Infill development is increasingly the best — or only — option for landlocked and built-out cities to add housing. However, estimating where and how much infill housing could realistically be developed are challenges. Many city planners identify vacant lots but cannot say with certainty that the lots will be developed. And the definition of "underutilized" varies from expert to expert. As a result of the imprecision and varying approaches, the state Department of Housing and Community Development (HCD) is hesitant to credit cities for infill estimates in their housing elements. Without those potential infill units, some cities have a great deal of trouble documenting that they can accommodate their fair share of regional housing. To tackle this problem, Solimar is working with the non-profit group Environment Now and the City of Los Angeles to develop a standard methodology that estimates realistic infill housing potential well enough to count towards meeting state-mandated Regional Housing Needs Allocation (RHNA) targets. Our goal is to distribute the methodology to cities and counties so that local governments may receive more credit for feasible and likely infill housing development in future rounds of housing element updates. Our methodology, which is still evolving, starts with local planners designating infill study areas (ISA). These are census-block-based neighborhood areas with similar zoning and common housing ages and types. Planners characterize the ISAs based on 11 criteria (see chart) leading to a series of ISA types, such as "postwar, low-density, single-family development with poor transit access," or "commercial and small apartments along transit arterials." Each infill study area's current and potential housing are calculated using Census 2000 housing counts, post-Census permit records, and zoning. The next step is to apply quantifiable and feasible infill strategies targeted to ISA types, while still reflecting zoning. This is where the City of Los Angeles comes in. We are developing and testing infill strategies on 519 ISAs identified by Los Angeles city planners earlier this year. Strategies being developed are aimed at both market-driven situations and those needing government action such as a change in design standards. The strategies do not necessarily include changing zoning or subsidized development. The strategies that are most quantifiable and financially feasible are being "formulized" by Economic Research Associates so that the strategies translate into identifiable increases in housing densities. The idea is that a planner in any urban city or county could apply a strategy to target ISA acreage, and the formula would produce a theoretical increase in housing units. In reviewing housing elements, HCD would then credit cities and counties for some or all of the estimated infill housing identified by this methodology. Cities and counties would need to monitor the success of the strategies and report on their success. The methodology will be relatively inexpensive and easy to use with a companion manual and sample documents. The process could be done without a geographic information system (GIS) in small cities, but the methodology is designed for a GIS system based on ArcView 3.3, an Access database, TIGER census files, and typical building permit databases. The methodology could be combined with other planning efforts, such as brownfield reuse, vacant lot inventories, and redevelopment. The methodology is still evolving, but it is promising and should help cities and counties realistically estimate infill housing enabled by specific government actions and housing that should occur as a result of market-driven activity. The main goal is to get local planners, state housing officials and developers all on the same page.