GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

The $700 question

Stockwell | Posted in Energy Efficiency and Durability on

I want to beat a dead horse just a little bit more. The horse’s name is “Sill Sealer.” In our soon to be built house, the difference in cost of materials for sealing the 2×8 plate with the standard pink or blue foam vs. a 7 1/4″ x 1/2″ Denarco Sill Seal is $700. Is it worth it? Is there a reasonably priced alternative I am missing? I have looked at Protecto Wrap and Weatherbloc products and neither has a 7 1/4″ version, though Protecto will custom make one($$$$). The EPDM gaskets only go up to 2×6 size and would seem to lose their moisture blocking abilities if you used two smaller gaskets side by side.

Thanks in advance for any and all input.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. JC72 | | #1

    How about using foam along with a high viscosity fluid applied barrier on the exterior seam such a R-Guard or Poly Wall joint filler?

  2. jberks | | #2

    For what it's worth,

    I personally used the generic pink foam, mostly because my local lumber supplier didn't have anything fancy. I consider it a backup or a gap filler. where my primary seal is the fluid applied membrane at the exterior and interior joints of the sill.

  3. Stockwell | | #3

    I could use Prosoco R-Guard Joint and Seam filler on both the inside and outside seams for ~$300 plus my labor.

  4. GBA Editor
    Martin Holladay | | #4

    A lot of energy-conscious builders use Siga Fentrim tape (which sticks to wood and concrete) to bridge the crack between the mudsill and the concrete foundation. It's usually applied at the exterior of the building. I'm not sure whether it's less expensive than Denarco Sill Seal, but it probably is.

    The other approach for budget-minded builders is to use ordinary foam sill seal from the local lumberyard. Once the house is all dried in (so the weight of the building is resting on the mudsills), caulk the interior crack between the mudsill and the concrete with high-quality caulk (polyurethane or silicone).

    More Q&A threads:

    Sill plate flashing

    Air sealing sill plate while allowing permeability

  5. STEPHEN SHEEHY | | #5

    I don't think using an EPDM 2x6 gasket is a problem. Won't it still work as an air barrier?

  6. CMObuilds | | #6

    The expensive sill seal is a joke. The cheap foam gasket once compressed will form a good seal verified by blower door testing. Far more leakage will come from variation in the rim board to the mudsill, again verified by blower door testing and visually being able to see outside prior to sheathing hiding the gap.

    Spray foamed rims should get a shot along the top of exposed foundation and mudsill/sill seal to concrete joint as a redundancy.

    EPDM is great, but not necessary.

    I can get under .6 ACH 50 with lumber yard sill seal.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |