The document summarizes the development of the Housing Insights tool in Washington DC, which was created through a partnership between local government, non-profits, and civic technologists. The tool combines housing and neighborhood data to help stakeholders identify affordable housing units at risk of being lost and target preservation efforts. A paid project manager oversaw over 100 volunteers who contributed over 2,200 hours to build the open source tool. User feedback was incorporated throughout the process. The tool and partnership provide a model for collaboratively addressing policy issues through data and technology.