There is a great deal we know about how to improve the efficiencies and effectiveness of building operations, but there is also a great deal we don't know. And many inspirational green building success stories are just that: inspirational stories. For green building and energy efficiency to be incorporated at a transformational scale across all building types, we need replicable models and more hard numbers to go along with the incredible stories. And the affordable housing finance community is well placed to address this need.

A number of existing programs exist to capture project data at a reasonable scale over time. Since 2007, the Department of Housing and Urban Development's Office of Affordable Housing Preservation has been capturing data on utility use and indoor air quality for a subset of privately owned assisted housing through the Mark to Market program, covering more than 10,000 units per year. The Environmental Protection Agency (EPA) also recently expanded its Energy Star Portfolio Manager program to include multifamily, with approximately 1,000 projects enrolled to date.

Beyond the federal government, Massachusetts-based New Ecology has developed a Web-based data collection and reporting tool that is built specifi- cally to compare projects in a portfolio to each other as well as to an overall average of similar buildings in the database.

Stewards of Affordable Housing for the Future (SAHF) under a grant provided by the MacArthur Foundation retained Bright Power, a New York-based energy consulting firm, to collect projectlevel utility data for 650 projects containing 40,000 units owned by eight of its members. This has led to the creation of an online utility management tool that allows SAHF's members to benchmark utility usage and cost as well as to compare performance of properties.

Unfortunately, data collection itself is not enough to transform the market for green building. Data must also be compared with a benchmark of some kind, taking into account project type, age, location, and other factors—it is not simply a tool for measuring success after a building retrofit. For affordable housing owners thinking about a green building retrofit, a good first step is to gather the previous 12 months of project data to assess which projects are consistently underperforming and where to prioritize investments. The EPA Portfolio Manager and the New Ecology tools are designed precisely for this kind of analysis.

To be useful to the affordable housing industry, utility use and project data that are collected must be commensurable with data collected from other projects. These data would need to be made accessible to public agencies and academic researchers, while addressing concerns about individual privacy. And unit-level data should be collected, compiled, and shared with residents to empower them to make better choices, even when they are not paying directly for certain uses.

One reason to gather and analyze all this data is to strengthen project underwriting for institutional lenders, private investors, and public agencies. The affordable housing financial industry, in particular, is well-positioned to collect accurate and consistent data over time and at a large scale. For institutional lenders and private investors, this data could then be compared across a very large portfolio to develop strong baselines, quantify individual successes, and possibly create new products. For public agencies, this data could be analyzed to refine utility allowances, measure taxpayer savings, and support additional research and innovation.

The greatest potential benefits are to those entities for whom affordable housing is a direct investment, whether of private dollars or public resources. As such, the push for data collection, as well as some of the funding necessary, should come from the larger players. The result will be more inspirational stories to tell policymakers about individual projects and the families who live in them.

Casius Pealer is director of the Affordable Housing Initiative at the U.S. Green Building Council, where he focuses on advocacy and public policy.