Straw Houses: Going towards passive houses

Student thesis: Master thesis (including HD thesis)

  • Peter Vester
  • Sidsel Petersen Warming
This project fokuses on straw houses and development of these. Throughout the project there has been a collaboration with the association Friland that has experience with construction of straw houses. Straw houses in Friland are build with nature materials and are thereby very enviromentally friendly. In the building industri today passive houses and other types of low energy building are becoming more and more interesting. The focus is on the energy consumption from finished construction to the destruction meaning the service life of the building. However there is less focus on the energy consumption used to construct the building materials as well as energy used to recycle or destruct used building materials. This energy is one of the main focuses in Friland which is why they use materials like straw, clay or recycled materials such as old windows and doors. They want to reduce the energy used to construct the materials. The materials straw and clay both have a low energy consumption doing production, because they are natural and can be used almost directly from the field or ground. The question is if these houses can be constructed as low energy buildings in their service life? The project aims to find out how and if it is possible to develope a straw house with nature materials that fulfils the demands for passive houses. It would then be possible to build a house that is both enviromental friendly and with low energy consumption. There is not a lot of experience and knowledge about the straw houses in Denmark. The energy consumption for a straw house is therefore uncertain and the houses are build based on the limited experience and a presumption about the U-value for straw. In this project experiments are therefore made to determine the thermal conductivity of straw with different densities as well as an element with both clay and straw. These experiments are conducted in a hot box constructed by Aalborg University. With the thermal conductivity it is possible to determine the insulation power for a wall constructed with straw as the insulation material and thereby figure out if it is realistic to use straw as insulation in a house that should fulfil the demands for passive houses. To determine the state of the houses build in Friland today with regards to the energy consumption a blowerdoor-test and thermal imaging have been carried out in a house in Friland. The house is small, but based on the latest experience and ideas in Friland. The insulation in the house is cut straw that has been blown into hollow rooms created by wooden frames. The insulating is cohesive the whole way around meaning that nothing interrupts the insulation between the walls, roof and floor. The point of the blowerdoor-test is to determine how airtight the house is, because this has a big influence on the energy consumption. The thermal imaging determines where there might be problems with thermal bridges or leakages in the construction. From the thermal images the linear thermal transmittance can be found and compared with the calculated linear thermal transmittance from models in the program COMSOL. Both the linear thermal transmittance and the thermal conductivity are used in calculations in the programs PHPP and Be06 to evaluate whether the demands for passive houses are fulfilled as well as the demands from the building regulation. To industrialize the construction of a straw house two suggestions to construction of straw elements will be given. If these straw elements can become a reality this will lower the price for a straw house as well as lower the construction time which is rather long today.
Publication date2009
Number of pages337
Publishing institutionAalborg Universitet
ID: 17735283