Milson Island Indoor Sports Stadium | Allen Jack+Cottier Architects

Allen Jack+Cottier adopted an imaginative approach to materials, structure and form when designing the Indoor Sports Stadium on Milson Island in the Hawkesbury River, NSW. The client’s brief called for a robust, multi-purpose sports hall to be used for indoor sports such as basketball, netball and volley ball, as well as theatre and dance performances and exhibitions. Our design direction grew from our integrated and exhaustive environmental modeling, materials research and structural analysis process to become a study of the wind and rain, the flow of water, the sounds of the birds and the rustle of the leaves. The unusual asymmetrical curve of the hall arose from practical considerations of wind load, bushfire protection and maintenance. The main curve directs wind efficiently over the roof, while the indented curves at the base scoop wind inside to naturally ventilate the hall. There are no visible ridges, eaves, gutters, downpipes or skylights on the exterior. The continuous wall/roof shape dispenses with gutters, reducing maintenance and removing a major bush-fire hazard. The natural thermal ventilation created the wing shape. Smooth airflow required a clean, crisp interior skin. The design exploits the inherent properties of cross laminated plywood used to brace the steel portal frame, with the shape of the building designed to unload wind forces on this exposed site, thus reducing the weight of the structure by 30%. The steel frame, in conjunction with one cross laminated plywood bay, carries all the wind loads of 38m of building to the ground. Well almost to the ground! The structural engineer nearly had a heart attack when asked to include an uninterrupted slot between the floor and about the eye height of a twelve year old child. We love the idea that the kids can see the beauty of the landscape outside, whilst the taller adults are focused on the activities within. We wanted the building to slot ‘gently’ into the site. The building was positioned into a pocket between two lines of trees where we recreated the roll of the ridge which had been removed as part of an earlier quarrying operation on the site, helping to reduce the apparent scale of the building. At night, the curved wing shape of the new building acts as a proscenium arch to define the place for the campfire, an important part of each camp at the site. It works both for the audience inside looking out to the gathering space, and for the audience around the fireplace looking back into the hall. Attached amenities and storage modules service the fireplace, the bushwalking activities and the oval. They also serve to define a clear and strong entry space to the hall. A combination of twelve wind turbines and a series of floor mounted louvres ensure the building remains cool in Sydney's fierce summer heat. In winter, with the turbines and louvres closed, a heat plume forms to act like an insulation blanket. Rainwater falls clear of the roof into oversized rock gardens for natural filtering and collection for use in landscape irrigation and toilet flushing. Natural light from the roof windows, ground level slot windows and end walls create an almost art gallery-like feel to the hall. The gutterless design of the roof means there is no maintenance in terms of cleaning and a reduction in the likelihood of leaf build up during the fire season. The curved interior reduces the build-up of dust on the walls, which reduces additional “high cleaning” costs. Maintenance Manager, Milson Island – “You’d expect wear and tear on a building like this given its high usage but after a year and a bit it is still in mint condition. The building is almost kid proof.”