A family had only just moved into this 1920s detached house in Herne Hill when they asked us to make it work harder: rooms were disconnected, one bathroom served every bedroom, and there was nowhere to work. We added a loft floor and retrofitted the whole house to low-energy standards, without extending into the garden. Kitchen, dining and living now share one space under a circular rooflight, and the garage became a study. Three elevations are insulated externally, every window is triple glazed, and an air source heat pump has replaced the gas boiler.