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What is the best brand/product for maximum acoustic performance for insulation between 2x4 400mm studs and joists? I'm looking at all sorts and it's starting to get a bit confusing as so many difference varieties: slab, rolls, densities, rigid on one side, loft, cavity, etc. I've seen on some threads that people say it doesn't really matter and you can stick loft insulation in-between the studs? I'm thinking 100mm everywhere. just cram it in all over the place. But some people have said you must have an air gap to improve performance. Is Rockwool RWA45 any good? It's £30 per roll of 2.88sqm. It's 600mm wide though when really for ease and speed of installation I should be going for 400mm slabs shouldn't I? There is another Rockwool one: Rockwool Sound Insulation Slab - 100 x 400mm x 1.2m This is a different model but what is the difference?

After reading every post on this forum on the subject of sound insulation and in particular Rockwool I wanted to document our experience. Until the delivery arrived and we opened the packets we really didn't know what we were going to be working with. Here is the best description I can give. We ordered the following from Insulation4Less. They told us the lead time was about 4-6 weeks (nationwide shortage) but actually it all came within a week leaving us with a literal mountain of rockwool to store around site. It was wrapped but needed to be lugged into the house out of the rain. Big job. The 50mm deep packs were orginally intended to go in the ceilings where there were lots of pipes to fit around. We chose RWA45 rather than the more expensive Flexi. Having not seen the Flexi I can't give a really accurate comparison. But the RWA45 is flexible and can be pushed into spaces and compressed a little anyway. And it is cheaper. It is not rigid / solid like Celotex (which I had first thought it might be). Here are some open packs. It is pretty easy to cut using an insulation saw like this. https://www.screwfix.com/p/bahco-insulation-saw-22-560mm/7498k But it does shred easily too. Mask and gloves absolutely essential. The 100mm deep stuff looks like this. So although it comes in these "batts" which have a form to them, you can trim to to the size you need. We are trimming almost everything because the 600mm wide batts don't fit into the 560mm gaps between the 600mm centred studs. But there are plenty of places to stuff the offcuts and the puzzle of how to use every offcut as efficiently as possible is keeping us both amused somewhat. We are fitting this into all the stud walls (internal) and the ground floor ceiling. No need for any insulation on the external walls or top floor ceilings as that has been pumped in by MBC (more of that in another blog). Hubby used our MVHR builders straps to fit up a load in the ceiling. He is now using cheap pallet strapping and a staple gun! It is fair to say that we have been doing this sound insulation on and off now for well over a month. It is a big job. Ceilings harder than the walls. Time consuming. A bit (alot) messy. Requires us to ply the walls first (where ply is needed) and then insulate. For the stud walls that don't need ply we will work as quick as we can in the evenings once the the plasterboarders are on site (due next week) filling in behind them as they plasterboard one side. Going to be a busy week. But progress is satisfying and physically working on our build again is fun.

I have previously asked about materials for loft insulation and have come down in favour of insulation roll, loft legs and standard loft board. I want to increase my loft insulation from 4” glass fibre to 10” and retain access and storage using wickes 7” loft legs and standard loft boards. Problem is according to all sources I can find, rock wool is a superior materila to glass fibre and while I would like to use it, I can't find it in 6” thickness, only 4 or 8, (100mm and 100mm) There is something called rockwool rollbatt at Jewsons https://www.jewson.co.uk/building-materials/thermal-insulation/rock-insulation/products/RWRB1503/rockwool-rollbatt-365m-x-400mm-x-150mm-pk-of-3/ Could I use Rockwool “rollbatt “ as if ti was standard roll to insulate across the joists in my loft, and board over it using loft legs? Is rock wool available anywhere in 150mm or am I misinformed about the superiority of rockwool? Finally a gripe: It is stated on US websites that rockwool has a better u value, repels moisture where glass fibre soaks it up, and is more fire resistant. It seems little has changed since I insulated my last house in 1979. There are the same two basic materials, glass wool and rock wool. Glass wool, confusingly also called glass mineral wool for some reason, confirmed by all sources as inferior to rock wool, is nonetheless almost universally available by all manufacturers, but rock wool is only made by one firm. Even products like Knauf Earthwool, which sound as though they would be more natural, and actually do feel more natural, are made of the same old glass “mineral” wool

There are quite a few rolls of rockwool insulation up in the loft that were unused. Wondered what I should do with them really. I guess the options are a. use them somewhere but where? b.leave them there as they are not in the way after all (I have never actually been in the loft!) or c. get them down and get rid of them. Views?

Having moaned about the lack of protection of my xtratherm during the house build, I now find that the garage build insulated with 100mm rockwool is randomly unprotected, protected with sacking, protected with DPC. So it has got wet in the recent horrible weather. Person A tells me it will dry out Person B tells me it never dries out Given this is an unheated garage of 70m2 I can't see how the insulation in the wall can dry out. Questions: Whats the normal accepted practice (and ideally what is best practice) for looking after the rockwool type insulation during a build? Will it really dry out? Thanks

Wickes seem to have 4 for 3 on most rock wool insulation - 100mm, 170mm, 200mm, and 200mm wrapped - until nearly Christmas. Also recently on 50mm celotex. A Trade Account and a relevant cash back Amex or Credit card might bring that up to nearly 40% off. There is also about 3% via QuidCo etc, but I can't work out how to combine that with the Trade Discount. Any ideas?