A low-carbon retrofit of an existing commercial building in a central London conservation area receives a new high-quality facade. A collaborative exercise in viability testing in order to deliver maximum value and impact for the site, whilst considering cost, programme and carbon resource. The proposed ‘light-touch’ retrofit approach concentrated on new fabric to the front facade and lobby to dramatically improve the entrance sequence. Research was conducted to provide a sensitive new addition along Old Street, enhancing and preserving the eclectic character of the conservation area, following the traditional proportional principles of an ordered base, middle and top The building becomes lighter and steps back towards the upper levels in response to neighbouring buildings, in-keeping with the scale of the existing building.