants. Fire protection districts and agencies that produce research-based or climate-related standards will also be affected by the narrowed pathways for adoption.
Why It Matters
The measure substitutes a temporary statewide freeze for the normal rolling update process, trading continued code evolution for regulatory predictability intended to lower the risk premium on housing projects. It therefore affects timelines, compliance planning, and product demand for anyone designing, approving, or building residential projects in California.
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What This Bill Actually Does
AB 306 creates a six-year ‘intervening period’ during which most new or more restrictive building standards that apply to residential units cannot be adopted at the local or state level. The ban applies to changes that a city or county would otherwise make under the State Housing Law and to standards state agencies would submit through the CBSC’s normal 18-month or triennial adoption cycles.
The statute does not eliminate all movement: it preserves emergency standards, rules tied to ‘home hardening,’ certain model-code incorporations and errata, research-derived standards, and administrative changes meeting narrow criteria.
For local governments the bill tightens Section 17958-family procedures. A city or county must either have the same modification already filed and in effect as of the cutoff date, or the change must fit an exception listed in the bill, or the CBSC will reject it.
The commission is empowered to reject local filings that don’t meet the standard and must review administrative-practice changes (those that affect permitting timelines, fee schedules, permitting software, internal operating costs, or enforcement program structure) within 45 days of receipt.At the state level, AB 306 prevents adopting agencies from submitting most residential standards for commission consideration during the intervening period, except for specified categories such as emergency updates, State Fire Marshal home-hardening proposals, model-code incorporations required for the triennial code, or standards tied to defined statutory research initiatives. The bill also amends the statutory definition of 'model code' to explicitly include the International Wildland-Urban Interface Code.The measure alters permit-level application rules: if a jurisdiction approves a model home design under the building standards in effect at the time a permit is filed, those standards must apply to all future dwellings based on that model design in the same jurisdiction unless the design substantially changes or ten years elapse.
Finally, the bill limits the kinds of interim changes the CBSC can make between full code editions to editorial clarifications, emergency standards, State Fire Marshal Chapter 7A/WUI amendments, errata to national model codes, and narrowly defined administrative updates.
The Five Things You Need to Know
AB 306 establishes an intervening period from October 1, 2025, through June 1, 2031, during which most new or more restrictive building standards that apply to residential units cannot be adopted by cities, counties, or state adopting agencies.
Exceptions to the moratorium include: standards the commission deems emergency standards for health and safety, standards related to 'home hardening' (including certain proposals from fire protection districts or the State Fire Marshal), incorporation of the latest model codes and errata, standards tied to specified statutory research, and certain preexisting local amendments filed and effective by the cutoff date.
The California Building Standards Commission must reject local modifications affecting residential units that do not meet an exception and must review administrative-practice changes (permitted categories) within 45 days of receipt.
A model-home grandfathering rule requires standards in effect when a model-home design’s permit was submitted to apply to all future dwellings based on that approved model in the same jurisdiction, unless the design substantially changes or ten years elapse.
The bill adds the International Wildland-Urban Interface Code to the statutory list of recognized model codes and narrows interim CBSC supplement changes to editorial fixes, emergencies, State Fire Marshal Chapter 7A/WUI amendments, errata, and a narrow set of administrative changes.
Section-by-Section Breakdown
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Findings: statewide housing crisis and scope claim
The Legislature frames the measure as a statewide response to housing scarcity and rising construction costs, and explicitly finds the subject matter to be of statewide concern so the restrictions apply to all cities, including charter cities. That framing is the bill’s constitutional anchor for preempting local action during the intervening period.
Local amendment moratorium for residential units
This is the core local-preemption provision: from the intervening period start date, cities and counties may not amend, add, or repeal provisions of the state-published building standards as they apply to residential units unless the change was already filed and in effect by the cutoff, is an emergency standard, relates to home hardening, implements an eligible general-plan–aligned mixed-fuel/amplified electrification incentive, or fits narrowly defined administrative-practice categories. The mechanics preserve the 180-day effective rule for published local amendments outside the moratorium.
Limits on local findings-based modifications
Normally local governments may adopt stricter standards as 'reasonably necessary' for climatic, geological, or topographical conditions. The bill suspends that authority for residential units during the intervening period unless an enumerated exception applies. That removes the usual path of local technical justification as a route to stricter residential standards for the duration.
Commission review and rejection power; 45-day admin-review timeline
The CBSC is directed to reject local modifications affecting residential units that fail to meet the bill’s exceptions. The statute also requires the commission to review the narrow category of administrative-practice changes within 45 days of filing, creating a firm—but limited—fast-track for certain permit/fee/IT/permitting-process reforms.
Model-code list expanded to include the Wildland-Urban Interface Code
The bill amends the definition of 'model code' to add the International Wildland-Urban Interface Code. That explicitly recognizes the IWUIC among the national model codes the state may incorporate and supports future WUI-focused references in state code actions.
State agency submissions and 18‑month cycle carve-outs
AB 306 suspends the CBSC’s standard 18-month adoption cycle for standards affecting residential units during the intervening period, preventing state adopting agencies from submitting most residential standards unless they fall into the enumerated exceptions (emergency/home-hardening/model-code incorporation/research-based items/specific statutory pathways). The bill preserves the CBSC’s established approval criteria and great-weight deference but narrows what can even be considered for residential units.
Model-home permit grandfathering
A jurisdiction must apply the state and local standards in effect when a model-home design’s permit was submitted to all subsequent dwellings based on that approved model in the same jurisdiction unless the model changes substantially or ten years pass. This creates a binding grandfathering rule intended to stabilize product lines and project economics for builders using model designs.
Limits on interim CBSC supplements and publication duties
Between triennial code editions the CBSC may publish supplements only for editorial/clarity fixes, emergency standards, State Fire Marshal Chapter 7A/WUI amendments, errata emergency updates to national model codes, and the specified administrative changes. The commission must also publish certain statutory notices within Title 24 and maintain availability obligations for state and local agencies.
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Explore Housing in Codify Search →Who Benefits and Who Bears the Cost
Every bill creates winners and losers. Here's who stands to gain and who bears the cost.
Who Benefits
- Residential developers and homebuilders — gain predictable regulatory baseline for up to six years, which reduces the risk that mid‑project code changes will increase costs or require redesign.
- Model-home and production-home manufacturers — benefit from the model‑home grandfathering rule that locks applicable standards for follow‑on units, supporting repeatability and inventory planning.
- Local permitting departments seeking operational modernization — receive a defined, expedited pathway (45‑day review) for administrative-practice reforms that reduce permitting time or costs.
- Fire protection districts and the State Fire Marshal — retain a clear channel to advance home‑hardening and WUI‑related standards despite the moratorium.
- Statewide housing planners and agencies pushing to accelerate housing production — get a temporary regulatory pause intended to remove one class of incremental cost drivers.
Who Bears the Cost
- Local governments — cede near‑term authority to adopt stricter residential standards and may be constrained in pursuing local climate, health, or safety innovations tailored to local conditions.
- Climate and energy policy advocates and municipalities pursuing rapid decarbonization — face delayed or blocked adoption of electrification, energy‑efficiency, and low‑carbon building standards for residential projects.
- Manufacturers and product innovators for emerging code‑driven technologies — may see demand deferred while new product‑enabling standards are frozen.
- The California Building Standards Commission and state adopting agencies — inherit added administrative burdens to evaluate exception requests, process 45‑day reviews, and defend rejections, potentially straining staff and legal resources.
- Homeowners and future occupants — could face safety or resiliency tradeoffs if postponing non‑emergency updates delays important but non‑emergency improvements (for example, incremental wildfire, seismic, or indoor‑air quality measures).
Key Issues
The Core Tension
The central dilemma is between short‑term regulatory certainty to lower housing production risk and the long‑term need to update building standards for safety, climate, and resilience; freezing standards helps developers plan but delays adoption of potentially necessary safety and decarbonization measures and shifts decision authority from local expertise to a narrow set of statewide exceptions.
AB 306 trades code evolution for regulatory certainty, but that exchange raises several implementation and policy questions. First, the legislation’s scope hinges on the phrase 'applicable to residential units'—the text does not define the outer boundary (mixed‑use buildings, accessory dwelling units, hotel‑to‑housing conversions, and projects with shared systems may trigger disputes about coverage).
Second, the bill repeatedly references a cutoff phrasing ('previously filed ... in effect as of January 1, September 30, 2025'), which appears inconsistent and could produce administrative confusion about which local amendments qualify as grandfathered. Clerical ambiguity like that will increase litigation and administrative appeals unless clarified.
The carveouts generate further tension. 'Home hardening' and emergency standards remain viable paths, but those terms are not tightly defined in the bill; parties will contest what interventions legitimately qualify—especially where a safety rationale overlaps with climate or electrification goals. The narrow list of allowable interim CBSC changes protects against unplanned cost drivers, yet it also means necessary technical updates to model codes or new research findings outside the listed exceptions will be delayed until 2032, risking a larger one‑time compliance burden later.
Finally, though the bill asserts no constitutional reimbursement due because local agencies can raise fees, the practical shift in regulatory authority could still produce unfunded costs for local enforcement and permit administration during the intervening period.
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