In January 2013 one of our clients gave us the challenge of designing a 5 storey building in Chelmsford to meet disproportionate collapse design requirements. We took this challenge and developed a design that came as close to traditional construction as possible. We proposed using hollow core floor units with no vertical and horizontal tying, thereby avoiding the requirement for other expensive and time consuming forms of construction traditionally adopted by other engineers – such as RC frames, composite precast/in-situ floors or traditional construction with vertical and horizontal tying in the form of steel posts and continuous reinforcement bars. A substantiation of our design method was presented to the NHBC prior to production of tender issue drawings, was reviewed by principle NHBC engineers, and was then accepted. We were informed that no such proposal had been received by the NHBC before. Therefore we would consider ourselves pioneers in this technique. We have now carried out two projects using the same design method.