Energy-Efficient Retrofit of Wooden Heritage Buildings in Chiang Mai by Nature-Based Interior Insulation on the Basis of Typha

The traditional wooden Thai house, which also can be found in Chiang Mai, represents local and sustainable climate adapted building tradition with an open construction designed for high natural air exchange rates to achieve a more convenient thermal comfort, maintain good air quality, and remove moisture. However, due to urbanization and climate change induced rising temperatures, tolerable indoor temperatures are no longer ensured to a sufficient extent by natural ventilation. Moreover, the unhealthy air pollution in Chiang Mai also affects the indoor air quality negatively. Thus, today many wooden houses are retrofitted with air conditioners, which lead to high energy consumption and contribute to the amplification of the urban heat island effect, or are even demolished. These circumstances have led to a sharp decline of traditional wooden houses in Chiang Mai and thus to the loss of cultural identity. Many houses have been replaced by concrete buildings, which also means a significant decline in terms of ecologic building design. Thus, it is important to preserve traditional wooden houses by retrofitting them with new sustainable, climatefriendly technologies and materials. This report presents possible solutions to address these challenges. Workshops were held at Chiang Mai University, where several solutions developed at Fraunhofer IBP were presented and discussed with local stakeholders. Especially the Typha board, an innovative construction and insulation material made of cattail (Typha), was considered as particularly interesting.
Typha as a raw material combines numerous structural, building-physical as well as ecological and economic advantages like low thermalconductivity, mechanical strength, and biological resistance. Moreover, the plant is widespread throughout the world, can be established very fast and is characterized by an enormous productivity. It also can be used for the creation of ecologically valuable wetlands with important functions like a long-term bondage of CO2, water retention, and purification of nutrient polluted surface water. In addition, the magnesite bonded Typha board is hardly flammable and completely compostable. Due to its insulating and stabilizing properties, it could be used as interior insulation and for reinforcement of load-bearing structures or stiffening of the buildings. Additionally, the Typha board could be used to seal the countless joints of the walls to substantially reduce the infiltration of polluted air. Furthermore, a reduced air exchange rate combined with thermal insulating properties of Typha increases the effectiveness of air conditioners and decreases the energy consumption of electricity significantly. The next step for the CHARMS-team will be to assess the transferability of the Typha board in wooden houses in Chiang Mai with the aim of retrofitting them in an energy-efficient and sustainable way. For this purpose, it is planned to conduct comparative simulations and modeling and thus to investigate its performance regarding climatic boundary conditions in Thailand. At the same time, the options to produce Typha in the urban hinterland are assessed considering questions of energy efficiency, water retention and purification, and food security from a nexus perspective.