What is the R-Value of a precast wall panel? The answer of course will depend on the type and thickness of the insulation. It will also depend on the type of wall panel. The type of wall panel can help the system perform at a greater value than the insulation itself or it can make the system under-perform significantly compared to the material value. Understanding how the building is to be used and how it is to perform is key in determining what type of insulation and the panel type that is to be used.
In a composite panel the wythes act together. This composite action is typically achieved with solid areas of concrete and/or metal trusses. This can create thermal bridges in the panel, reducing its performance R-value. The thermal image above is an example as to how this happens. There are many cases where a panel with 3″ of extruded polystyrene is specified as R-15, but performs much lower due to the thermal bridging, approximately 60% or more.
In non-composite panels, the concrete wythes act independently. This design is used when high insulation value is required. The wythes are isolated by high-performance rigid insulation and are connected together solely by non-conductive connectors. This type of panel can perform at a R-value that is higher than the material R-value of the insulation. Companies, such as Thermomass, can calculate the wall panel performance by analyzing the building envelope.
The thermal performance of edge-to-edge insulated precast concrete wall panels with no or minimal thermal bridges maintains the R-values for continuous insulation as defined by ASHRAE 90.1-2010, thereby lowering energy costs. In some climates, increasing wall and roof R-values by as little as 5 can reduce energy costs by 5 to 20%.
For more information on R-values of precast wall panels contact us about our Lunch & Learn program.
Information provided by PCI and Edward Losch.