The wet cellulose insulation recently installed in my home's walls has settled in some spaces. Why?


The wet cellulose insulation recently installed in my home's walls has settled in some spaces. Why?

Asked by Heath

I am building a new home and hired a insulation contractor to put wet cellulose in the walls. The cellulose settled in some spaces. The cellulose was installed and by the following day it settled in 14 stud space throughout the house. It seemed to stop settling about 3 days later. I was curious about why some spaces settled and other never did so I tried to push down from the top of the cellulose that didn't settle. I couldn't budge the cellulose it was so dense. When I put my hands on top of the cellulose spaces that settled about 2 to 3 inches I could compress them about 3" before I couldn't push it down any farther. So I stuffed them as full has I could get them with fiberglas on top. A couple days later and the insulation stayed the same with the Fiberglas stuffed on top. So they drywalled the walls. I hope the cellulose stays the same has it is now.

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Michael Holcomb's picture


Thank you for the question and the great images showing the type of settlement problem you are experiencingwith your cellulose wall insulation.

I am including two similar images (below) so you know that this is a fairlycommon problem with this type of insulation system.

Let it dry out

Cellulose insulation is hygroscopic, meaning that moisture is dispersed throughout the material preventingwater from accumulating in any one area.

  • Cellulose insulation is able to hold many times its weight in moisturewithout reaching its fiber saturation point. This added weight can lead to settlement.
  • Wet spray cellulose shouldnot be sprayed at more than 40% relative humidity.
  • Under the right conditions it may dry to 11% RH within 24hours.

While additional settlement is possible it isn't likely if the insulation was allowed to "dry" out before it wascovered.

Cellulose was a good choice

You made a good decision to go with cellulose insulation for your wall system. Its density will reduce convectiveheat transfer outperforming fiberglass blanket or spider systems.

Repairing the settled cellulose by stuffingfiberglass into the gaps allowed you to move forward without significantly reducing the performance of the wallinsulation system (we are talking a minimal percentage of the overall wall system).

So rest easy; this problem is not worth worrying over.

The General

For more information:

Read Lily Livingston's Q&A "Doesn't sprayed cellulose insulation tend to settle, leaving areas in the wall where there is no insulation?"