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blown in cellulose a mold risk?

Zappo | Posted in Energy, Heating & Insulation on October 18, 2007 08:32am

Hello all,

I have a 1910 wood frame house in Maine with NO insulation in the walls.  My energy auditor is telling me to have dense-packed cellulose blown into the walls (and also add some over the fiberglass batts in the attic).  I would love to insulate the walls but don’t want to create a mold problem.  The walls still have the original plaster on them, and several layers of paint, but of course in 1910 they didn’t install a vapor barrier below the plaster and lath.

I have looked at buildingscience.com but am swimming in technical details.  Could someone convince me, in not-to-technical terms, that blowing insulation in the walls is a good idea and wont create a mold problem?

I would greatly appreciate it.  Thanks.

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  1. csnow | Oct 18, 2007 10:36pm | #1

    You are more likely to have a mold problem with the vapor barrier, since it will not always be on the right side of the vapor load.

    Dense pack helps keep moist air out of building cavities, where it would be prone to condense.

    I would suggest not burying that fiberglass in the attic without first pulling it up to look for bulk air leaks beneath.  Very rare that a home of that vintage would not have several square feet of air leaks into the attic space.  The FG will do little more than filter the air that leaks through it.  Look around wiring/plumbing penetrations, chimneys, wall plates.  Sometimes in older homes the tops of the stud bays for interior partitions are open to the attic.  This stuff is your low-hanging fruit.  Insulating exterior wall cavities is minimally beneficial when compared to the low cost of addressing typical leaks at the top of the structure.

    1. Zappo | Oct 18, 2007 10:56pm | #2

      That's reassuring csnow.  Thanks much.

  2. Piffin | Oct 18, 2007 11:57pm | #3

    I am in the midcoast area of Maine.

    IMO, it depends a lot on the condition of your siding package. I have seen a lot of older homes like yours where rot was encouraged by using cellulose. The cells will hold moisture just about forever once it gets wete.

    The argument goes - that if the cells are getting weet, you have a more serious problem to deal with anyways and it is not the fault of the cellulose.

    That it true as far as it goes.

    But where older siding has minor leakage, the air moving thru the walls with no insulation is venting things and helping dry the sheathing again such that wood that is occasionally wetted in the framing and sheathing is also regularly drying and ends up onuy showing water stains after fifty years or so. Then when the cellulose is added, the wood stays wet and things start to show advanced rot in ten years.

    The worst case of this I have seen is where somebody filled the walls with cells and resided the house, and then closed in a crawlspace where it had always been open to breezes built on piers as a summer house.
    They managed to capture all the ground moisture that had been venting out underneathe and force it to try to escape through the walls,
    Thepaint would no stay on the new siding and the sheathing under it was rotting within 8-10 years.

    So your decision depends on the weather proofing of the exterior and on how much heat energy you can afford to pay for. You need to consider the whole package and not just a couple features of your house.

     

     

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    1. JacktheRipper | Oct 27, 2007 03:51pm | #4

      I would think that most of the moisture trying to enter the wall cavity would come from inside the house in the form of vapor (if the external shell is sound). The vapor continues through the wall as vapor until it reaches the dew point temperature, where it condenses and does the damage as water. The vapor gets into the cavity by direct penetration of the wall, and by transport through air leaks. That's why a vapor barrier on the inside wall is needed, and why sealing air leaks from the inside is also needed. There are interior wall paints that purport to provide a vapor barrier for the wall, and caulking for air leaks around penetrations is a must. Controlling the vapor into your living space from the basement or crawl space is also needed. There are companies that specialize in this sealing process. It's more than just throwing loose plastic film in a crawl space, for instance.

      I had cellulose blown into my wall cavities in 1978 and it's been problem free (and really, really works as an insulator!). One inch holes were drilled in the exterior stucco every 16 horizontal inches at the top of the fire blocks and at the top of the wall, upstairs and downstairs. Holes were patched the same day, and the house was painted the next. House is in Orange County, California, and has little potential for mold problems, I suppose.

      Edited 10/27/2007 8:56 am ET by JacktheRipper

      1. Piffin | Oct 28, 2007 02:34am | #5

        Sometimes all you say is true
        Sometimes not.For instance here, if you take a house that had clap or shingle siding put on a hundred years ago, in this maritime climate, wind driven rain is highly likely to enter the siding and shell and the old oil paint will then keep it in.In your climate, dry and hot, you are fine. in a hot humid climate like the SE states,, the AC is keeping interior cool while the ext is hot and humid and wiul f=drive moisture in to ccondense in the interior face of the wall 

         

        Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

    2. JacktheRipper | Nov 02, 2007 01:58am | #6

      So, Zappo, some questions to answer:

      (1) Is your outside envelope well sealed against water intrusion, or could it be made so? If it's not, and the only reason you don't have a mold problem after 97 years is that you are leaking heat during winter so fast that it dries the wall cavity out, then any kind of insulation is problematic until you solve the water intrusion problem.

      (2) Is you house air conditioned? If not, then I re-submit that a vapor barrier on the inside wall and air-leak sealing from the inside is what's needed to protect vapor from entering the wall from the inside during the heating season, and condensing into water inside the wall as it chills down.

      In any case, sealing against air leaks is the single most important strategy for reducing water vapor into the wall cavity, whether it's coming in from the inside during the heating months or from the outside during cooling months.

      Final comment: the heating season in Maine is much longer then the summer cooling season, if any, so I would design for the winter months if it were my house.

      1. Zappo | Nov 02, 2007 02:56pm | #7

        Thanks much Jack,

        1) That is the crux of my concern.  Lots of old, cracked clapboards.  As the budget allows I am repairing and tightening up the exterior shell.  I may just resort to vinyl siding (ugh) but don't know if that will make things worse in terms of moisture buildup.

        2) A/C? Surely, you jest.  This is Maine after all :).  I have done LOTS of inside sealing (caulking, foam in the outlets,etc.) and will continue to look at possible leaks.

        Thanks for your solid advice.

         

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