This legislation aims to streamline the development of infill housing by exempting associated federal actions from certain environmental review requirements. Specifically, it stipulates that actions by a federal agency related to an infill housing activity will not be considered a major federal action under the National Environmental Policy Act of 1969, thereby bypassing the need for detailed environmental impact statements. The bill provides a precise definition for "infill housing," requiring it to be on vacant or underutilized sites not exceeding 20 acres, previously developed with an urban use, and largely surrounded by existing urban development. Crucially, such sites must undergo environmental assessments to confirm the absence of un-remediated hazardous substances and cannot be located in areas designated as high or relatively high risk for wildfire, coastal flooding, or riverine flooding by the Federal Emergency Management Agency's National Risk Index. The scope of "infill housing activity" includes land acquisition, demolition (excluding historic structures), construction, and conversion of non-residential buildings. Furthermore, to ensure the accuracy of risk assessments used in these definitions, the bill amends the Robert T. Stafford Disaster Relief and Emergency Assistance Act. This amendment mandates that the National Risk Index be updated every three years, rather than the current five-year cycle, providing more current data for development decisions.