What are the room dimensions? Did you pay for 200mm of insulation? BC are there to ensure that the built structure complies with regs, and they aren't there to police what your builder did vs what he charged you for
That's not to say they haven't admitted liability in the past; we had a case on the forums where they'd signed off a roof that was way too flat for the tiles installed and was leaking like a sieve. The poster got money out of the BC, even though the builder had merely built what the architect had drawn. That might be a bit different to your case though, as the only thing you mentioned could end up in an argument where your builder says he put 200, your bc says he signed off 200, and you're left looking like you took 100mm out in order to pull a fast one..
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