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  1. #1
    Join Date
    Mar 2008
    Posts
    6

    Default Moisture on my Cellulose Insulation

    My house was built in 1946. When I bought it a few years ago it had very little insulation in the attic. The attic is very tall and the roof slope is very steep, so with time I am planning on expanding the living space into it. Due to shortage of materials following the war, the rafters in the attic were all different sizes and the sparse insulation was mostly missing. Since I bought the house I have installed 2x10 rafters to support future floor. I also cleaned out all of the old insulation and filled all of the rafter bays with cellulose insulation. It worked like a charm. I was able to fill in all of the irregular cavities with cellulose and the whole house is much warmer.
    About a year later I wanted to store some stuff in the attic, so I put plywood across the rafters and stored all of my junk there. After some time I noticed that the plywood is getting moist on the underside, so much so that some mold started to grow on it. I immediately removed it and replaced the moist cellulose under the sheets of plywood.
    I am not sure where all that moisture is coming from and what I could do to prevent it from accumulating on the plywood sheets. I researched the cellulose insulation, and no moisture barrier was recommended, so I did not install it. The roof has eaves all around, so the attic space is cold. I filled the bays with cellulose all the way to the rim. Should I have left an inch of space between the top of cellulose and the plywood?
    What should I do to make sure that my house is properly insulated and that I can continue with the future expansion into the attic?

  2. #2
    Join Date
    Mar 2009
    Posts
    1,387

    Default Re: Moisture on my Cellulose Insulation

    Howdy, Eves have any venting into the attic? Any roof vents to exhaust air? It sounds like you have condensation forming in the attic and to resolve this you need to vent it. Installing eve & roof vents to let moisture laden warm air out instead of allowing the moisture to reach dew point and stay in the attic.
    The cellulose is not to have a vapor barrier to allow the vapor moisture to flow out thus drying it and not causing wet rot to the framing members.

  3. #3
    Join Date
    Mar 2008
    Posts
    6

    Default Re: Moisture on my Cellulose Insulation

    The roof does not have a ridge vent at the top of the roof. But the attic space has windows and those stay cracked open. It seems to be enough to vent the attic and cool the roof. I do not get any condensation on the underside of the roof deck. It is perfectly dry. The whole space is dry with exception of the underside of the plywood.

  4. #4
    Join Date
    Mar 2009
    Posts
    1,387

    Default Re: Moisture on my Cellulose Insulation

    Howdy how high do you have any humidifier set in the home during the winter? Do you have exhaust fans in the baths and run then 15 minutes after showering ...

    Any ceiling penetrations holes in the area under the plywood if so use spray can insulation and plug them to retard moist air flow into the area.

  5. #5
    Join Date
    Mar 2008
    Posts
    6

    Default Re: Moisture on my Cellulose Insulation

    I don't have any holes in the ceiling under the plywood.
    I don't have a humidifier and I do have a bathroom vent that is vented to the outside. The vent and the venting tube are both insulated so I don't have any moisture coming from the bathroom.

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