Hygrothermal performance of natural building materials: Simulations and field monitoring of a case study home made of wood fiber insulation and clay

This contribution presents temperature and relative humidity data monitored over nearly two years for a case study building made of natural building materials. The case study building is a single-family house located in Denmark made of wood fiber insulation, wood fiber boards and indoor clay plaster without any membranes. Three different types of cladding systems have been tested: 1) mineral plaster rendering; 2) wood cladding applied directly over wood fiberboards; 3) wood cladding with a ventilated cavity. Monitored data is provided and compared with simulations performed with a commercial hygrothermal software. The moisture content and mold growth index are calculated from monitored data. The data indicates that the hygrothermal performance of the roof is excellent (RH < 70%); the hygrothermal performance of the walls with the three different cladding systems is good; one out of two sensor groups in the floor exhibits a moisture content up to 18% at the cold side of the insulation during summer and fall. Securing sufficient and evenly distributed crawlspace ventilation is recommended for eliminating concerns of eventual mold growth. Measurements show that materials employed in this house respond quickly to moisture changes, more quickly that simulated data. This work highlights the need for validating and adjusting WUFI simulation results with measured data to provide reliable results for building envelopes composed of highly hygroscopic plant-based materials. For these assemblies in these conditions, including a vapor retarder is not needed for achieving a satisfactory hygrothermal behavior.