The 16-strong office said it was determined to expand its workload outside its northern base following the acquisition of the London firm, owned by Ralph Cooley.
Ramsden Barrett was set up in 1989 and after a short period working on housing association schemes it moved into the commercial sector.
Founding partner Patrick Barrett said that the office decided on the takeover after it became clear that it was increasingly winning work in the South East.
'We did not want a postal address in London and nothing else, like a lot of practices do,' he said. 'We wanted a proper office doing real work.
'This expansion is a strategic coup for us. It brings us closer to our increasing client base in commercial and retail sectors in the south. At the same time it offers further scope to build on Tread Architecture's expertise in the large top-end residential market,' he added.