David van Reenen

Correlation Between Water Vapor and Air Permeability of Building Materials: Experimental Observations

Two fundamental properties of building materials that influence the hygrothermal performance of building envelope systems are water vapor permeability and air permeability. The driving forces for water vapor and air transmission through building materials are, respectively, partial water vapor pressure and total air pressure differentials. The theoretical similarity of the driving forces would suggest the possibility of a relationship between water vapor and air permeability. During past two decades, researchers at the National Research Council of Canada—Institute for Research in Construction have compiled a database of measured air permeability and water vapor permeability properties of building materials commonly used in North America. This material properties database was examined to identify the degree to which air permeability and water vapor permeability of the building materials might be functionally related. The database was segregated into categories for different material types. An approximately linear relationship could, within some categories, be observed between water vapor permeability and air permeability. There were however approximately as many categories within which no relationship between the parameters was apparent as there were categories within which functional relationships between the parameters were apparent. Within categories where functional relationships were apparent, the form of the relationships generally depended on the mean relative humidity at which water vapor permeability was measured. In most cases, a definitive functional form of the relationship between water vapor permeability and air permeability could not be established.

Long-Term Thermal Performance of Impermeably Faced Polyiso Foam Boards: Field and Laboratory Observations

AbstractResearchers at the National Research Council (NRC) Canada–Construction Portfolio in association with the Canadian Polyisocyanurate Council conducted collaborative research activities on the long-term thermal resistance (LTTR) of polyisocyanurate (polyiso) foam insulation with impermeable facers. Polyiso boards are commonly used in building envelope constructions (roofs and walls) in cold regions. The primary objective of the research project was to contribute towards the development of a comprehensive test procedure that could be used to measure the LTTR of polyiso foam insulation products with impermeable facers. As a part of that initiative, a project was initiated in 2001 that consisted of accelerated aging tests using thin slices in parallel with a field investigation in which polyiso boards were installed in a purpose-built test hut at the NRC’s Ottawa campus. The polyiso boards installed in the field were monitored for a period of 6 years and subsequently removed from the test hut and tested...

Preliminary Characterization of Physical Properties of Cross-Laminated-Timber (CLT) Panels for Hygrothermal Modelling

Cross-laminated-timber (CLT) panels are a type of relatively new wood-based structural panel, typically manufactured by laminating three or more layers of lumber together, with each layer rotated 90° relative to the neighbouring layers. This study explored preliminary assessment of the physical properties of a range of specimens for the purpose of initiating generating material property data for hygrothermal simulation of CLT building enclosure assemblies. Three types of five-layer CLT panels (nominally 130 mm thick) were made with Canadian softwood species, including spruce-pine-fir (SPF) from Eastern Canada and British Columbia, and hem fir from British Columbia, all glued with emulsion polymer isocyanate (EPI) as the adhesive applied between neighbouring layers. One type of three-layer CLT (nominally 90 mm thick) commercially manufactured in Europe using European spruce, with polyurethane adhesive, was also tested. Physical properties including density, thermal conductivity, liquid-water absorption, water-vapor permeability, sorption (moisture storage function), and air permeability were measured, mostly based on established international standards. To assess the impact of the adhesive on the hygrothermal properties of CLTs, test specimens used for most tests included at least one layer of adhesive, except those used for sorption tests, which used very small specimens. The properties were expected to mostly reflect the properties of the lumber used for CLT manufacturing. Variations in properties were found among these different CLT specimens; however, it was generally concluded that the differences caused by wood species and manufacturing methods would not be large enough to cause considerable differences in the hygrothermal properties or significantly impact the outcomes of hygrothermal simulation. With small-scale testing and very limited replication this study showed that the water-vapor permeability of CLT generally increased with an increase in relative humidity (RH), and the air permeance of the CLT specimens without visible gaps and checks was negligible.

High Performance Stucco to Optimize Moisture Management in Wood-Frame Stucco Walls

Stucco or portland cement plaster is widely used in North America as an exterior cladding material for the wood-frame walls. Recent computer-based numerical simulation studies at the National Research Council (NRC) Canada, Institute for Research in Construction (IRC) have indicated that low liquid diffusivity and high water vapor permeability of the stucco material can positively influence the overall moisture management capacity of wood-frame stucco walls. This paper presents the results from experimental and numerical modeling studies carried out at the NRC-IRC on the development of high performance stucco materials and its effect on the overall moisture management capability of wood-frame stucco walls. Liquid water and water vapor transmission properties of several commercial/conventional stucco materials and some newly formulated compositions were measured and compared under laboratory conditions. The experimental results suggest that by appropriate choice of the mix composition, addition of a proper hydrophobic admixture, and using aggregates with a hydrophobic coating, stucco material with lower liquid water diffusivity can be produced without reducing the water vapor permeability. The results from the numerical modeling study show newly developed high performance stucco materials can significantly improve the moisture management capability of wood-frame stucco walls.