Hygrothermal performance of multilayer straw walls in different climates

Straw is becoming a promising alternative insulation material to improve the building energy performance
because of its low cost, large availability as cereal waste, its good hygrothermal properties, and its low embodied
energy. The goal of this paper is to assess the hygrothermal performance of multi-layered straw walls with
different boundary conditions. The study consists of evaluating five different straw-based wall assemblies, under
a continental (Arkhangelsk, Russia), a tropical climate (Brasilia, Brazil), a temperate Mediterranean climate
(Nice, France), and a cold desert climate Xinjiang (China). Numerical models of the heat and moisture transfer
through the walls using WUFI software are developed, calibrated, and validated through experimental results
from the literature. The chosen evaluation criteria are the total water content, the drying rate, the condensation
risk, the mold growth, the moisture quantity, the time lag, and the decrement factor. Results show that straw
walls with cement and/or wood covering can be used in tropical and temperate climates, coated straw walls with
additional air layers in dry climates, while insulated straw walls are best fitted in continental climates. In the
latter, the dryness rate varies between 7 and 40% with a low condensation risk of value in the range of 0–12%. It
can be concluded that the straw wall’s performance strongly depends on the interior and exterior added thermal
insulation layers since they affect the ability of the material to dry out.