Liquid-Applied Air Barrier on Rim Joists
Hi, I would like to air seal the rim joists in my 100 year old house with Visconn and Visconn Fiber. How thick does the Visconn need to be in order to air seal effectively? And would this create any potential problems with moisture, mold, wood rot, etc? After applying the Visconn to air seal, the plan would be to insulate with mineral wool batts. One other thing: there is currently mineral wool batts in the rim joists with no air sealing. The insulation contractor refused to air seal unless I was purchasing closed cell spray foam as both insulation and air sealing. Is the mineral wool by itself a potential moisture issue?
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Just checking in on this again. Does anyone know how thick Visconn needs to be for rim joist air sealing? Has anyone ever used it? I can’t find any insulation contractors who are willing to do so (they will only either air seal with closed cell foam or just not air seal at all).
It sounds like you are trying to avoid using foam, is that correct?
The typical approach to insulating and air sealing rim joists use either spray foam or rigid foam://m.etiketa4.com/article/insulating-rim-joists
The comments in this thread about foam-free rim joist insulation might give you some places to start, especially the comment from Malcom Taylor://m.etiketa4.com/question/insulating-rim-joist-without-foam
Using Visconn to air seal the rim joist seems like a fine approach to air sealing at the rim joist. I would expect the thickness to be specified in the manufacturer's installation instruction or specifications. Is it not? If you insulate with mineral wool, the challenge will be to create an air tight vapor retarder on the interior side of the mineral wool. That sounds tricky, which is why it is an uncommon approach. But where there's a will there's usually a way ;)
The air barrier needs to be continuous to have real affect, otherwise air will find away around and through assemblies.Sealing your rim joists is great, but the sealing system should tie into a continuous plane of air tightness.
If you have a continuous air barrier on the outside of the house, your interior vapor barrier/retarder does not need to be air tight. Think a sheet material stapled up but not taped or caulked at the edges or penetrations.
Am I understanding the situation correctly?