I am having a single storey extension built and the builder has used 100mm Knuaf Earthwool insulation in the cavity wall instead of 100mm Rockwool insulation as specified in the drawings. I am annoyed at this because I understand rockwool is a better product and has better R value, fire resistant, better sound insulation. Its too late to rectify as the wall has already been built. Approx 26 square meter has been used. How much should I be looking to deduct from the final account now that I have a deficient wall insulation that wont retain heat for longer.
Hi jazzq Probably easiest to ask your builder to increase the thickness of the insulation behind the plasterboard on external walls to compensate. Regards S
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