Design and Construction Report staff writer
Investigators with the National Institute of Standards and Technology (NIST) say the 2021 partial collapse of Champlain Towers South likely began in the building’s pool deck rather than the tower itself, and that warning signs of structural distress were visible in the weeks before the tragedy.
Investigative lead Judith Mitrani-Reiser and co-lead Glenn Bell presented an update on the investigation during a virtual meeting of the National Construction Safety Team (NCST) Advisory Committee on Sept. 9. The presentation summarized the team’s activities, preliminary findings shared in previous updates, and highlighted significant progress in analyzing the building’s failure.
Click this link to watch the presentation.
Bell said computer simulations and physical testing indicate the collapse likely started at a pool deck slab-column connection, with corrosion of steel reinforcement, concrete shrinkage, and improperly built construction joints contributing to the failure. Video and structural evidence show how the collapse progressed from the pool deck into the tower.
Mitrani-Reiser noted several advance indicators of the building’s distress, including a sliding glass door that came off its frame, horizontal cracking in a planter wall, shifting of a gate that caused it to jam, and water leakage in the garage area. Many of these signs were concentrated in the pool deck and street-level parking deck, which began collapsing at least seven minutes before the tower fell.
“The flow of water dramatically increased in the hours before the collapse,” she said, emphasizing that these warning signs were localized but significant.
The investigation team is aiming to complete its technical work by the end of 2025 and will produce a summary report along with six subject-focused technical reports. The team is also consulting with stakeholders across building design, construction, inspection, and maintenance to develop technical and policy recommendations to improve building safety.
“This tragic event has revealed flaws in our systems, and quality is at the heart of it,” Mitrani-Reiser said.
The next detailed public update from the Champlain Towers South investigation is expected in Spring 2026.
