Laboratory for sustainable construction

Office buildings rarely cause a stir, but the HoNR is quite different: a simple frame construction makes it possible to customise the floor plan as desired by arrangement of the inner and outer walls. Transparent façades and a jointless outer shell also create a pleasant working environment. Furthermore, the HoNR is more than just an innovative office building; it will also serve as ETH Zurich’s research laboratory for sustainable construction using hardwood.

Six professors from the Institutes of Structural Engineering, Building Materials, and Technology in Architecture and their research groups were involved in the construction of the building, implementing findings directly from their research projects. The inauguration does not mean their work is complete – they now want to test the technologies over a longer period and find out where their strengths and weaknesses lie. ETH President Lino Guzzella says of this unique new building: «The House of Natural Resources is a good example of on-site interdisciplinarity. It shows how wood, an indigenous raw material, can be used in a sustainable and technically smart way.»

Adaptive solar modules

One testing ground is the façade of the building: on one side of the building, scientists have assembled an adaptive solar façade that generates electricity and helps regulate the building’s energy requirements for heating and cooling. The façade consists of mobile modules of thin film solar cells, which move by compressed air-controlled drives. With these actuators, the solar cells face towards the sun and also adapt to the heat and lighting requirements of the building, in particular the needs of the users.

In future, the scientists envisage a solar element system that will track the sun using a special bi-layer wood module that exploits wood’s tendency to swell and shrink upon changes in relative humidity. Two layers of wood are glued together with perpendicular fibre directions. Upon changes in relative humidity, the layers bend accordingly and create a moveable wood element. As relative humidity decreases during a sunny day and rises in the late afternoon and at night, the bi-layer wood elements can work as a natural drive for solar modules to track the sun.

The scientists have also developed new surface coatings for wood façades that provide enhanced UV protection and water repellency. Such façade elements will now be tested on the actual building for their outdoor durability.

World firsts for Swiss wood

The HoNR is not only unique in its innovations, but also in its construction: it uses the first wood-concrete composite slab made of beech wood from Swiss forests. A beech wood plate approximately four centimetres thick is used both as formwork and reinforcement, and also provides an aesthetically pleasing surface. The new composite slab has similar load-bearing properties as a reinforced concrete slab, the most commonly used load-bearing floor element in Switzerland. Another unique feature is the roof structure with a beech wood slab. The beech lamellas are arranged crosswise, which distributes the loads in two directions as in a concrete slab.

The frame structure of the HoNR is made of Swiss wood, with the columns made entirely of ash and the beams made of a combination of ash and spruce to increase their strength. Additionally, all the beams are post-tensioned with a cable running through the inside of the wood. As a result, they centre themselves, meaning that the entire frame structure is particularly flexible and significantly more earthquake-resistant.

Monitoring wood’s properties

ETH Zurich researchers have installed a comprehensive monitoring system in the HoNR to capture how the building behaves over the years: they will measure the moisture in the wood frame construction and measure deformations with the help of a tachymeter. Special sensors will measure the relative displacement between wood and concrete in the composite floor. The researchers set up a dense sensor network during construction to analyse how the frame structure behaves, and with 16 load cells they can also measure the tensile force in each tensioning cable.

The effectiveness of the new technology will be observed through daily use. «We will document user satisfaction with the building,» explains project leader Andrea Frangi, Professor of Timber Engineering at the Institute of Structural Engineering at ETH Zurich. He hopes that the findings of the project will also inspire the Swiss forest industry, as he sees great potential for Switzerland in timber construction. The proportion of deciduous trees in Swiss forests is increasing as a result of global warming. «Swiss wood has a lot of potential,» he says. «We hope that companies recognise this and continue to pursue our approach.»

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