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I am in energy Zone 4 and have a stick frame home on an EPS ICF foundation built in 2007. The rim board is currently just insulated with batting and it is a little drafty and I a little worried that there is no moisture barrier between the basement air and the rim board (basement air-fiberglass bat-rim board-Tyvek). I am considering putting in 2" of spray foam to seal the rim board. However, my reading indicates that unless the outside sheathing is properly sealed to the foundation this can create more problems than it solves. In my case, there is no seal (no tape, no caulk) where the sheathing meets the ICF. The builder seems to have just run the Tyvek down below grade over the ICF moisture barrier. So there are two questions:

  1. Should one seal sheathing to ICF from the outside?
  2. How? There are plenty of videos of people effortlessly sealing sheathing to concrete walls, but I have not seen any of people sealing sheathing to EPS ICF. What products do you use?
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  • Is that seismic zone 4 or energy code zone 4 ?? – Lee Sam Feb 23 at 4:39
  • Energy, edited above. – TBP Feb 23 at 13:04
  • I have no understanding of "sealing sheathing". What's the purpose of that and how is it done? – isherwood Feb 23 at 14:13
  • I would be concerned with exterior sheathing in contact with the foam if moisture could get back there. On the transitions I have done with ICF I have used metal flashing. This helps in 2 ways it creates an air barrier and it helps stop wood destroying critters, it turns out carpenter ants love to nest in the exterior foam below ground. If you notice a bunch of fine styrofoam around the property contact a terminator and get them taken care of. – Ed Beal Feb 23 at 14:56
  • @EdBeal Do you have any pictures you can post? – TBP Feb 23 at 15:00

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