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Most attics aren’t heated, but they must be insulated, including the actual loft hatch itself.
It’s pretty shocking work to be honest. Why go through the effort and expense of a loft conversion and not have it properly insulated.
Your designers really should have known better. It’s recommend getting a thermal imaging scan done (our RICS surveyor did this for us for about £300), because it seems likely that you have cold bridging causing damp. Rather than pulling things apart, get the imaging done and then target the areas actively losing heat.