The main structure of the WISE building is a large glue-laminated (glulam) timber frame, apart from the lecture theatre which uses rammed earth. The external walls are of hemp and lime, which is cast round the frame to create an insulated, air tight and breathable construction.
The timber frame is FSC (Forest Stewardship Council) certified European whitewood glue-laminated (glulam) timbers, jointed with steel flitch plates. Glulam uses small sections of solid timber glued side by side and end to end, with staggered joints, to make large beams and columns that can carry high loads over long spans. The formaldehyde glues are not particularly eco friendly, but very small quantities are used. Due to the size and complexity of the frame we were unable to source it in Britain, and eventually settled on a Danish supplier.
The lime binder, Tradical HB, was developed to use with hemp. It’s based on high purity air lime blended with other materials (including 15% cement). This was mixed dry with the hemp fibre and water was added as the material was sprayed into formwork erected round the timber frame - similar to the process of casting concrete. The material was sprayed against temporary shuttering to completely enclose the timber frame and create walls 500mm thick. With this material - Hemcrete® - we could provide a high degree of insulation (a U-value of 0.14W/m2K) and air tightness whilst remaining breathable. A self-coloured lime render was used to finish the walls.
Most of the roof is insulated with 450mm of Cellulose (recycled paper), to achieve a U-value of 0.09W/m2K. For terraced areas, 250mm of cork was used as insulation under 150mm timber decking, giving a U-value of 0.14W/m2K. Cork was also used in key places in the foundations, to prevent cold bridging. As cork is water resistant it can be used in situations where many other natural insulation materials would be unsuitable.
The finish for some areas of roof, such as the Sheppard Theatre, is sheet stainless steel. Producing this metal is energy intensive, but the main feedstock is recycled steel, so no new ore is usually needed. Stainless steel is extremely durable, and as it is valuable it will always be recycled.