It’s not unusual for a house to have three or four types of insulation: spray foam, loose fill, rigid foam, and/or batts. Each type has multiple uses, but most also have limitations on where they can be used.
The best insulation for each location depends on a number of factors, including cost, ease of installation, available space, and the material’s resistance to moisture.
All insulation types perform best when they’re installed well. Some (like batts and blankets) can lose significant R-value with even a slightly sloppy installation.
The Residential Energy Services Network (RESNET), a national association of home-energy raters, long struggled with the question of how to estimate the R-value of walls that vary widely in performance depending on the skill of the insulation installer. Eventually, RESNET developed a useful rating system for insulation installation quality. The system is described in an article published in the January/February 2005 issue of Home Energy magazine, “Insulation Inspections for Home Energy Ratings,” by Bruce Harley. The RESNET rating system recognizes three levels of insulation installation quality: Grade I, Grade II, and Grade III.
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Grade I is best
“In order to qualify for a Grade I rating, insulation must … ï¬ll each cavity side to side and top to bottom, with no substantial gaps or voids around obstructions (that is, blocking or bridging—as seen in the grade II photo below), and it must be split, or ï¬tted tightly, around wiring and other services in the cavity. In general, no exterior sheathing should be visible through gaps in the material,” Harley wrote. “Compression or incomplete fill amounting to 2% or less of the surface area of insulation is acceptable for Grade 1, if the compression or missing fill spaces are less than 30%…