Text description provided by the architects. The aim was to make this tea house a model of energy efficiency and at the same time completely transparent to the surrounding natural environment. The pavilion lies at the end of a range of hills formed in the last ice age, when the earth was pushed more than 100 metres above see level (quite an achievement by Dutch standards). From the entrance the floor rises in a continuous spiral that wraps itself around a group of trees and cantilevers over 14 metres. The construction, enabling this cantilever, is made out of steel for tension forces and out of unprocessed solid oak for pressure forces. At the most pivotal point a big moraine supports the construction.
The building emphasises the ‘value and power’ of natural resources and demonstrates continued dominance of nature over culture. At the same time, what is left of nature can’t be experienced anymore without cultural intervention. We can intervene by buying land for conservation, as the Dutch Nature Conservancy continues to do. A much more important challenge is to change human behaviour - by raising awareness of both the power and vulnerability of nature through different media, including the (at first impression) dichotomous media of building.
The sustainable aspects of the Posbank pavilion can be recognized in both the building’s material selection and its use of energy. With regard to the choice of materials we have tried to be environmentally friendly. Concrete, plaster based on natural stone granulates, sheeps wool for insulation, sustainably produced woods (no hard woods), columns of (European) oak tree trunks, steel trusses easily recyclable after demolition, a vegetation roof and an accacia parquet for the restaurant floor are the materials used. The insulation underground is partly provided by expanded clay pebbles (as found in hydroculture potted plants).
The building is also characterised by its efficient use of energy. Solar panels are provided on the roof to power the hot water system. A heat pump is used to heat the water for both the underfloor and air heating systems. Water at a temperature of 8 degrees Celsius is pumped up from a depth of 120 meters before being cooled to 6 degrees and returned back to the ground. With this temperature difference and the large amounts of water used, enough energy is generated to heat the building. Furthermore, there is no active cooling system necessary. The large sliding doors in the facade provide ventilation and cooling and the grass roof absorbs a significant amount of the heat generated in hot weather. The glass facades are finished with a heat reflectant coating to further reduce solar gain. Rainwater is accumulated on the roof and stored for use in the water closets. Some of this collected rainwater flows over the indoor rock formation near the entrance to make the external climatological conditions perceivable inside.