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Retrofit Wall Insulation Options

gcv | Posted in Energy, Heating & Insulation on May 4, 2009 10:32am

Hello:

I have a wood-framed house built in the 1920’s. The inside walls are lath and plaster. The outside siding is 6″ wood lap. I want to insulate the 2×4 walls, and am trying to find the least destructive and most effective way to add insulation. The paint primer on the inside wall surfaces is an acrylic vapor barrier. I did this because the walls don’t have a visqueen or foil vapor barrier inside them.

I’m concerned about moisture building up inside the walls and rotting the wood, so I’ve been hesitant to blow insulation into the walls. I think with the vapor barrier I should be OK. 

I’m leaning towards having someone blow cellulose into the walls from the outside, after they remove a row of lap siding and cutting holes in the outside sheathing. I think this would be cleaner and easier than cutting and patching the plaster walls on the inside. From what I’ve read, it seems like cellulose doesn’t settle and compact as much as fiberglass.

Is blowing in cellulose from the outside the best option for me?

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  1. User avater
    mmoogie | May 05, 2009 12:47am | #1

    I thinks so. But only if you can find someone who knows how to dense-pack the cellulose to at least 3 lbs/cf.

    1. BilljustBill | May 25, 2009 05:41pm | #8

      A question to solve my curiosity...  If you dense pack cellulose or fiberglass in existing enclosed walls, how do you prevent the drywall from popping away from the studs or prevent it from cracking the drywall?

      Thanks,

      Bill

      1. User avater
        mmoogie | Jun 06, 2009 09:48pm | #9

        >>how do you prevent the drywall from popping away<<Sorry for the delay in responding. Missed this one apparently.Anyway, I've not had a problem with blowing sheetrock or plaster off the wall. But I use a pretty healthy screw schedule on my sheetrock. I use double screws every foot on 5/8 rock for ceilings, and single screws every eight inches on 1/2" rock for walls. I've seen rockers go as light as every 16" on walls though, which could be a problem.I did have some mold-resistant sheetrock blow off a few weeks ago though. I won't use that garbage again.Steve

  2. hmj | May 05, 2009 12:55am | #2

    Yah,

    least destructive. Being that it is balloon framed, they might be able to access a lot of the stud bays from the attic, except under windows, but then you can't get a dense pack. You want it dense packed so it air seals the leaks in the envelope.

    1. User avater
      mmoogie | May 05, 2009 01:02am | #3

      I've successfully dense-packed ballon-framed walls from the the attic. The roofing nails are mighty hard on the pate though.

      1. hmj | May 05, 2009 01:22am | #4

        I figured it was too much going from the the 2nd floor top plate down to the sill. I've seen blowers come in from the attic then cut holes under windows and such, to get in under the headers..

        1. gcv | May 05, 2009 04:05pm | #5

          Thanks all.

  3. Jay20 | May 06, 2009 05:18am | #6

    There are a few companies that specialize in foaming existing structures. Someone in a past discussion gave a web site of a national firm that does this. I would at least explore this option also.

  4. reinvent | May 25, 2009 04:21pm | #7

    Look into this as well.

    http://www.retrofoam.com/

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