When a high r-value, above R20, is required in a pre-engineered metal building, one solution is a cavity filled insulation assembly in which the purlin and girt cavities are filled with batt insulation.
These systems use strapping and a vapour barrier installed to the interior side of the girts/purlins. The cavity is filled in batt insulation and the roof or wall is installed over top. With this system there is no compression of the insulation at the girts/purlins so the R value stays consistent throughout the building. Below is a chart illustrating this point.
These systems can provide R values in excess of R40, provide excellent condensation control, low flame and smoke spread ratings and an improved aesthetic interior appearance.
There are various manufacturer’s of these systems. Below are links to some of these products.