Grade 1 insulation is considered a high quality installation job aka one with very minor defects based off of a 3 tier rating system originally developed by RESNET. Per the standards: Grade I installation requires that the insulation material uniformly fills each cavity side-to-side and top-to-bottom, without substantial gaps or voids around obstructions (such as blocking or bridging), and is split, installed, and/or fitted tightly around wiring and other services in the cavity. It all requires that it is in encapsulated /direct contact on all 6 sides with an air-barrier with a few exceptions(attics, rim joist…) Compression or incomplete fill amounting to 2% or less, if the empty spaces are less than 30% of the intended fill thickness, are acceptable for “Grade I”.
