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Community and Q&A

Cellulose blown in insulation degradation

GibsonGuy | Posted in General Questions on

I’ve read where cellulose insulation can degrade much faster as compared to other types of insulation. As early as 15 years and has a life span of 20-30 years.  Yet most folks seem to recommend it over fiberglass. I can not get mineral wool in my area. My concern is that I plan on insulating a vaulted/cathedral ceiling, so unlike an attic, there won’t be an opportunity to add insulation years down the road.

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  1. CohesiveBuild | | #1

    I've worked in houses 100+ years old for 15 years, and they almost exclusively have used cellulose insulation successfully. I've never encountered a situation where the insulation was degraded due to anything other than rodents. One of the main concerns with fibreglass is its penchant for mold if it ever does get wet. Cellulose is better at water shedding and doesn't lend itself to mold very easily. If blown-in cellulose or mineral wool isn't available in your area what is? Only fibreglass seems crazy. Have you thought about doing a "hot roof" and using 2 lb spray foam?

    1. GibsonGuy | | #4

      Please see my reply to Malcolm. I am very pleased that I don’t need to worry about cellulose. I’m always second guessing what building techniques that I’m using. I am being extremely careful with the ceiling\roof details. I should also mention I am going to add another layer of polyiso on the bottom chord of the trusses, tape the seams, then fur out a solace so I can run my electrical and ultra slim LED lights between the drywall and the polyiso. Thanks for the reply.

  2. Expert Member
    1. GibsonGuy | | #3

      I’m happy with the replies to my question. As I can blow in cellulose for much less money and fiberglass batts were going to be very labor intensive as I have 24” deep parallel chord trusses and trying to fill in the webs was going to be difficult. I installed a standing seam roof with a 2” air space from eave to ridge. My site built baffles were made using
      1 1/2” recycled polyiso. Air sealing the baffles is going well, so I assume based on the replies, I need not worry about the degradation of the cellulose, which is great news. My source for the info provided in my post was a simple google search asking the life expectancy of various insulation materials. The info did not reference any studies in particular, which is why I posed the question.

  3. Expert Member
    BILL WICHERS | | #5

    There is a lot of bad info out there, unfortunately. Cellulose has been used as an insulating material for a long, long time, and it holds up fine if nothing else messes it up. Those "else-es" can be water from a leaking roof, or, more commonly, rodent damage. Don't hold that rodent damage problem against cellulose though, rodents can trash fiberglass too. I've replaced a lot of mouse-tunneled fiberglass batts in my own home as I gradually renovate and upgrade everything.

    The only issue I see with cellulose as attic insulation is that it is heavier per unit R value compared to loose fill fiberglass. I have some areas of my home I'll be adding additional blown cellulose to for this reason (existing loose fill insulation is also fiberglass). If I wasn't concerned with the weight, due to some marginal drywall I really don't want to replace, I would use cellulose. Cellulose is cheaper, and it's also better at blocking air movement in case you have any small air leaks you missed when you did your air sealing.


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