re: Issues with new insulation

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Hopefully you can find someone who has a background in building science whether in your AC guy or insulator or just finding an independent guy.

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This is definitely what you need - residential building science forensic investigator that deals with these problems daily - what is happening to you not an uncommon occurrence in hot, humid regions when older homes are retro-upgraded with roof spray foam attic insulation after the fact. If you were in New Orleans or Atlanta I could suggest someone who does this. No doubt there are numerous people in Houston available to help you. You are looking someone like these guys - I mention these two b/c I own their books & have read them - neither are in your area. Nate the Hose Whisper and Allison Bailes - Energy Vanguard . This guy in New Orleans Paul LaGrange LaGrange Consulting . LaGrange has a weekly radio program on WWL and he takes at least one call weekly in summer from a person dealing with the same issue you are experiencing post spray foaming an attic.

Turnblad85 has perfectly described the psychometrics of what is occurring relative to the large change in dew point temperature in the attic with the upgrade in insulation. And as others have stated it’s my understanding the attic envelope should be fully incapsulated including the soffits. It does appear to me reducing humidity in the attic via dehumidification to reduce dew point temperature would help.

Another thing to consider/be aware of - if your 6-tons of HVAC was properly sized for the home before you spray foamed the attic, then you are very likely considerably over-sized in HVAC tonnage now that you have reduced the heat load on the house - this assuming both units are single stage, and not multi-stage systems that adjust for the heat load in the house. Don’t go buying new multi-stage HVACs until an expert who knows what they are doing can investigate and provide the proper solutions to fix the issue. Like in automotive repair - you need a good diagnostician to ID the issue(s) & not just a parts changer.