In this paper, a double-skin steel building-demonstrator, set up using panels of five bio-based insulators and a classical mineral insulating material, is studied. The panels used in the demonstrator are made from industrially manufactured and commercialized bio-materials. To assess the suitability of these panels for use in cold formed steel envelope buildings, their advantages and/or the drawbacks (if any) of the synchronized records of temperatures, relative humidity and thermal flux of each panel are obtained using a system of continuous measurements. Data from 6 months of records in the roof of the demonstrator are used to assess the infield properties of the panels and the seasonal evolution of these properties in relation to the presence of the vapor barrier. The thermal resistance of each panel is determined from these data using two methods: the ISO 9869-1:2014 based on the Heat Flow Meter (HFM) method and an inverse problem identification method. All bio-sourced panels manifest higher thermal resistance than the classical insulation system, whatever conditions of use with or without barrier vapor. The seasonal variations of thermal properties are attenuated when a vapor barrier is used. No risk for water condensation inside the bio-insulations is revealed so far.

The use of innovative insulating materials can contribute to an energy-efficient design by improving the thermal performance of building envelopes while also reducing the embodied energy of materials. Ultra-low carbon steel envelope solutions with bio-based insulations are aligned with this approach. However, fire safety aspects in general and smoldering issues in particular need to be considered when using bio-based insulations. Accordingly, this paper proposes a system-level assessment of the fire performance of steel envelopes with bio-based insulations, not only identifying potential smoldering issues of the core material but also defining and evaluating strategies that could address these concerns within the system design. For this purpose, the variables that could affect the fire performance of wood fiber insulation sandwich panels were identified while considering the different stages of the smoldering phenomena, such as the influence of the joint design or mounting provisions for the initiation, the existence of air cavities, oxygen entrances or physically continuous materials with a tendency to smolder for the continuation, or the inclusion of limiting elements or mitigation layers for spread limitation. Finally, strategies for fire-safe enclosures using bio-based insulations are proposed, assuming smoldering affections in wood-derived materials and analyzing possible mitigation elements at the system level.