For decades, misinformation has swirled around how much cellulose insulation settles. The "myth" of exaggerating the settling of cellulose insulation was probably initiated in the 1970s by industry competitors and has continued to propagate in online posts and offline articles through the present day. The fact is, some minor settling naturally occurs in all loose fill and even batt insulation products. However, manufacturers for years have been required to provide clear information for their insulation products to account for this minor occurrence.
Back in the early 1970s, the entire insulation industry, including fiberglass, was loosely regulated. This changed in the late 1970s and early 1980s when standards were adopted to regulate insulation manufacturers and their products. One measure that was taken required all cellulose insulation manufacturers to include coverage charts on their product bags for "installed" thickness and "settled" thickness. This simple change addressed the concerns with settling providing a factual calculation contractors and consumers could expect to achieve desired R-Value or thickness.
The reason for this modification is that once insulation is blown into an attic, the material will naturally take two to three days to reach its final density. A slight difference in the thickness will occur as the cellulose attic insulation settles into place. As can be seen from the examples provided here, the change in depth is minimal. For example in an attic insulated to R49 (R-Value) the cellulose insulation material will settle about an inch and half. Industry, as well as internal Fiberlite research, suggests this occurs within the first 48-72 hours after the material is installed into an attic.
Since FTI started manufacturing cellulose insulation in1985, this standard has always been in place and coverage charts printed prominently on all product bags sold. When installed properly to the indicated depth on the bags, consumers can rest assured the final R-Value will be achieved providing high energy efficiency and savings for the life of the dwelling.