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Best way to improve 2×4 stud wall air sealing in 1960’s house ?

mike78 | Posted in Energy Efficiency and Durability on

A friend is renovating the living room in a recently purchased house that was built in the late 1960s. Location is in the mountains of Virginia, climate zone 4. The exterior wall construction (outside to inside) is: Horizontal lap siding, diagonal board sheathing, asphalt felt paper, 2×4 studs with kraft faced fiberglass batts, interior plywood paneling.

My friend is removing the interior paneling, partly because there are no protective metal plates over the wiring routed through studs. He plans to add protective plates then cover the walls with drywall. The original fiberglass insulation is installed with the kraft backing loosely stapled along the sides of the studs, not lapped over the stud faces.

The wall construction does not have an effective interior vapor barrier. I dont know if the asphalt felt paper represents much of an exterior air barrier. My guess is that the wall is quite leaky and could be improved since the interior paneling is being removed and the insulation will be exposed.

What is the best approach for improving the wall ? Is it safe to add a 6 mil poly vapor barrier across the studs before installing drywall ? Is there any advantage to reinstalling the paneling, then putting drywall over it ?

Thanks for any advice.


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  1. GBA Editor
    Martin Holladay | | #1

    This wall does not need an interior vapor barrier. For more information on vapor barriers and vapor retarders, see these articles:

    Vapor Retarders and Vapor Barriers

    Forget Vapor Diffusion — Stop the Air Leaks!

    Do I Need a Vapor Retarder?

    It's important to pay attention to air sealing, however, and now that the walls are open, your friend has a good opportunity to address airtightness.

    If this were my house, I would remove and discard the old fiberglass batts, which are the worst imaginable type of wall insulation.

    For better performance and reduced air leakage, the stud bays can be filled with spray foam or dense-packed cellulose. If your friend chooses dense-packed cellulose, it might be a good idea to follow the Airtight Drywall Approach.

    If your friend chooses to install fluffy, air-permeable insulation, it's worth considering the installation of one of the sprayable caulk products. For more information, see Air Sealing With Sprayable Caulk.

  2. charlie_sullivan | | #2

    Not your question, but I'd also consider making the walls 2" thicker for more insulation while you are at it, if he doesn't mind losing a little space on the interior.

  3. mike78 | | #3

    Hi Martin and Charlie,

    Thank you for the information. Would damp spray cellulose also work in this case ? Contractor applied insulation may not be an option due to cost. How about Roxul mineral fiber batts ? I used Roxul batts on a small insulating job and they seem much denser then fiberglass.

    I have not seen the walls yet but plan to visit this weekend. I was surprised that asphalt felt is the visible layer on the exterior side of the existing fiberglass batts. I expected 1960's construction to have some sort of sheathing, either plywood or diagonal boards. We are assuming that diagonal board sheathing is on the outside of the asphalt felt. If so, it seems strange to have asphalt felt between the studs and sheathing. Perhaps there is no sheathing and the walls just have diagonal bracing. I will know more after I see it.


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