Just about to start planning the interior insulation for my garden room walls. Studs are 4x2 (95mm). Would there be any kind of advantage to acoustic levels, if I was to put 50mm pir tight against the osb and then squash in 50mm of rockwool acoustic wool/slab, with plasterboard and skim on top of that. Working it out, it wouldn't cost much more than putting 90mm pir straight in. If there is no big effect on soundproofing, when adding the acoustic insulation, I may just go pir only

