Chopped Straw As an Insulation Material: the Influence of Different Blow-In Technologies and Flame Retardants on Hygrothermal Properties

The demand for renewable resources in building construction is increasing, and wheat straw is an excellent option due to its superior environmental performance compared to traditional insulation materials. However, the hygrothermal properties of chopped wheat straw insulation have remained largely unexplored. At the moment, blown-in straw is only blown in vertically, although horizontal blowing would be more efficient depending on the situation. This study investigates the effect of different blowing techniques on the thermal properties of chopped wheat straw insulation, focusing on the difference between vertical and horizontal blowing techniques. In-situ-measured thermal conductivities were compared with design values used in energy balances. In addition, the long-term hygrothermal behavior of chopped wheat straw insulation treated with flame retardants was investigated. The methodology included heat flow plate measurements, needle probe measurements and laboratory measurements using the hot plate method. The results show that there is no significant difference in thermal performance between the blowing techniques. The measured thermal conductivities were lower than expected, challenging the current general normative moisture surcharge on the thermal conductivity of natural fiber insulation. The addition of the flame retardant had no noticeable effect on the hygrothermal properties of the chopped straw. Chopped wheat straw can be regarded as a highly ecological insulation material with great potential for the future.