The 1973 building was constructed using the CLASP Mk 4b system. CLASP was a building construction technique introduced post-war and popular in the 1960s for short-term, cheap and easily constructed buildings such as schools,fire stations, libraries etc. CLASP buildings of wood and concrete panel construction encompass a vast number of hidden voids for services. CLASP Mk 4b was the incarnation used between 1969 and 1972, measurements were imperial using 4" as the basic unit. Panels were multiples of this – that is 12 inches or 1 foot, 3-foot, 6-foot and 9-foot. The planning grid was 12x12 inches, and a structural grid of 36x36 inches. The preferred floor to ceiling heights were 8 ft and 10 ft. The structure was steel frame with a 6 ft bay.Scapebuild CLASP ID guide It was hung with external 10 ft by 3 ft pre-fabricated concrete panels. The interior partitions were built using plastic-faced, plasterboard-backed steel Stelvelite panels. There was a hung exposed-T ceiling with 36x36 inch mineral tiles. The void above was used for service ducting, heating, electric power and lighting. The system was not heavy which was important due to the difficult sub-soil, and quick to erect which was important due to the tight time scale. It was designed to have a 60-year life. Hindsight shows that the extensive voids were a design fault, and many CLASP buildings have been destroyed by fire and have posed an asbestos risk.
