Demolition of the eastern part of Crawley Town Hall has been delayed until October 2019.
It was originally hoped to take place this year so that regeneration work, including 273 new homes, could begin.
The change has been made to reduce financial risk and take account of delays due to investigations into potential listing, said the council.
Councillor Andrew Skudder, Cabinet member for Resources at Crawley Borough Council, said: “Delays to the programme, caused by the listing investigation, pushed back the dates for putting work to tender.
“We have a duty to manage all risks around the programme of works, and commencing demolition of part of the Town Hall before all tenders are received would have been an unnecessary risk.
“This is why we won’t be demolishing the building until next October.”
The demolition at the eastern end of The Boulevard will make way for a nine-storey building housing the new Town Hall and commercial office space.
There will also be 273 flats, a public square and a new heating system.
A council spokesman said: “This provides the council with the opportunity to bring the Council Chamber and Civic Hall back into use until June/July 2019, when decommissioning will commence.
“The detailed design work for the building and interiors will continue as planned through the remainder of this year ready to tender for the construction contract early next year.”
The new Town Hall is expected to be completed in summer 2021.