1 year inspection found his duct for the HVAC has a lot of condensation. The builder said it was due to him running his 1/2 bath fan, however the exhaust for the fan is insulated 6" duct. I recommended the duct for the HVAC should have used insulated ducts. I don’t see how the builder’s explanation is possible any ideas?
Welcome Frank! Any pictures sure would help us to see what’s going on.
Is this a supply or return duct?
And, if your recommendation doesn’t work, do you step up until the problem is solved?
It is usually best to just report the illustration of facts not causation, per the SOP.
And, welcome to our forum…enjoy! 
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And what climate are you in?
this is a supply, and we are in Delaware I have some photos but not sure how to attach them?
Easiest way is to simply “Drag & Drop” or “Paste” them!
Is that actually moisture on the duct? Like, wet to the touch when the pic was taken of the open drywall?
Certainly the supply side should be insulated. I have never known non-insulated supply duct not to condensate.
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The specific room where the condensation issue is occurring wasn’t mentioned in the forum comment. If you have more information about the room, its location, or any other details, it could help in further troubleshooting the problem.
Key information is missing: are the ducts in conditioned space? Is it heat only or HVAC? Is there rust? What climate zone? What’s your local energy code say about duct sealing and insulation? How close are the bath fan and HVAC ducts?
Sooo many questions.