After especially large and destructive disasters, FEMA’s Building Science Branch may send a Mitigation Assessment Team (MAT) to review the damage patterns and to list possible changes in construction and regulations that could mitigate future losses.
To find tornado-related MAT reports, go to the FEMA Mitigation Assessment Team (MAT) Reports web page available at https://www.fema.gov/fema-mitigation-assessment-team-mat-reports and expand the Natural Disaster Reports and Presentations option.
Scroll down until you see the Tornadoes header. The publications listed have been developed by the Building Science Branch of FEMA's Federal Insurance and Mitigation Administration (FIMA). They cover natural and man-made disasters.