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Community and Q&A

Blown-in cellulose condensation risk?

Seth Rutledge | Posted in Energy Efficiency and Durability on

So what is the final word on blown-in cellulose insulation in a pre-existing wall? I have plaster walls on 2/4s with wood board sheathing wood siding and shakes on the outside. If I blow in insulation will condensation form on the outer wall causing mold and paint peeling?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Seth,
    The house you describe will perform fairly well when insulated with cellulose. The cellulose will go a long way toward reducing air leakage, and will add R-value to the walls. Cellulose does a good job of buffering swings in humidity content. The wall will dry readily in both directions: through the plaster to the interior, and through the board sheathing and wood shingles to the exterior.

    That said, any time that you add insulation to the wall of an older house, it's probable that your exterior paint won't last quite as long as it used to. The main reason is that the insulation keeps your sheathing and siding a little bit colder than they were before. You are no longer losing as much heat through your walls -- and before the insulation job, that leaking heat helped keep your siding warm and dry.

    Most homeowners conclude that the benefits of insulation far outweigh the disadvantages.

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