Blown-in cellulose (settling)
I had 17″ of cellulose blown in between open-web floor trusses that supports a family room above an unheated garage. Recently I was installing a floor plug outlet in the family room floor and noticed that the cellulose depth was only 10-12″ deep max.
I contacted the installer, and to his credit he got back to me within a few days and is coming out to take a look.
My question is to what extent should cellulose settle, and how does one remedy this lack of insulation (also found a similar depth in another area while fishing for a buried wire).
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Settling of blown-in cellulose installed on an attic floor is normal. If properly installed, 13% settling is normal. If your average depth is now 11 inches, then your installer probably installed only about 13 inches originally.
What was the agreement? Was it to install a certain R-value? Or was it to install a certain settled thickness of insulation?
It's good that the contractor is coming back. Insist that the agreed-upon depth of insulation be installed.
For more information, see How to Install Cellulose Insulation.
The agreement calls for blow in of 17" of cellulose. Im sure one could argue that blowing in depth is not the same as settle depth. The installer did say that trying to get full depth would be a challenge, but having a depth of 10-11" is only 58-64% of what I paid for, and be confident that my home is insulated properly.
Experienced cellulose contractors are completely familiar with settling, and the phenomenon is explained on every bag sold. Each bag usually includes a table to help the contractor determine the installed thickness required to achieve a desired settled thickness.
If a contractor is aiming for 17 inches of settled thickness, the installed thickness should be about 20 inches.