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The use of vacuum insulation panels (VIPs) is under investigation by the National Research Council for use as a complementary material for current insulation systems. VIP composites, consisting of VIPs sandwiched between polyiso panels, were constructed and incorporated into a modified bitumen roofing system in Ottawa, Canada. The VIP composite, as well as a conventional polyiso system, were monitored in-situ for a period of five years to observe their performance. It was found that the composite VIP insulation outperformed the conventional polyiso system for all months and years monitored, providing an increased barrier to heat flow, reduced temperature driving forces for energy loss, and R-values that were on average twice that of the conventional polyiso system. The long-term performance was also assessed for the five year period and it was found that the VIP composite performed within a 10% margin of its original value for consecutive years. This study successfully demonstrated the energy saving potential that can be achieved through incorporating VIPs into current roofing and building applications.

An industry consortium study, Energy Resistance of Commercial Roofs (ERCR), has been developed by NRC to develop scientifically supported performance data on energy resistance of roofing systems that are constructed according to field practices. The ERCR consortium project had two major tasks. In Task 1, the objective was to evaluate the effective thermal resistance of current roof designs and validate their compliance with the energy code requirements and, in Task 2, the aim was to quantify the two thermal impact factors – thermal bridging from fasteners and thermal bypass from gaps between the insulation boards. This paper focuses on the Task 2-thermal bridging from fasteners. More than 100 experiments were conducted to quantify the impact of fastener density, fastener location, fastener diameter, and fastener penetration depth on the thermal performance of the roofing assembly. From the experimental data, the thermal bridging of fasteners was quantified in terms of the “Relative” decrease in effective R-value and Chi-factors (χ). The impact of fastener density revealed that the thermal bridging increases with the fastener density and also with the thermal resistance of the insulation with an average loss in effective R-value ranging from 5% to 14% for the tested configurations. The increase in the fastener diameter or the fastener area (#12 < #14 < #15) increases the overall heat flow through the assembly. In a multilayer insulation layout, fasteners installed in the bottom layer are shielded by the top insulation and can reduce thermal bridging from 30% to 70% relative to the through fastener from the top layer. From the experimental data, chi factors were developed to support calculation of point thermal bridging effects on the thermal performance of the commercial roofs, and also to fill in the missing gaps in the energy codes towards the thermal design of roofs.

The moisture design of exterior walls in a building envelope is an important task that needs to be carried out systematically to generate a sustainable and healthy built environment. Many conventional methods or practice guidelines are available for this purpose, based primarily on local traditions and with limited performance assessment records. In recent years, with the rapid development of global free trade and economy, new wall systems and unconventional materials have been introduced in every part of the world for reasons such as aesthetic appeal, cost effectiveness and so on. However, neither the long-term moisture management performance of these new wall systems nor the uses of unconventional materials have been assessed in a systematic way. The primary reason for this lack of assessment is the absence of a design-oriented methodology to perform the task. This paper presents selected results from a recently completed research project that demonstrate that it is indeed possible to assess the moisture management performance of exterior walls in a systematic way, using a hygrothermal modeling tool together with key inputs from a limited number of laboratory and field investigations. In this project the hygrothermal responses of exterior walls and their components were assessed with a novel moisture response indicator, called the RHT index, which is derived from relative humidity and temperature data over a time period. The results and discussion presented in this paper clearly show the need and usefulness of the application of hygrothermal simulation tool for the optimum moisture design of exterior wall systems in various geographic locations, when sufficient information is available from laboratory and field experiments.

This paper investigates the role of the vapor barrier in exterior wood-frame stucco walls with the help of a two-dimensional hygrothermal simulation tool, hygIRC-2D. For this purpose, the wall is subjected to the exterior weather conditions of six different North American geographic locations and three different interior climatic conditions. Seven different vapor diffusion strategies, generated by varying the water vapor permeance of the vapor barrier, installed outboard of the interior finish, have been studied to generate critical understanding on the role of vapor barrier in the wood-frame stucco walls. The outputs from the simulations have been analyzed with the help of a novel moisture response indicator called RHT index. Simulation results indicate that the vapor transmission characteristics of the vapor barrier, in terms of water vapor permeance, play a very important role in the overall moisture response of the wood-frame stucco wall. A very high or low vapor permeance of the vapor barrier does not produce the optimum moisture management strategy for the wood-frame stucco wall. Moreover, simulation results indicate that the removal of vapor barrier from the wall system can result in a heightened moisture response and a considerable accumulation of moisture in the interior gypsum board that may lead to severe consequences in particular, the premature deterioration of the interior facing gypsum board. It has also been observed from the simulation outputs that the optimum vapor diffusion strategy, that of limiting the vapor permeance of the vapor barrier, is not a function of interior climatic conditions considered in this study. It is hoped that the results reported in this paper will shed some light on a number of concerns raised in recent years on the role of vapor barrier in wood-frame stucco wall construction.

In Canada and other parts of North America, traditional wood frame exterior building envelope construction is widely used and its ability to manage the exterior and interior moisture and thermal (i.e. hygrothermal) loads is well known from the field performance observations over the years. However, this type of building envelope construction is not traditionally used in China and Taiwan. At present, the Council of Forest Industries (COFI), an association of British Columbia forest industry partners, is promoting wood frame building envelope constructions and developing the market for the use of Canadian wood products in China and Taiwan. However, this is not possible without knowing the consequences and the ability of the wood frame building envelope assemblies to manage the hygrothermal loads in the climatic conditions of China and Taiwan. This is a long-term performance issue that becomes even harder to resolve when there is no comprehensive field performance data, as in this case. This paper presents result from a research project that investigated the hygrothermal (i.e. thermal and moisture) performance of the Canadian wood frame exterior building envelope construction practices in the city of Shanghai (China) and Taichung (Taiwan). This has been done using a two-dimensional hygrothermal simulation tool. Three exterior wall constructions and two roof constructions were exposed to the exterior climatic conditions of Shanghai and Taichung. The first set of simulations was conducted with a wall construction that has no air leakage. Thereafter, two wall constructions were also simulated with various levels of air leakage through the wall assembly. The outputs from the simulations have been analyzed with the help of a moisture response indicator called RHT index. Simulation results indicate the relative performances and suitability of the different wall and roof assemblies in Shanghai and Taichung. It is hoped that the results presented in this paper will help to develop moisture and thermal (i.e. hygrothermal) design guidelines for the Canadian style wood frame building envelope construction in China and Taiwan.

Using numerical modelling to simulate and predict the hygrothermal (i.e., combined thermal and moisture)performance of building envelopes is very recent. Key questions include: how to model accurately coupled heat-air and capillary moisture transports in building envelope components; a satisfactory definition of a set of representative environmental boundary conditions to be used for long-term hygrothermal calculations; how to characterize the moisture- and temperature-dependent properties; the effect of aging and cyclic environmental conditions on porous building materials; and how to develop sound criteria to predict the moisture durability of building envelope components. This paper presents the findings of a research project involving detailed hygrothermal modelling. The heat, air and moisture results demonstrated that the in-house model could be adapted successfully for high-rise building calculations. The findings also show how the long-term hygrothermal performance of typical wall systems can be assessed using numerical modelling. A short description of an advanced in-house heat, air and moisture model, hygIRC, is also presented., 12th International Heat Transfer Conference: 18 August 2002, Grenoble, France

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.

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 (NRC-IRC) have compiled a database of measured air permeability and water vapour 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 (RH) 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

Water vapor transmission properties of building materials play an important role in the overall moisture management and durability of the exterior building envelopes. The cup method, as described in the ASTM Standard Test Methods for Water Vapor Transmission of Materials (E 96), is widely used in North America and other parts of the world for this purpose. Recently the latest ASTM standard (E 96/E 96M–05) has started taking into account various corrections (e.g., buoyancy correction, correction for resistance due to still air and specimen surface, edge mask correction, etc.) while analyzing the results obtained from the cup methods. This paper presents the results obtained from the laboratory tests carried out on more than 50 building materials. These results have been used to demonstrate the significance of various corrections on the measured water vapor permeability or permeance of various commonly used building materials or components. The results presented in this paper were discussed in the ASTM technical task group to underline the importance of various corrections for the calculation of water vapor transmission properties of various building materials.