Hello i have a single brick build detached garage at the back of my garden i have put in stud work at 75mm width for the walls with the intention of using kingspan but its biblically expensive so i was wondering what else i could use theres a semi permable membrame facing the walls followed by insulation (kingspan or not) followed by plastic non permeable membrame followed by plaster board i am using jablite 100mm for a floating floor and was going to use 100mm kingspan in the roof but i am trying to save money with the walls dont want to use jablite wondering if 75mm rockwool slabs are ok ? Cheers