“The Buffer” is not an actual legal requirement
While often cited by proponents of Measure K as a requirement, a "buffer" of surplus sites is not an explicit legal mandate under California's Housing Element Law.
The law does not contain any statute compelling a jurisdiction to identify sites for more than 100% of its Regional Housing Needs Allocation (RHNA). Instead, the "buffer" is an administrative recommendation from the Department of Housing and Community Development (HCD) and a "best practice" adopted by many cities as a "safe harbor" to ensure compliance with a separate, related law.
The actual legal requirement is found in Government Code § 65863, the "No Net Loss Law." This law states that a jurisdiction must maintain sufficient sites to meet its RHNA at all times:
The Law Requires Sufficiency, Not a Surplus: The law requires a jurisdiction to demonstrate an inventory of sites with "realistic capacity" to accommodate its RHNA. It does not legally require that inventory to exceed the RHNA. A jurisdiction with a highly accurate and defensible realistic capacity analysis that perfectly matches its RHNA number is, by definition, legally compliant.
A "Buffer" is a Tool, Not a Mandate: The 15-30% buffer is a recommendation from HCD, not a statute. HCD encourages it because it provides a simple, upfront way for a jurisdiction to protect itself from violating the No Net Loss Law. It is an insurance policy, not a legal obligation.
The "No Net Loss Law" Provides a Cure: The No Net Loss Law itself provides a legal remedy for when a jurisdiction's inventory falls below its RHNA. If a city approves a project at a lower density than planned, it creates a shortfall. The law explicitly gives the city 180 days to identify and rezone a new, equivalent site to "cure" the deficit.
Therefore, the legal requirement is not to have a pre-existing buffer, but to have the willingness and ability to rezone land quickly if a shortfall occurs.
"Realistic Capacity" is the True Standard: The core legal test from HCD is whether a jurisdiction's site inventory is "realistic." HCD's review focuses on challenging assumptions (e.g., that 100% of a site will be built out). If a city provides strong, evidence-based analysis that its sites will realistically yield its RHNA number, it has met the statutory standard. HCD may "encourage" a buffer during this review, but its legal finding must be based on the realism of the plan, not the size of its surplus.
In summary, a jurisdiction is not legally required to provide a buffer. It is only required to have a compliant, certified Housing Element and to maintain "no net loss" of capacity. A city can legally choose to meet this standard by demonstrating its inventory is sufficient (with no buffer) and committing to using the 180-day rezoning process to cure any shortfalls that may arise during the 8-year planning period.
