The Moisture performance of Straw Bale Construction in a Temperate Maritime Climate

Jim Carfrae’s PhD thesis from University of Plymouth, UK, is now available online at

This thesis is an investigation into the moisture performance of straw bales used in the construction of buildings. In order to assess the moisture performance of the straw bales in the walls of a building in this damp climate, a simple and effective means of measuring the moisture in-situ has been developed as part of this research. The overarching methodology for this research is to develop a more accurate version of a probe that uses a block of wood to measure moisture. An environmental chamber in the laboratory has been used to establish the hygrothermal relationship between the timber to be used in the probe, and samples of the straw used in construction. This is the first time that a continuous set of sorption and desorption isotherms have been created for samples of straw and timber simultaneously, a process that took six months to complete. This data was used in the design of a new wood block probe, and examples of the new probes were installed in the walls of a straw bale house with a known moisture history. Fourteen diverse examples of straw bale construction were selected as case study buildings. Having been surveyed for this research, a number were then selected to have the new probes installed, and evidence of their moisture performance was recorded. Sufficient data was acquired through this process to confirm the suitability of straw bales for use in the construction of buildings, in a temperate maritime climate.

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