Sarah Rüegg

Two wood stories

The forest envelops the city of Zurich and serves as a vital leisure infrastructure for its inhabitants. The green expanse is a haven for flora and acts as a crucial carbon sink, contributing to the city’s environmental resilience and to the health of its inhabitants. The forest, seamlessly woven into the city fabric, simultaneously acts as a productive space.

I want to take you on a journey starting in the Altberg-Lägern forest area 7. Nestled wit- hin the agglomeration of Zurich, 40% of the wood harvested here is processed in saw- mills. The other 60% of the wood is used as energywood or used as industrial material to make paper for example.

One of the mills processing entire logs is the sawmill P. Aecherli located in Regensdorf. It has been in family hands for three generations and is one of four sawmills remaining in the region of Zurich. To be able to pay salaries and cover production costs, the sawmill mostly processes high quality and precious woods. One of those precious woods is the larch tree wood. It is a very rare species in the region but has a high demand, due to its considerable water resistance. This makes it one of the few regional species that can be exposed to the weather and thus an alternative to imported timber. The larch tree is cut in the Ghei area, which is at the foot of the Lägern, where the underlying limestone is not yet as close to the surface as in other parts of the area. The tree is cut in winter when it is in a kind of hibernation and not filled with water. The felled tree is “cleaned” from branches, cut into five-meter pieces and piled up with other trees felled in the same area. In the local sawmill, the larch wood is cut into wooden boards, airdried and then gets processed further by various different clients. This trajectory follows the processing of the wood in a carpentry based in Winterthur. With simple means but a lot of expert knowledge on the behavior of wood, they produce benches for a company which designs public elements for the city of Zurich. Burri Public Elements has installed over five thousand benches all over the city by now. These benches are not only made of larch wood but of a variety of wood types. Because it is difficult to get local or even regional larch wood, due to the population of larch trees being very limited in the area, Burri Public Elements had to build up a network of local carpentries being able to deliver this material. The carpentries and saw- mills in the network are constantly trading raw and processed wood to be able to meet the consistent demand for certain woods. They depend on local personal contacts and on well-educated craftsmen to be able to meet high standards.

A stark contrast to the local journey descri- bed above can be found in the processing chain of spruce and fir wood. These two ty-pes of trees make up the biggest part of the Altberg Lägern forest area 7. They sometimes follow the same path as the larch, through a local sawmill to a small non-processed timber construction in the region. But often these two species take a far more industrialized timber processing path. They are ideally suited for the use as construction material because of the light weight and strong load-bearing ca-pacities. They can be processed easily in the sawmills without stressing the machines excessively and with glue lamination the dimen- sions of wooden buildings can be extended far beyond the natural limitation of a tree length.

When Karl Fredrich Otto Hetzer patented his system for glue-laminated timber in 1910 and built the world exposition hall in Brussels with this new system, it was the beginning of the engineered timber construction, which soon grew stronger. High quantities of spruce and fir cut in the forest and stored on piles are brought into big sawmills like Blumer Lehmann in Gossau. Every day trucks filled with spruce and fir from different forestries, at minimum 80 percent from Switzerland, arrive to be cut. After the cutting they are dried in adry chamber, using the heat gained through the burning of the waste from the sawing process. Parts of the spruce cut are then transported to a glue lamination production. All the lamellas produced have similar dimensions varying from 12 up to 26 centimeters in width and between 3.6 up to 4.5 centimeters in height. In length they are all five meters long. In difference to larch timber processing, here the quality doesn’t have to be perfect. Through the glue lamination process, weak points can be compensated for. Under high pressure the finger-jointed timber beams are glued together with polyurethane glue. For a yearly production of 21’000 cubic meters of glue-laminated timber beams, 80 tons of glue are necessary.

The processed timber beams are brought back to big carpentries like Blumer Lehmann, who have the digital tools and the space to produce timber elements for high rise timber projects such as the Tamedia building in Zurich which they built in 2013. At the time of construction this timber project was a show-case project for timber construction. Nowadays, with the changing awareness of the sustainability of building materials, timber is starting to gain importance in the construction sector. This becomes apparent in the changing norms and regulations as well. In the new cantonal sprucee laws made in 2015, there are no more height limitations for timber buildings. Thanks to this, different high-rise wood projects are now being realized in Switzerland, for example Pi in Zug, Ro- cket in Winterthur or H1 in Regensdorf. The latter one will be built only eight-hundred meters away from the P. Aecherli sawmill. Most of the construction built with glue-laminated timber uses spruce and fir wood. And despite the existing glue-laminated timber produc- tion possibilities in Switzerland, most of it is imported to save on costs for raw material and salaries.

In the building sector, wood is seen as the sustainable building material of the future. Its local occurrence and the CO2 capture of the forest and the timber are advertised fervently. Due to the high demand and the need for sustainable living space, timber production is changing into an industrialized process. It is an irreversible process of necessity. At the same time, local producers like the P. Aecherli sawmill are under a lot of pressure because of cheaper industrialized timber materials often also coming from abroad. With the standardization of timber production, expertise on processing and craft are lost. Therefore the local network shall be strengthened,and the expert knowledge could be preserved and passed on to the public. At the same time wood should be made more visible in the city on a small scale and learning from the moreindustrialized processes, the use of the material shall be done with more care for the entirity of the wood and not noly the prime pieces.

Public Wood Workshop

In the research of the trajectory around local wood and timber in and around Zürich the change of timber production into a more industrialized process became visible. With the standardization of timber production, expertise on processing and craft are lost.

This project intends to establish a workshop where the craft and knowledge of woodworking can be passed on from craftsman to the public. It should also bridge the gap between industry expertise and public understanding whereby new material interventions in the wood industry can be presented. It is positioned strategically within the creative hub, adjacent to the dynamo with its public metal workshop. Beyond being a mere workshop and educational facility for lay persons the building also connects to a larger network. It evolves into a meeting ground for woodcraft experts, completed with an adjoining exhibition space showcasing inno- vative wood-based building materials.

The new building uses the existing foundation of the Schutz und Rettung Provisorium that is located on the Limmat as its location and foundation. This building was established during the restauration and renovation of the Walche building. In 2025, after 5 years the renovation work is finished and the Provisorium will be taken away again. The wood element building on top of the steel structure will be taken back again by the carpentry imposing it in the first place, as they will rerent it. The foundation is planned to be demolished.

This project proposes to keep the foundation due to its highly labour and cost intense construction and deconstruction. On top of this foundation the new wooden structure follows a long tradition of productive spaces on the Limmat like a cotton mill or a florette spinning mill, that were demolished in 1950 due to the initiative of „freie Limmat“. The wooden building follows the structure of the preexistant foundation. This tradition of craftsmanship in wood is represented on the facade were an overleaving knot is connected with wooden dowels. This open structure not only offers new productive and creative space but also public space that opens up to the Limmat.

Catalogue for Public Elements

With the industrial production in timber construction, wood is becoming increasingly popular. The construction of high-rise buildings made of wood has begun in and around Zurich following the change in fire safety standards in 2015. At the same time, small sawmills are under pressure due to cheaper industrialized wood materials. Particularly glued laminated timber, which offers various construction methods, is setting new standards. Small sawmills often do not benefit from the flourishing timber boom in the city of Zurich. This project attempts to streng- then the local network of sawmills with a small-scale use of materials. The catalogue with public wood elements for the city of Zurich is a reaction to the existing public element catalogue. Working with wood for public elements not only offers the city the opportunity to use the cities own wood, but also creates a visibility of wood in the city on a smaller scale. In the long term, wooden elements could replace the current element catalogue. Moreover, the wood required for the production of these elements has lengths that even smaller sawmills can produce. The small thickness of the boards also means that large wood scraps can be avoided.

The catalogue works with a simple system that can be expanded. The combination of pliers and threaded screws makes it possible to use different qualities of wood, as it is an assembly-to-disassembly system. The catalogue is closely related to the planned public wood workshop of the city of Zurich. The production of public furniture can be seen as basic production in the public workshop, where the public learns how to use the machines under the gui- dance of an expert as an introduction to the workshop. This open-source catalogue provides the public with a system that can be expanded for other objects in public spaces. The aim is to encourage the public to further develop and rethink designs. By helping to shape public space, the public should also create a new awareness of local and resource-conserving construction. The catalogue is intended to encourage people to ‘do it themselves’ and is thus in the tradition of architects such as Enzo Marior 6a architects, who have created catalogues for private furniture construction.