It will be used as a backstage green room and equipment store freeing up space in the hall, and incorporate much needed extra toilet facilities.
Town councillor Steve Hurrell, chair of the Lansdown Hall Working Group, said there had been some disruption.
He said: “To prepare the ground for the new extension to Lansdown Hall specialist contractors brought their piling equipment into Bank Gardens. Unfortunately one machine accidentally caught one of the gates attached to the stone pillars causing the pillar to be damaged.
But the town council is very pleased to have found a swift resolution. It has been agreed that the stonemason who rebuilt the gateway in 2014, will be able to fully reinstate the pillar and the gate – at no cost to the town council. We hope work will start in the week beginning 23rd February.
“We are very sorry for any disruption this may have caused.”
The town council bought Lansdown Hall in 2010 to save it from closure. It is run by a charitable trust and provides a community space for the town. Work is due to be completed in the spring.