Questions have been raised about the safety of the renovation work taking place in Dewsbury Town Hall.
The first phase of a partial internal refurbishment got under way in May.
It includes the creation of a new ceremony room for the register office, a new box office and reception, and a new community exhibition space.
But councillors heard it had also caused a structural fault in the listed building.
Coun Andrew Pinnock (Lib Dem, Cleckheaton) told a full council meeting: “During recent building works at Dewsbury Town Hall I am told that supporting pillars were removed resulting in a serious structural fault in offices on the floors above.
“This was a potentially life threatening situation.”
He asked the Cabinet to explain the incident.
Cabinet member Coun Shabir Pandor (Lab, Batley West) said: “This incident that occurred was serious and unfortunate but there was never any risk to life or limb.”
He said part of the work involved straightening a beam.
“When we moved the two pillars that are holding the original beam up, a crack appeared,” he said.
“The new supports have been installed and the crack has been made good.”
He said there had been no other incidents.
Meanwhile, an unpleasant smell in the ground floor of the building was a talking point at Dewsbury Chamber of Trade’s latest meeting.
Dudley Ward said: “It’s unbelievable. It’s coming from the sewers in the basement.
“They’ve been looking into it for some time.”
A council spokeswoman said: “There is a sporadic drain smell at Dewsbury Town Hall which doesn’t appear to follow any particular pattern. As with any buildings of this age that have had various stages of development problems like this are difficult to trace.
“We’ve done a survey and we have some work to undertake internally as part of the scheme which we hope will resolve the problem, but there may be further work to be undertaken externally with Yorkshire Water as the main drainage may be a contributory factor under certain conditions. This needs further investigation.”
The renovation is due to be completed next month.