How Much Does Cellulose Insulation Shrink Over Time?

The Facts

• Cellulose does not remain at a set volume forever. It shrinks and settles over time, losing up to 25 percent of its total volume compared to when it was first installed. This is due to a number of factors, including moisture loss and redistribution of its component parts over time, a process called “settling.”

Settling

• Settling is the result of cellulose insulation being either loose-fitted or sprayed into the area being insulated. Cellulose insulation is not a roll or blanket insulation material; it is instead a collection of particles that together form an insulating barrier. As a result, the particles will move over time until they are more evenly distributed, which reduces the overall volume of insulation by up to 25 percent.

Moisture

• Because the majority of methods for installing cellulose insulation involve spraying in damp cellulose so it clings to the surface to be insulated, the volume of insulation falls as the cellulose dries — and thus shrinks — over time. This can reduces the volume of cellulose insulation by up to 20 percent.

Effects

• A lower volume of insulation reduces the amount of insulating power, so more heat is lost from the building. The combination of settling and moisture loss means a significant portion of the insulating ability is lost due to shrinkage. In addition, cellulose insulation can absorb moisture over time, which reduces its insulating ability even further, and also risks fungal growth in the insulation.