The FAST Housing Act directs the Department of Housing and Urban Development to create a demonstration program awarding up to 15 competitive grants to local governments and public housing agencies working to increase housing supply in areas experiencing workforce growth from federal infrastructure investments. Grant recipients must commit to zoning reforms that facilitate housing development, such as allowing mixed-use buildings, streamlining permitting, reducing parking requirements, and enabling manufactured housing, while prioritizing communities that have already successfully removed regulatory barriers. The program funds costs for converting commercial space, developing and rehabilitating workforce and affordable housing through public-private partnerships, technical assistance, and property acquisition, with at least 30 percent of units remaining affordable for households earning up to 80 percent of area median income. The bill finances this effort by repurposing 10 percent of unobligated COVID-19 relief funds and requires HUD to study the program's effectiveness within 18 months and annually thereafter, comparing approval timelines and housing production in participating and non-participating communities.