In the energy modeling of a building envelope, which of the following U-values should be...

The assembly U-value of a building envelope component is the overall rate of heat transfer through that component, taking into account the different materials and layers that make up the component. For example, the assembly U-value of a wall would include the effects of the insulation, framing, sheathing, cladding, air films, etc. The assembly U-value is different from the material U-value, which is the rate of heat transfer through a single material. For example, the material U-value of steel is much higher than the material U-value of glass, but the assembly U-value of a steel-framed window may be lower than the assembly U-value of a glass curtain wall, depending on the other factors involved.