Grade 3 Insulation is considered a very low quality installation job based off of a 3 tier rating system originally developed by RESNET. Per the standards: Grade 3 shall be used to describe an installation with substantial gaps and voids, with missing insulation amounting to greater than 2% of the area, but less than 5% of the surface area is intended to occupy. More than 5% missing insulation shall be measured and modeled as separate, uninsulated surfaces
