LIVING ON THE EDGE
Smart Design
The biggest engineering challenge with the pods was
dampening the structure to prevent unwanted vibration or vertical
movement, particularly when people are in the extreme end of
the overhang. "The natural frequency of the nine-metre pod is
eight Hertz," says Weber. "At that level, you need to start thinking
about the effect of vibration and how people will perceive that
level of vibration. It is a case of trying to dampen the structure as
much as possible."
The key to solving the vibration problem or vertical acceleration is the steel truss frame which forms the core of each pod. The trusses are made up of fully welded 150 UC 37 members. These are of sufficient weight and strength to minimise the vibration levels the structure generates. For lateral loads, the two main trusses are braced with diagonal 16-millimetre rods beneath the ceiling and under the main floor. However, the ceiling cables are likely to be replaced with a plywood diaphragm.
The floor itself is a sandwich of three components – the main structural components are cold-rolled-steel joists, the underside material is fibre cement board, and the top surface is particle board, which is ready to accept the finished surface. Insulation is sandwiched between the top and bottom layers.
The walls are largely doubled-glazed glass with extensive use of bi-folding doors. To prevent falls, the cantilevered end uses waist-high safety diamante glass panels. The exterior cladding can be varied from all glass to a more solid look with wall panels. Internal rooms are created using non-structural internal walls made from steel or timber framing with plaster board, which can be located anywhere within each pod for maximum layout versatility.
The roof is known as "warm roof", which is a flat roof design common in Europe. The roof comprises timber rafters then a plywood diaphragm and vapour barrier, which sits below tapered rigid insulation sheets called Enertherm. Waterproofing is achieved using two layers of bituminous membrane. Weber says the roof has a very high insulation rating to compensate for the amount of glazing used in the pods.
Each pod is transported to the building site with the steel frame, floor and roof already installed. Installing each pod in situ takes between five and six hours, after which services are connected to the building. Due to the torsional rigidity of the pods they can be transported to site with the glass already installed. The other key to any successful cantilevered structure is the foundations, which depend on the material on the site. On a rock site, rock anchors are drilled horizontally between seven and 10 metres into the hillside to secure the back of each truss. On clay soils, 450-millimetre tension piles are secured to a depth of four to five metres. On a flatter site, which falls away to a steeper bank, a concrete foundation can be used as a counterweight. On most sites a retaining wall provides additional counterweight for the suspended pod.
The first Smartpod home has already been completed in Queenstown, and Weber is confident that with New Zealand's hilly terrain there will be plenty of Smartpod homes appearing on hillsides in the coming years.
