London Basement delivered a 200 m² residential basement beneath an existing property, extending to the front, under a shell and core contract. Works included excavation and basement formation, structural steel installation throughout, extensive temporary works, structural waterproofing, below-slab drainage and construction of the ground floor structure. An opening was created in the rear façade to accommodate a new single-storey extension, requiring coordinated structural alterations. Key challenges included concrete breakout from existing foundations, dewatering at ground floor level and maintaining support to the first floor while steelwork was installed. The project was delivered as a fully waterproofed box, on time and within budget, meeting both the private client’s and architect’s technical and programme requirements for a complex basement under an existing structure.