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Community and Q&A

1950s insulation recommendation

user-7182223 | Posted in Energy Efficiency and Durability on

Looking for some recommendations pros and cons for a 1950s house, located in the Triad of NC. 

I’m looking to insulate the perimeter band joists in the basement (never been insulated). It’s sitting on a block foundation with 2 by 10 floor joists on 14 in center.

This home has had moisture issues that were fixed by a professional basement company with perimeter French drains and a sump pump. (Rarely turns on now that I fixed the grading, imagine that)

It also had a history of minor termite damage (profession company treated the perimeter of the foundation). I also had two applications of boracare mixed 1:1 along the entire inside perimeter.

With this in mind. I’m looking for the pros and cons for Batts vs open vs closed cell.

Thanks folks!

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  1. Expert Member
    Michael Maines | | #1

    Closed cell foam is by far the easiest and most reliable way to handle it. I avoid foam when I can but this is a case where it's a problem-solving material.

    If you want to avoid foam, and there are many reasons to avoid it, you can use any fluffy-type insulation, but you have to be very careful about sealing the interior with a variable permeance membrane. Few people have the patience to do a good job of it.

    There is no reason to use open cell foam at this location.

  2. Expert Member
    BILL WICHERS | | #2

    I would avoid batts, and I would avoid open cell spray foam here. Either of those two are likely to have moisture issues over time, which puts the band joist at risk. I would either use closed cell spray foam as Michael suggested (this is one of the niche areas for that product), or use canned foam to cut'n'cobble EPS panels into place tightly against the inside surface of the band joist.

    I would paint or spray on a protective coating to the framing prior to insulating this area. I used Coppercoat in my own home, which is a product similar to what is used to treat pressure treated lumber. There are also borate treatments that you can use. You might want to check with a termite mitigation contractor as to what treatment would work best to avoid problems down the road here before you start your project.

    Note that many areas where termites are a problem require you to leave an uninsulated "inspection strip" somewhere near the top of the foundation wall for annual inspections to catch signs of termites early before things get too damaged.


  3. Expert Member
    DCcontrarian | | #3

    Here's the concern: in heating weather, the air inside the house is going to contain a lot more moisture than the air outside. Any time you install insulation in a heating climate you have to have an air barrier and something to block water vapor, if you don't warm, humid air will work its way through the insulation and cause condensation on the cold side of the insulation, which leads to rot and mold.

    The joist bays are particularly vulnerable to this because their shape makes them difficult to seal. Batt insulation and open cell foam do not provide an airtight seal. Batt insulation often comes with a paper or foil facing that is meant to be an air and vapor barrier, but there's not really a reliable way to fasten it. Closed cell foam board works for this if you seal the edges with spray foam or even caulk, as does sprayed closed cell foam.

    1. Expert Member
      Michael Maines | | #4

      Open cell provides an airtight seal, as long as it's a few inches thick, but it's vapor-open so diffusion could eventually lead to moisture at the rim joist.

    2. user-7182223 | | #5

      Closed cell it is. I appreciate all the responses. Thank you folks.

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