Cardiff Council has explained that the entire roof of the hall needs replacing. This repair could take about 18 months to finish.
The UK has seen many public buildings, like hospitals and schools, dealing with problems caused by reinforced autoclaved aerated concrete (RAAC) recently.
The Health and Safety Executive (HSE) warns that this building material is no longer safe because it can collapse suddenly.
Experts have been inspecting St David's Hall for the last few weeks after they found RAAC panels. Many of these panels are either «red — critical» or «red — high risk,» according to a report from the council.
Engineers say the venue should remain closed until they can either make some temporary safety changes quickly or replace the whole roof.
The council says making these changes would take at least six months and cost millions.
Even with these temporary changes, the roof still needs replacing. The council's cabinet now suggests doing it all at once.
Various performers were planning to have shows at St David's Hall in the next few months, including Strictly Come Dancing stars, singer Sophie Ellis-Bextor, writer Grayson Perry, and bands Wet Wet Wet and Go West.
The council was going to lease the hall to AMG, and AMG plans to reopen the venue well before the BBC Cardiff Singer of the World competition in summer 2025.