Wood in architecture
AHEC has donated American tulipwood to two spaces of the new Kālida Sant Pau building in Barcelona: the outdoor pergola and the trellised façade. The building is designed by architect Benedetta Tagliabue from Miralles Tagliabue EMBT studio, with interior design created by architect and interior designer Patricia Urquiola. The features of thermally modified tulipwood provide resistance to weather conditions and add warmth and elegance to the building.
The pergola design, under which visitors pass to reach the main entrance to the building, has been designed to act as a protective layer covering the garden. The tulipwood boards form small triangles and are framed by a steel structure, offering textural contrasts to the outdoor area. This design not only works to shield the outdoor space from surrounding buildings, it also offers an escape from the traditional hospital environment. The trellised façade consists of horizontal thermally modified tulipwood slats that allow light to filter through and offer views of the Hospital de Sant Pau complex, whilst still preserving the patients’ privacy. According to Benedetta Tagliabue, “The use of thermo-treated tulipwood was an excellent choice for the outdoor elements of the Kālida Sant Pau building because it has allowed us to add elegant wood elements and we have been able to use it in an optimum way for exterior applications”. David Venables, European Director of AHEC, says, “We believe that this technology is key for using wood in exterior applications. The market is growing, and designers and architects want to use wood, but for this to happen it has to perform well, look good and last or it simply will not be used. Thermo-treated wood does not use chemical products, it improves stability and has a minimal environmental impact compared to other techniques. We are delighted to have collaborated on the Kālida Sant Pau building and with this fantastic social initiative”.
Thermo-treated or thermally modified wood performs better and has increased durability, allowing it to be used in exterior applications with no need for additional protection. Following this thermal modification, U.S. ash, soft maple, tulipwood and red oak obtain Class 1 durability, the highest possible classification. The treatment process consists of gradually heating the wood to a temperature of 180–215°C for three to four days (the time depends on the thickness and species of wood). The treatment is applied in an oxygen-free atmosphere to make sure the wood does not catch fire and it can be applied using steam or in a vacuum. This process reduces the timber moisture content significantly to 4–6% (very low) and changes the physical structure of the wood, which limits its moisture absorption capacity. This provides the products with more dimensional stability and means they are less susceptible to twisting or losing their shape with changes of humidity. The thermal modification process also destroys the hemicelluloses and carbohydrates in the wood which are the main food sources for insects and molds. This makes the wood more resistant to rot without the need for surface treatments. The increase in dimensional stability and resistance to decomposition significantly extends the useful life of the wood and reduces maintenance needs. Also, the wood acquires an attractive dark color along its whole length. Lastly, despite the energy used in the thermal treatment process, the carbon footprint made by this process is compensated for by the fact that other protection treatments with significant environmental impacts are no longer necessary.