The Garden House is a 179m2 domestic annex at the far end of the rear garden of a Victorian house in South West London. A modern family conundrum was the unexpected catalyst for the creation of the new annex – the immediate need of a newly married couple bringing two families together and requiring additional space to accommodate altogether eight children across two buildings. The design of The Garden House has been driven by three challenges including the clients’ ambitious requirement for increased space; the need to incorporate compulsory flood-proofing measures due to the site’s close proximity to the River Thames; as well as complying with planning restrictions to prevent the overlooking of neighbouring properties. The annex house comprises five bedrooms, three bathrooms, a study and a kitchen/living room. The garden was excavated to create a high-sided watertight concrete courtyard, which increased the floor plate of the property without affecting the single storey appearance at garden level. The living areas are at courtyard level and benefit from full height glazing; the bedrooms are arranged at first floor level in clean white volumes that gently ‘float’ above the glazing. A bridge at garden level bisects the white box and marks the entrance to the property. Windows are discreetly located on the side and rear elevations to comply with planning restrictions and frame views out. A combination of internal lightwells and rooflights ensure that the bedrooms are flooded with natural daylight. It is the sunken courtyard, characterised by white-pigmented concrete walls and floor that defines The Garden House and lends the house an exotic sensibility. Sliding doors open up the corner of the house offering a seamless transition to a tranquil enclosed landscape in which to escape London life.