Impact of Density, relative Humidity, and fiber size on hygrothermal properties of barley straw for building envelopes

Abstract

Biosourced materials are increasingly considered to replace traditional insulators to reduce environmental impacts and benefit from better hygrothermal buffering characteristics. Barley straw is cheap and abundant and can be manufactured into insulation material. However, it is necessary to understand their hygrothermal properties as a function of manufacturing to design proper assemblies. The present work aims to determine experimentally and analyze sorption–desorption curves, thermal conductivity, water vapor permeability, and moisture buffer value (MBV) of barley straw as a function of density, fiber size, and relative humidity. Expressions were developed to correlate hygrothermal properties with the characteristics of the samples. Results revealed thermal conductivity values from 0.0468 W/mK (low-density short-fiber dry samples) to 0.0799 W/mK (low-density short-fiber 90 % RH samples) and MBV from 2.12 g/(m2 %RH) for high-density long-fiber samples to 2.95 g/(m2 %RH) for low-density short-fiber samples. The water vapor diffusion resistance factors ranged from 3.34 to 11.20 depending on the method used (wet versus dry) and the sample characteristics. These results indicate that straw offers a good potential as an insulator and indoor climate regulator in buildings.