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The home is new construction on the beach front in Galveston. The wall is 12' high by 52' long.

From the outside in, it is Hardie lap siding, house wrap, 5/8 plywood, 3" closed cell foam, 5/8" plywood (sheer wall strengthener), and half inch drywall and paint.

On the outside I have calked under each siding board. The foam takes up 3" of the 8" cavity (wall is 2X8) so i have a void of 4 to 5 inches. The wall is blocked every 48". Plate windows take up 3/4 of the wall. The windows are impact triple pane units with a low E.

I don't know if the foam is putting off a chemical that is softening the plastic covers, a heat build up in the wall... I have removed all of the plugs and calked between the drywall and the wall plug. Checked each to see if poly sealed where the wires enter the box and all were sealed.

I have even had mildew grow under the plate. Some of the plates had moisture on the back side before I re-caulked the outside and repainted. I have put all new plates (plastic) on with a foam gasket behind each. they still are bowing. I have had air specialists (2) inspect the home and they can't figure it out. The A/C units are 19 SIER Heil v speed units that pull the moisture out of the house. The remainder of the house is open cell foam.

That's my story. Any ideas short of pulling the S/R and plywood off the inside wall and filling the remainder of the cavities with foam or bat. I have expensive wood treatments around each window that has already been removed and poly sealed between studs and trim 2 weeks ago. Moisture content in the poly sealed area is high and in the 20's in the wall cavities. Scratching my head.

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    This is an issue that should be addressed with your builder. It sounds like a strange phenomenon and may indicate a serious problem. (Plastic plates should not bow due to moisture or mild heat.) We're not your best resource.
    – isherwood
    Aug 14, 2020 at 14:55
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    Also, stop arbitrarily caulking things. Your siding should not be caulked except for the ends against the trim. You're going to cause moisture buildup and buckling, potentially voiding the warranty. It's probably ugly as heck, too.
    – isherwood
    Aug 14, 2020 at 14:58
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    A photo or two of the plates would do wonders. Revise your post and use the editor toolbar.
    – isherwood
    Aug 14, 2020 at 15:02
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    Caulk under the siding boards is a mistake - moisture will get into the wall and it can't dry to the inside because of the closed cell foam. I'd consider removing that caulk. Can you show a picture of the bowed plates?
    – Greg Hill
    Aug 14, 2020 at 15:17
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    You said you calked around the boxes and there are poly seals Could you explain this what was used to seal the boxes and why? Plastic plates with foam gaskets? I think you might be causing some of the problems. A photo of the issue and a photo of what was used to seal the box might be helpful.
    – Ed Beal
    Aug 14, 2020 at 16:31

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It appears the wall cannot dry out either to the inside or the outside. I question the use of closed cell foam in the wall and do not think you should add still more without careful consideration.

You built a superinsulated house that was strongly built to resist hurricane force winds in a warm humid climate. You got a wall which traps moisture inside. The blocking every 4 ft is going to make it difficult to dry the inside without removing all the drywall and the sheathing inside. Then you will have to figure out how to insulate the wall in such a way that it can stay dry.

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  • Anything happening on this moisrure trapping wall? Have you considered putting vents inside that would allow dry inside air to circulate inside the wall between the inside of the interior wall and the foam? Sep 14, 2020 at 20:04

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