Construction was underway on an energy-efficient home extension, when the builder advised that he was having difficulty meeting the architect’s insulation specification. As designed, the building had many energy efficient features: good sun orientation, careful management of solar access into the conditioned space, high quality double-glazed windows in the conditioned area, non-conditioned airlocks for the front and rear entrances, and lots of insulation in the floor, walls and ceiling. As designed, the extension (a separate wing from the existing building) was rated at 6.6 stars.
However, the 90 mm stud walls had insufficient depth to accommodate the thickness of insulation needed to achieve the architect’s specified R rating; using standard insulation materials that did fit would reduce the thermal performance of the building, something the owners of the building were loathe to do. The builder had identified some alternative insulation products which provided higher R ratings within the 90 mm thickness constraint, but all were much more expensive that the standard product the builder had allowed for in his price.
FirstRate5 was used in an iterative manner with the builder to explore alternatives. The builder was able to source double glazed windows for the airlock areas which were the same cost as the windows originally allowed for; these windows did not perform as well as those selected for the conditioned areas, but were more affordable. Experimenting with different insulation schemes in FirstRate5 found that using standard insulation materials in the externals walls of the airlocks and between the airlocks and the conditioned areas, while using the bare minimum of expensive high performing insulation only in the walls between the conditioned areas and the outside increased the modelled performance of the building to 7.0 stars - an outcome with which the owner was very happy.