With today’s push for building the most sustainable and energy efficient building, it is increasingly important for design and construction teams to understand how different building enclosure components and materials function once installed as a complete assembly. Building enclosure under-performance may lead to unforeseen ownership costs and repairs, and failing to achieve anticipated energy savings. Such issues can have been avoided through proper considerations during project conception, design, and construction.
Depending on stated R-values and material, thermal resistance can be misleading and reduce potential energy savings if they are not considered as a full assembly. For instance, heat (or energy) is transferred from the conditioned interior space to the building exterior through conductive (metal) attachments, anchoring the exterior wall cladding to the structural steel wall framing. These highly conductive thermal bridges cause direct heat flow paths through the insulation. Depending on the attachment method and insulation depth, they can reduce the overall thermal resistance of a wall assembly by upwards of 50%. A wall with R-13 within metal studs and a continuous R-8 is reduced to R-16, and is further reduced when the thermal conductivity through the attachment components (like 2 girts) are considered.
Several recent research studies provide a better understanding of how heat transfer via thermal bridging impacts a building’s overall energy efficiency. One such example is the ASHRAE Research Project 1365 “Thermal Performance of Building Envelope Details for Mid- and High-Rise Buildings.” Click here to download the original report and also the ASHRAE Research Project 1365. A proper understanding of the thermal performance of the exterior wall assembly is critical to achieving proposed energy savings and project performance requirements.