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When Cellulose Insulation is subjected to moisture or disturbed after being blown in, how is it affected?

We hired a contractor in Canada to replace insulation in our attic when a roof patch opened up under an ice dam in 2011. They removed batt insulation and replaced it with blown in cellulose fibre insulation. When they blew in cellulose insulation they did not connect the new bathroom vent hoses they supplied or seal pot lights below the vapour barrier and this is an extreme winter weather climate. This spring, the insulation was disturbed in order to determine the source of water causing damage to the drywall in the room beneath this space. They proposed removing the cellulose insulation by pushing it to the side in order to seal off the pot lights and connect bathroom vent hoses then scoop the insulation back into place.

Can you please provide answers to the following questions and give any advice as to how you would proceed?

1. With the moisture condensation experienced would the insulation r value be degraded even if it had not been disturbed?
2. If the R value is degraded due to moisture and being disturbed, how much R value would be lost?
3 How would you take this insulation out of the attic if it needs to be replaced?
4. What is the r value of cellulose insulation that is not blown in?
5. Would the insulation be subject to increased mold once it has been subjected to this much moisture and ventilation is not optimal?

Asked by Susan Bly
Posted May 19, 2014 9:47 AM ET


2 Answers

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You (or the contractor) should be able to determine whether the cellulose insulation is serviceable (or needs to be replaced) by looking at it. This requires common sense. If it is sopping wet or moldy, remove it and discard it. If it is merely damp or still fluffy, it should be OK.

I would be wary of this contractor's work. Failure to perform air sealing work before installing insulation is a big no-no. I would try to get their air sealing work verified with a blower door before any insulation is replaced.

Once the air-sealing work and fan ducting work is complete, and the insulation has been re-installed, it might make sense to blow a new cap layer of fresh, fluffy cellulose on top of everything. More insulation is better than less.

Answered by Martin Holladay
Posted May 19, 2014 10:27 AM ET


Cellulose is highly tolerant of moisture, but takes a long time to dry if it became saturated. Moisture cycling causes it to shrink slightly, causing it to settel, but once dry it's R-value is the same as cellulose at the (now higher) density & depth of material that had not been moisture cycled. If the cycling was below saturation levels it will not have any changes in appearance.

Cellulose that has been saturated then re-dried may become a bit clumpy/slabby where large chunks can be picked up in one piece if handled delicately. If it's too clumpy it may leave voids if just shoveled back in place, but that should be pretty obvious. Capping it with a blow-over as Martin recommends would fill the voids of mildly clumpy goods.

Cellulose that still contains a lot of moisture at sub-saturated levels can feel a bit damp to the bare hand, but will still flow freely between your fingers, with very little sticky/clumpy factor as long as you don't squeeze it together.

The mold & fire retardents continue to work even after repeated moisture cycling at non-saturating levels, but may leach somewhat if you have goods that have turned into nearly papier mache' rigidity. (Taking a chunk outside and testing it for flammability would be a good indicator as to whether it has become more mold-prone.)

Answered by Dana Dorsett
Posted May 19, 2014 11:34 AM ET

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