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Final Checklist Before Installing Basement Insulation

thegiz | Posted in General Questions on

As always thanks for all the advice on this forum it is greatly appreciated. Ready to take the information I learned on this site on another project and just want to check some final details. Again my situation is old home, rubble foundation with parged concrete coating, house in westchester county NY

1. On most walls I’m attaching 2 inch eps with foam adhesive and taping the seams with red tape or whatever it is called. They have that at box stores?

2. I’m using 1×4 furring strips where possible to save room. I’m leaving the furring strip 2 inches from bottom of wall. I have 2 walls that I need to make as thin as possible. What is the absolute thinnest I can make the wall without sacrificing mold risk.

3. I’m insulating exterior walls that intersect interior masonary walls that I’m not insulating. So an inside corner that will come in contact with concrete. How do I detail this so the corner wont develop mold. Can green board touch concrete or do I need to close it off somehow?

4. Finally do I need to waterproof the walls with something like Drylok before attaching foam or is this pointless. I will probably at least Drylok my interior masonary walls that are not insulated.

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  1. Expert Member
    Josh Salinger | | #1


    1. You will just want to make sure the tape is compatible with EPS and is vapor closed. There is a great discussion along with some tape options here:

    2. You will want to make sure you are meeting code in your area. This will determine the thinnest wall you can install. I think you are in CZ 4A? If that is the case, R-15 is required in basement locations. You may want to look into a product such as Insofast basement panels: We used them in conjunction with 1" of GPS insulation to meet the R-15 requirement here in PDX (CZ4C). The nice thing about these is that you can skip the 1x4 and attach the drywall directly to the foam. This may be the thinnest application you could do.

    3. I'm not sure I'm following you exactly... I would have the insulation go all the way to the corner and then you could furr out the interior walls to attach the gyp. to. You could also use the insofast on these interior walls as it would break the thermal bridge. I would recommend using a fiberglass faced gyp. product such as Dens Armor Plus in lieu of 'green board' I have seen plenty of mold on green board in my day. Don't give the mold food in the first place. You will have to skim coat the entire wall of the Dens Armor as the paint will otherwise flash at the mud joints.

    4. It is pointless. Products such as Drylok are bandaids at best. If you detail the wall correctly and stop the vapor drive you will stop any issue that Drylok claims to solve.

  2. thegiz | | #2

    Thanks for advice. I can't find densarmor plus. Is there something they sell similiar or is there a place I can find densarmor?

    1. Expert Member
      BILL WICHERS | | #3

      You may need to check with a commerical building materials supply house. Densarmor and Densglass are non-paper faced gypsum board products that are very common in the commercial world, but much less common in residential construction. This basically means you probably won't find them in box stores (but the box stores can probably order them), but the commercial supply houses will often have them in stock.


  3. Expert Member
    Josh Salinger | | #4

    One should be able to procure it from a local drywall distributor. A quick google search found it available at Home Depot, although I'm sure it is stocked in some but not others. A local drywall contractor may be able to connect you with a supplier, too. I'm not aware of other brands off the top of my head, but I'm sure they exist.

    1. thegiz | | #7

      Found it at a local drywall supplier but it took some searching, thank you

  4. Deleted | | #5


  5. thegiz | | #6

    Also is everyone in agreement with Josh, Drylok or waterproofing under rigid foam is pointless

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