Evaluating the use of straw bales in achieving passive house certification (PHIUS+ 2015) in western Canada

Achieving Passive House certification requires super insulation which can significantly raise the embodied energy and carbon footprint of a project, effectively front-end loading the climate impact, especially where petrochemical foam-based products are used. This research sought to evaluate the use of straw bales - a low embodied energy, carbon sequestering agricultural by-product - to achieve PHIUS+2015 certification. A straw bale wall system was adapted to a single-family detached reference house designed to meet the Passive House standard. The wall system was evaluated for applicability across three Western Canadian cities using WUFI Passive energy simulation software to evaluate compliance; thermal bridging and hygrothermal performance were also evaluated. It was found that the proposed straw bale wall assembly satisfied the PHIUS+ 2015 requirements in all three locations - Saskatoon, Calgary, and Kelowna - with only minor changes required to the reference house design. The annual heating demand and peak heating load, the two targets most sensitive to design changes, were, respectively, 4% and 8.6% below the target in Saskatoon, 63.1% and 21.3% below in Calgary, and 63.1% and 32.6% below in Kelowna. The research also revealed that maintaining a high degree of air tightness is essential for satisfying the requirements. Overall, this research demonstrates that straw bales can be a beneficial component in creating high performance enclosures without exacting a large embodied carbon footprint.