A 6 star energy rating report specifies the performance requirements for your windows.
Minimum Deemed To Satisfy (DtS) energy performance requirements for the glazing U-value & SHGC are specified in Part 3.12.2. This means knowing the acceptable range of U-values for your building, requires following the Deemed to Satisfy (DtS) provisions. However, if you need to go beyond rigid DtS provisions and install cheaper windows, you need to use Performance Solution pathway for your building’s compliance. In other words, you need to undertake a Performance Solution instead of following NCC’s Performance Requirements. For instance VURB modelling is a Performance Solution for residential dwellings.