Four stories of additional floor space has been added to a building for the publisher Book Works in Shoreditch. The existing building is situated in a very old and over developed part of London with difficult and restrictive boundary conditions. The proposal partially infills an existing light well allowing the existing floor plates on all floors to extend to the site boundary. A fully glazed flank wall allows daylight to penetrate into new and existing working areas. This glazed wall itself forms the edge of a new light slot that brings sunlight to a small external terrace at first floor level. Horizontal glazing in the terrace allows light into the ground floor below.