Plateau Hut

Engineering Against the Elements

A safe and ideally snug hut needs to be built in the Southern Alps − one of New Zealand's most hostile environments. Site access is difficult, and construction must be completed before winter. The hut must withstand all imaginable weathers and stay standing for at least 70 years. Who better to take up the challenge than Derek Chinn, advanced alpine climber and structural engineer?

When asked to design a replacement hut for Aoraki Mt Cook, Derek Chinn MIPENZ knew it would be a challenging feat of engineering. Typically, he faced the project as he would a great adventure.

A year ago Mr Chinn climbed to the summit of Mt Everest (see e.nz magazine September/October 2004). He is not a professional climber, but one of the few Kiwis to have climbed the 8,848-metre mountain while holding down a day job.

When Prime Minister Helen Clark officially opened Plateau Hut on 12 May 2005 she acknowledged Mr Chinn as an Everest summiteer and as an accomplished designer and structural engineer, describing the new hut as a "great technical achievement". This jewel in the crown of New Zealand's alpine hut network is attracting international acclaim for its innovative design.

"Plateau Hut is the single most important alpine hut in New Zealand because it is such a popular base for ascents to the summit with climbers following in the footsteps of Sir Edmund Hillary," says Mr Chinn. He has climbed to the top of Aoraki Mt Cook nine times via various routes, and stayed in the old hut 20 times. So he had mixed feelings about replacing it: "It had real character, and any climber that stayed there would have a real connection to the building – especially after reading the hut book and seeing who made it to the top and who never came back."

This case study is reproduced with permission from e.nz magazine. Subscriptions to e.nz are discounted for schools and TENZ members.

Planning

For Mr Chinn the greatest achievement was constructing the building, incorporating a variety of innovative details, on the inhospitable and inaccessible site. The design had to address serviceability and strength issues, and allow the building to be transported to the mountain and assembled between February and April, when the site is free of drifting snow.

The hut weighs around 60 tonnes, all of which, along with construction accommodation, plant and staff, had to be transported to site by helicopter. The design was modular so that each structural component could be flown to the site and placed safely. The separate modules were then connected and clad to produce a weatherresistant, serviceable and robust structure.

Design

Innovative engineering puts the hut at the cutting edge of international alpine hut design. At 18m long and 7.2m wide the footprint of Plateau Hut is larger than the available rock projecting from the glacier, so the southern end of the structure cantilevers out about six metres toward the Hochstetter Icefall and the Tasman Glacier.

To support the cantilever section of the hut, and to span the gap between suitable foundations, the walls are designed as "bridge trusses". Each wall has a substantial steel beam below the floor and a second steel section embedded in its top. The two beams are clamped around the 150mm thick timber walls with three-metrelong steel rods. The whole structure is tied to the rock foundations with 66 metre-long high-strength steel bolts grouted into the rock with epoxy.

Smart elements

A significant factor in the deterioration of huts is the accumulation of internal moisture from cooking fumes, damp gear, and users' breath. There is also the potential for carbon monoxide poisoning. Mr Chinn's design ensures effective ventilation to remove carbon monoxide and moisture-laden air. It incorporates a sealed paint system and a vapour lining inside the ply wall linings to provide further protection.

Plateau Hut is limited to solar power, so the ventilation system is passive. It has to function in nearly all conditions, and prevent snow from entering the hut. The design incorporates "stilling boxes" beneath the floor to allow air to flow into the building, while slowing it sufficiently to make it drop airborne snow. Ducts along the ceiling and cowled extraction ducts at the gables allow humid air and carbon monoxide to escape. The system also has silenced baffles and can be shut off.

Mr Chinn also designed the floor to slope imperceptibly toward drains made of steel. These drains allow vigorous cleaning of ice build-up, a safety consideration as it prevents icing of the floor and water building up inside the hut.

To manage condensation on windows, which untreated would cause water to enter the reveals and wall framing, Mr Chinn designed drip trays for retrofitting to the proprietary frames. Drain holes cannot be used in the frames themselves as water would be blown back into the hut in windy weather, and would freeze inside the frame extrusions in cold weather.

The thermal break double-glazed windows have toughened glass. They also have to act as fire-escapes in an emergency. If the windows were accidentally left open or unlatched they could be blown off their hinges, allowing snow to fill the hut. Therefore ventilation sashes have been incorporated in the design, and signs request users not to use the fire escape windows for ventilation.

Doors are a challenge for hut designers; normal domestic or industrial doors simply do not work in alpine environments. Plateau Hut has a single door with a triple set of rubber seals, and a door jamb fabricated from a 10mm steel plate.

The unique toilet design is likely to set a precedent for all future alpine toilet designs. It is a total containment system, specially founded on gravel away from the hut. The waste is periodically pumped out and flown from the site for disposal. A critical requirement was the need to avoid the discharge of human waste to the glacier or any part of the mountain as this would be culturally offensive. The area around Aoraki Mount Cook, including the hut site, is of significant cultural value to the local iwi, Ngai Tahu.

Outcome