Moisture Movement and Mould Management in Straw Bale Walls for a Cold Climate

straw bale;building science;mould;hygrothermal;field study;Civil Engineering

Bronsema, Nicholas Rangco

University of Waterloo

关键词: straw bale;    building science;    mould;    hygrothermal;    field study;    Civil Engineering;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/5536/1/Bronsema_Nicholas.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

There is a growing interest in straw bale construction for its low embodied energy andinsulation value. Early studies of its structural behaviour and fire resistance have shown it tobe a viable alternative to traditional building techniques. However, the biggest remainingobstacle to widespread acceptance is the moisture behaviour within the straw bale walls,especially as it concerns mould growth. The uncertainty of this behaviour leads to thehesitation of building officials and insurance providers to freely accept straw baleconstruction. Therefore, this study investigates the moisture, temperature and mould growthin straw bale walls, through a combination of analysis, dynamic modeling and field studies.A study of mould is presented along with the current methods available for predicting mouldgrowth.Moisture is the primary controllable factor to mould growth in buildings. Therefore, anunderstanding of moisture accumulation within straw bale walls is necessary to provide a safedesign that precludes mould growth. This study compiles the current state of knowledge ofthe hygrothermal properties of the materials used in straw bale walls. Then a parametricsteady-state analysis is conducted to show the expected behaviour of vapour diffusion and theeffects of the material properties.Two 14”thick x 6’ wide x 8’ high straw bale test walls were constructed: one was renderedwith a typical cement-lime plaster and the other with a clay plaster. Temperature andmoisture were monitored throughout the walls for over a year. These test walls provide moreinformation on the macro behaviour of the walls to both vapour diffusion and, moreimportantly, rain.Hygrothermal computer modeling was conducted and compared to the test data to assess itsaccuracy. Thermal modeling was successful, while moisture modeling was found to be moredifficult due to a lack of accurate rain data. With better climate data it is expected thataccurate hygrothermal modeling of straw bale walls is possible.The result of this work is a general starting point for more detailed studies of thehygrothermal behaviour of straw bale walls with the ultimate goal of assessing the mould riskfor various construction techniques and locations.