Maximilian Schade / Walter Fritz
Nearly unnoticed, a simple but rather smart construction system has evolved in Europe in the last 30 years, the strawbale buildings. Structural elements from wood are easily filled with strawbales and directy plastered with clay from both sides. The elements provide the perfect physical conditions for a healthy and comfortable indoor climate. This type of construction is diffusive, moisture regulative, well insulated, long lasting and free of any harmful substances. Countless projects in timberframe and strawbale filling have been realized in Europe, like the 5-storey FASBA-Complex in Verden, Germany. The Strohboid construction system is adapting these special abilities for freeforms and large elements. Timber gridshells can not only span large distances, but can also be used very well for load bearing or suspended facades. Any kind of straight or organic forms can be prefabricated with little additional work. We, Maximilian Schade and Fritz Walter, are probably among the first generation to be directly affected by climate change. Therefor it was important for us, to demonstrate within our Master Thesis effective solutions for carbon neutral constructions, and develop a signpost for ecological housing, which will inspire as many people as possible. At the Institute for Structural Design at TU Graz, under the supervision of Prof. Stefan Peters and Asoc. Prof. Andreas Trummer, we combined lightwheight construction methods with ecological materials. A light timber gridshell, covered with clay plastered strawbales and finished with wooden tiles, that’s the Strohboid construction system, possibly the most ecologic construction system today! 40% of all carbon emissions worldwide are emitted by buildings. Half of the CO² emissions in the lifecycle of new buildings are emitted by the production energy of building materials. In Europe, 10% of all carbon emissions are emitted by the production of buildings. With the use of organic, grown materials like timber or straw, approximately the same amount of carbon can be deposited within the construction, as is emitted by conventional materials. With this reversal effect, the housing industry could make a valuable contribution to climate protection. By using lightweight construction principles, starting with the building geometry in the form of a saddle surface up to the pre-stressed sandwich construction of timber gridshells and straw, the construction saves half of the building material compared to a conventional timber frame construction. In contrast to a conventional building, the Strohboid consumes 90% less production energy and thereby saves 17t CO² during the construction phase. The Strohboid is made of 10 tons wood and straw, which store an additional 20 tons of carbon. In addition, the building is free of artificial and pollutant substances and can be recycled, burned or composted at the end of its lifespan. Since the invention of the first strawbaler 150 years ago, strawbales are used to build simple houses. Today it is becoming increasingly popular due to the high level of residential comfort. Straw bales are easy to shape and are perfect for curved constructions. The straw bales are directly plastered with clay, which means they are protected against fire and pests and serve as a thermal insulation and moisture regulator. The Strohboid consists of two timber grid shells, the interspaces of which are filled with strawbales. The outer shell is prestressed against the inner shell, creating a stable composite construction. In order to realize the small radius of curvature with the required wood cross-sections, the timber gridshell is designed in bentwood technology. For this purpose, wood is heated by water vapor, making it soft and flexible. If it cools, it remains stable and resilient. We were able to carry out loadbearing tests on a prototype. The gained experience was used to calculate precise static models and to realize a prototype.
The master thesis Strohboid - Entwicklung und Test einer Stroh-Holz-Verbundkonstruktion was supervised by Andreas Trummer (Institute of Structural Design).