The structure like a pipechase built on to the gable contains the extended chimney flues from the lower building let into the wall of the taller one.
This allows smoke from the house fires to be drawn up to the chimney head above, keeping it away from the windows of its higher neighbour.
Note the white tramcar in the background near the Townhouse.
Prior to 1935, up to the advent of the Cornonation and Cunarder Trams, routes were colour coded. Standard vehicles had a broad band painted all round between the decks in blue, green, yellow, red or white, so that all cars on a particular route had the same colour.
This allowed intending passengers to pick out a vehicle from a distance that was on the service they were waiting for.
This was particularly useful in busy areas with them running close together an the destination screens hard to see, and where there could be up to eight services.