My lumber yard sent out their warranty guy who looked at 5 units I had water coming in on. It's been difficult to decipher. The building was open at wall insulation stage (no drywall and open truss to eaves). Window units had lightweight foam sealant applied to framing gap interior side. However, that foam by design doesn't fill well around shims if they protrude beyond the inner portion of the window (no foam in front of shim).Wow. I haven't installed kplbe in a few years since we fired Marvin. That's a concern- what are they doing to address?
We had high winds that may have blown water in. My subfloor got saturated in a few spots...that much water.
I don't have a good answer yet as the rep hasn't visited site. The high mullion was the most logical find on 1 window, but I had water in on fixed units as well.
We caulk left/right over housewrap, and tops. Then foil tape sides and top, upper HS folded over foil.
If the units are solid, it's got to be the minor friction air gap at bottom nailing flange to HW..where inner foam sealant didn't perfectly seal and allowed high pressure air/wind pull water in. If mulled units, potential poor exterior mullion and/or no sealant behind mullion and between the window jams.
I don't know how many windows I've installed over the years. I've never ran into this. Maybe I learn something.
Last picture, look closely you can see how much water is sitting on the inner sill over Tyvek.
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