The firm wants to expand the shopping area by a quarter, build a bigger restaurant and move the entrance, toilets and cash machines.
"The store is a reasonable age and trades very well," said Mark Graver, from Sainsbury's.
"But this is about making it more comfortable for existing customers and encouraging growth."
The company wants to extend the store towards Albion Street - and is now waiting for planning permission.
"I would expect between 20 and 30 new jobs but that will not be confirmed yet," added Mr Graver.
Converted for the new archive on 13 March 2001. Some images and formatting may have been lost in the conversion.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article