We are proud to announce that we have submitted our final report for the AIA Upjohn Research Grant: Thermal Performance of Facades.
Preview the report:
This investigation seeks to quantify the effects of thermal bridging in commercial facades and then propose alternative solutions to improve performance. Utilizing infrared images taken from targeted assemblies at 15 recently completed buildings; we have determined the actual performance and R-values of a range of façade types and conditions. We have compared these figures with the theoretical R-values calculated using materials specifications to quantify the discrepancy between theoretical design and actual performance. Although several insulation assemblies performed well without thermal bridging losses, complete assemblies were typically in the order of 50% less effective than the theoretical model. In certain complex assemblies, the research identified facades with as much as a 70% reduction in effective R-value.
Having understood the magnitude of the problem that is faced by typical construction detailing, the purpose of this investigation is to study methods for improving typical details to bring the theoretical and actual performance into closer alignment. Based on thousands of images collected, we identified 16 areas of thermal bridging that might commonly occur in commercial structures using industry standard details. Broken into two broad categories of façade systems and transitions/penetrations, they address systems such as curtain wall supports, rain screens, existing wall renovations and transitions such as parapets and foundation wall systems.
In order to test the benefits of proposed improvements, we developed 2-D heat transfer simulations of the observed conditions and calibrated these models to the data measured in the field. The thermal modeling provided insight into the most influential paths of heat transfer which helped to direct the efforts of pursuing detailing improvements.
Not surprisingly, assemblies with external insulation or uninterrupted insulation performed quite well. Systems with complex façade anchoring structures as are often used for brick veneer or rain screens, on the other hand faired more poorly. The research suggests that continuous penetrations such as traditional shelf angles and z-girts have a significant effect on thermal performance. The impacts of the assemblies can be substantially mitigated through discontinuous support that spans through the insulation. Improvements can be further reinforced by specifying low-conductivity materials avoiding aluminum and carbon steel.
Looking beyond the most typical façade details, the study also explores improvements to interfaces such as around windows and at roof and floor transitions. These assemblies tend to see comparatively high levels of thermal bridging and while they may not drive building heating and cooling loads, they can lead to performance concerns. In particular, the localized increased heat transfer associated with anomalous penetrations can lead to thermal comfort or condensation issues.
The study concludes that with relatively modest changes, typical façade detailing can be significantly improved to ensure that the structures we build perform as anticipated. Awareness of thermal bridging has been elevated over the past few years and this has led to the development of new materials and products marketed to address the problems. Our research suggests however, that there are no easy solutions and careful detailing must be coupled with the selection of non-conductive materials that penetrate through insulation barriers intermittently.
Don’t have time to read the full report? We’ll be posting about each individual section over the coming months. Get up to speed on Curtain Walls.