Despite objections from the Bath Preservation Trust, the practice secured the go-ahead from Bath and North East Somerset Council's planning committee to 'extensively modify' the ground and first floors, improve access and create a new entrance area to the existing riverside building.
The new scheme will involve the 're-clothing' of an electricity sub-station next to the office's main entrance with the addition of a contemporary circular enclosure formed from vertical timber fins.
Externally, a 'modest balcony' overlooking the River Avon is planned at first-floor level on the side of the former steam-powered flour mill, which was built in 1880 by architect Henry Williams and extended in 1892 by F W Gardiner.
Design Engine architect David Gausden said: 'We have designed the first-floor balcony, the part of the scheme that received the majority of objections, to echo the existing platforms projecting from the building.
'Historical records and photographs show that Camden Mill accommodated many more projecting platforms during its previous lives than those that currently remain.'
Work is expected to start shortly.