Insulation

can 100mm polystyrene sheets serve as cavity wall insulation instead of rockwool?

Anonymous user 23/02/2024 - 3.00 PM

Hi - I have a build about to start and my builder is wanting to use Rockwool slabs in the cavity wall. I have read that Rockwall or mineral wool can sag and even act as a straw to bridge the wall and create damp - and - once damp actually reverse the insulation and make the house colder. I expressed my worry to the builder but he said he has never had a problem. Hoever - Im still worried about the rockwool touching the outside wall and bridging the cavity. So... My gut feeling is to buy Celotex type product as boards which are foil backed/vapour barrier but they are twice the price. However - my research has led to me wondering if Polystryene boards are of use. I do understand the insulation quality will be less than celotex initially. Can it be used? Eg - something like this: http://www.wickes.co.uk/Wickes-75mm-General-Purpose-Polystyrene-1200x2400mm/p/210825#tab-reviews_content