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Community and Q&A

Insulating first floor of a plaster house

Jhorton1214 | Posted in Energy Efficiency and Durability on

We live in a 5A-6 zone on the Hudson Valley in NY – the house was built in the early 40’s…the house is essential one story which has plaster walls. We are converting the upstairs to a bedroom and bathroom with drywall.

I have read mixed reviews about adding insulation to the existing plaster walls. We would like to use fiberglass in the attic – drywall area and we were going to remove the siding and a couple sheathing boards to fish thru fiberglass on the first floor plaster walls. Is this a bad idea? Is there a better way of insulting plaster/drywall combination walls?

Any help would be appreciated.
Thank you

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  1. GBA Editor
    Martin Holladay | | #1

    I'm not exactly sure what you mean by "we were going to remove the siding and a couple sheathing boards to fish thru fiberglass on the first floor plaster walls." If you are thinking of inserting fiberglass batts from the exterior, that approach doesn't make much sense.

    The standard way to insulate empty stud bays in an older house like yours is with dense-packed cellulose. The insulation is installed through a hose. Installers drill one hole per stud bay. The work can be performed from the interior or the exterior; once the insulation work is complete, the holes are patched.

    Call up a few insulation contractors or weatherization contractors and ask if they are willing to install dense-packed cellulose in your walls.

    For more information, see How to Install Cellulose Insulation.

    -- Martin Holladay

  2. Jhorton1214 | | #2

    Thank you for the reply - And that won't create too much trapped moisture?

  3. GBA Editor
    Martin Holladay | | #3

    Whether your walls get wet depend on a variety of factors. The usual way water enters walls is from the exterior. (In other words, it's rain.) Wide roof overhangs and excellent flashing details prevent water entry.

    If your older house has skimpy roof overhangs and bad flashing details, it's certainly possible for your walls to get wet. It's hard for us to assess these details in a web-based advice column.

    Insulated walls dry more slowly than uninsulated walls, so good water management details are important.

    -- Martin Holladay

  4. Jhorton1214 | | #4

    Last question - should insulation contractors or weatherization contractors now about water management - or who should I ask about that?

  5. GBA Editor
    Martin Holladay | | #5

    Certainly insulation contractors and weatherization contractors should know about moisture management. But not all of them do, which puts you in a tricky situation.

    I urge you to educate yourself as much as possible. Read articles on GBA. Use the GBA search box to find articles on topics you are interested in.

    The more you know, the easier it will be to separate the knowledgeable contractors from the charlatans.

    -- Martin Holladay

  6. Jhorton1214 | | #6

    Greatly appreciate it.

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