Chilliwack Building Climate Driven R-value Research

Chilliwack Building

This case study is based on a larger study of conventional roof performance by RDH Building Engineering Ltd. and was also presented at the 2014 RCI Symposium on Building Envelope Technology, March 20-25, 2014.

A large-scale field monitoring study was implemented in the Lower Mainland of British Columbia with the intent of measuring the impacts and benefits of roof membrane color and insulation strategy on the long-term thermal and hydrothermal behavior and performance of conventional roofing assemblies. Three different 2-ply SBS roof membrane cap sheet colours were installed over three different insulation arrangements for a total of nine unique test roof assemblies which were installed on an industrial building located in Chilliwack within the Lower Mainland of British Columbia, Canada. Chilliwack is located in ASHRAE Climate Zone 5, and has a climate similar to the larger nearby metropolis of Vancouver, though as it is farther inland, it typically gets hotter in the summer and colder in the winter. The average annual temperature at the Chilliwack airport, located approximately 1 km (0.6 miles) from the site is 10.5°C (50.9°F), and the average July and January temperatures are 18.5°C (65.3°F) and 2.2°C (36.0°F) respectively (Environment Canada 2013).

Sensors were installed within each of the roof assemblies to measure material and surface temperatures relative humidity, moisture content, heat flux, and dimensional stability of the insulation.

Project Location

Chilliwack, British Columbia

Insulation Arrangement Apparent R-values

Laboratory measurements were made of the apparent R-value/inch for each insulation product and then the results were used to determine the apparent R-values of the three insulation arrangements for this study, which are shown below.

By measuring both new and aged samples of polyisocyanurate (polyiso) insulation, the long-term aging impacts on the thermal performance of the polyiso were also predicted. This plot demonstrates the sensitivity of the apparent R-value of the different roof assemblies when exposed to either extreme cold or hot outdoor temperatures.

While the roof assembly constructed with polyiso has a rated R-value of R-21.3, when exposed to cold (-10°C (14°F)) the performance of this roof assembly reduces to R-20 or potentially as low as R-16.5 depending on aging effects. When exposed to hot temperatures (60°C (140°F)) the apparent R-value is reduced to R-16.5 or potentially as low as R-14.0 depending aging effects. In the hybrid assembly, the use of a layer of stone wool insulation (in this case, equivalent to approximately 45% of the assembly R-value) over top of the polyiso significantly improves the effective R-value of the polyiso as it keeps it near optimum temperatures (which are similar to typical interior temperatures), and therefore results in a better assembly R-value in cold and hot conditions. The roof assembly insulated with entirely stone wool insulation has a more stable R-value (increasing at colder temperatures, but decreasing at hot temperatures from rated R-value), and is not susceptible to a loss of R-value with age.