Amelia Winters

Do you mean 50mm pir against the osb outer, then mineral wool to fill the rest of the void between pir and plasterboard?

Yeah. Im sorta thinking 95mm on the walls with no service voids and a combo of 95mm and 70mm on those that do - the 95 being in stud voids with no services, the 70mm with so at least the majority of the stud voids (all bar 2, maybe 3 of the voids on the external walls) would be 95mm PIR All of course cut slightly undersize and foamed into place and foil taped at seams / over studs & noggins. Sod trying to get PIR to an exact fit - tried that once. Nightmare. Someone told me "Cut your best and foam the rest" - so I guess that applies here too!

Thanks for all that - makes for some interesting results, some not what I expected but it's all good to know. My choice is probably the latter of them as its the simplest for me to do given how far finished the outside surface is already.

Perfect, thank you! I'll bin off the Acoustic roll and go with 70mm PIR and bust out the foam gun to seal it all up well. There will actually be two full walls that I don't need a service void in at all, so I'll go 90mm for them. That'll give me enough of a service void to avoid needing to batten the walls out where I need them. Would I be correct in assuming if I go PIR and seal it all with foam I can forgo the need for a vapour barrier sheet behind the PB, or is that still preferable? Size wise it's 3.2m x 4.6m, 2.4m to rafters. Floor is 120x47? joists, voids filled with 100mm pir & foamed, seams foil taped & 18mm marine ply over the top. Roof is warm roof, 18mm OSB3, Poly barrier sheet, 100mm PIR, 18mm OSB3 Walls are 45x95 on 400 centres, 11mm OSB3 sheeting outside, Tyvek wrap & counter battening for eventual cladding. One Window, One Door - Roughly 2.8sqm Glass area

Looking ideally to use it as a home office really, need an extra room that ideally isn't in the house for the kit I need for work to sit - so pretty much all year round use, but mostly in daytime hours. Not too concerned about noise, but would like it to not be fully acoustically transparent - mainly from outside noise sources as opposed to inside. Happy to compromise a little on thermal efficiency, it's going to be heat-pump heated as luckily the neighbour can install and commission them Thank you all for the advice

Thanks - it's proving a little more difficult than I first thought but getting there! Yeah there's WBA for the main deck and contact adhesive for the perimeter of it, 100mm worth if I remember right - got some kerb edge trim which will hopefully keep most from running down the fascia but opted for a layer of gravel around the base to try and reduce the splash back a little from it

Ok doke, thanks for the feedback. I wasn't set on Acoustic wool fully, my thought process was simply that with it being outdoors and next to neighbours that a wool product would provide somewhat of an acoustic layer to somewhat isolate outside noise - more than rigid PIR would anyway. I worked under the assumption (maybe wrongly) that rock/mineral wool is roughly 50% as efficient as PIR so would result in a similar performance to 50mm PIR. As I say though, very much anecdotal from what I'd read online and possibly incorrect. I will look into using 70mm PIR instead. Whilst I completely hate cutting the stuff it sounds like it would give me much better performance at the cost of acoustic transmission. Not building a recording studio or anything like that - but just something to block out the neighbours when they want to listen to music outdoors in the summer!

Hey! No, timber frame construction, OSB3 sheeting walls / roof, 18mm marine ply on a ground screw/frame foundation

So I'm building myself a garden room. In winter. Yes my timing sucks a little for that but it's keeping me busy. So far I'm at the following; Walls are timber (95x45 @ 400c), sheeted on the outside with 11mm OSB3 and Tyvek wrap and battoned for the eventual cladding that'll go on there. Roof is 47x175 @ 450c, 18mm T&G OSB3, Polythene VCL, 100mm PIR, 18mm T&G OSB3 - warm room construction (I've duct work to fit in the joist spaces, hence that choice). Walls are to be packed in the voids with 100mm Knauf Acoustic Roll insulation but I'm pondering my choice of straight 12.5mm Plasterboard, or 37.5mm PIR backed board for the ceiling and outer walls (there is an inner cupboard which I'll just use regular PB on, don't see the point in PIR backed for that). I'm swaying towards PIR backed. Yes it'll only be 25mm PIR, but figure that's roughly another 50mm of equivalent in the wool insulation, and gives me a little more depth to use 40mm boxes for sockets, data outlets and fibre stuff. I'm considering interstitial condensation, as I'm guessing I'd effectively be doing some sort of hybrid insulation style - particularly if I use that to board the ceiling? What's your thoughts - is it worth doing, even though it will cost more in materials? If so, outer walls, ceiling or both and should I still use a polythene VCL between it and the timber/wool layer? Apologies if this is a dumb question - I'm reading lots of different opinions on this and getting myself in a bit of a muddle over it!

Hi everyone, just saying hello - I'm Amelia, or Amy is fine I decided in September I'd give building a garden room a go. So far, so good. Walls are up and the roof is on..ish. Waiting for it to warm up a bit before I try and fit the rubber roof.. damn water based adhesives! I'll be probably asking some questions about plasterboard and insulation really. Got most of the other stuff nailed down - even managed to fit the door and window myself without making too much of a mess of it all. Hope to draw on some of your helpful selves soon :) Amy