This terrace house in London's Marylebone district once belonged to a product design guru from the 1970s but it had seen better days. Set within the Dorset Square conservation area the external form and materials of the building could not be changed, but the interior construction had to be completely demolished and rebuilt. We used a combination of conservation and contemporary construction techniques to recreate the house with exceptional environmental performance allowing sustainable living in with no compromise in comfort. The butterfly roof form was retained but a new roof structure allowed it to be revealed inside providing character and much needed additional volume, light and air. In turn, this allowed an adjustment of the the first floor level which gave the downstairs and upstairs rooms a much better proportion. The canvas for an an elegant interior design was set. Central to the success of the design is the tiny external courtyard – priceless in this dense central location. Treating the courtyard as an external room, or an extension of the open plan living space, suggested a movable glass screen that when opened blurred the boundary between inside and out. There is a monochromatic theme to the finishes; black and white on the ground floor and pure white upstairs save for the showeroom which is darker more intimate. This is followed through to the bespoke furniture and joinery items in various shades of white. The resulting house is light and airy, and feels much bigger than it actually is..