Designed on 'environmentally progressive' principles, the zoo building has relatively simple construction but sophisticated methods of natural ventilation. The roof is made up of 250mm x 50mm rafters trimmed with box-ply edge beams and resting on 750 x 450mm 'Toblerone-shaped' box-ply purlins, supported on timber columns at 6m centres. CorTen steel sinusoidal- profiled sheeting, insulated with Actis reflective insulation, forms the roof covering.
A row of five ventilators along the ridge draws air out of the building. Each is a cone-like three-sided shape with a cowl raised above it on stainless steel supports. The height and volume of the ventilators and the position and shape of the cowls above were calculated to maximise stack effect.
Inside each ventilator a pair of insulated flaps opens and closes on motorised hinges. Two are fitted with fans which operate in still air conditions.
Because all three sides of the five ventilators are identical, a mould system of manufacture was practical and cost effective. grp was chosen, a material with improved technology giving good colour retention and water resistance. Each ventilator was cast in three identical sections. The vertical edges are reinforced with ply strings, bolted together with a shadow-gap detail. At the base the strings extend and are bolt-fixed to the rafters. Blue/grey in colour, the external surface is profiled to emphasise the form and pick up shadows.
A Corten steel collar is tucked inside the base of each grp form; it accommodates variation of between 15 and 30 degrees in the roof pitch.