Moisture and Temperature Effects on Porous Building Insulations in NZEB Envelopes: A Review

This paper is a literature review study comparing the thermal, hygrothermal and environmental performance of synthetic porous insulation materials (EPS, XPS) with a bio-based alternative, sheep wool, in the context of NZEB requirements. Although petrochemical materials are widely used due to their low initial thermal conductivity, data reported in literature show that moisture accumulation produces significant increases of their thermal conductivity, leading to errors in the assessment of thermal loads. Sheep wool shows a comparable thermal conductivity, 0.032 and 0.054 W/(m·K), depending on bulk density, fibre quality and binder, and its hygroscopic behaviour allows uptakes of 35–40% water by dry mass at 100% RH with a moderate rise in conductivity, due to water is rather bound within the keratin than filling the pores. Its high vapour permeability limits the risk of interstitial condensation. Reaction to fire, sound absorption and limitations of wool usage, are addressed in dedicated section.