Visti Posted January 17, 2020 Share Posted January 17, 2020 I'm just about to place an order and started to think about installation of our acoustic insulation between the posi joists... The Rockwool RW5 come as semi-rigid slabs - would I be doing myself over by trying to fit these between the posit joists, or are there better alternatives? Main aim is to stick to as dense a material as possible (100kg/m3) I'm less worried when it comes to the stud walls. Link to comment Share on other sites More sharing options...
Moonshine Posted January 17, 2020 Share Posted January 17, 2020 (edited) 14 minutes ago, Visti said: Main aim is to stick to as dense a material as possible (100kg/m3) That is too dense for acoustics, use a max of around 48kg/m3, though really you don't need to go that high, a decent thickness (e.g. 50mm) of 24kg/m3 is enough Edited January 17, 2020 by Moonshine 1 Link to comment Share on other sites More sharing options...
ProDave Posted January 17, 2020 Share Posted January 17, 2020 Normal acoustic insulation (the stuff off a roll in my case) with strips of any old wood to support it. doesn't need to be self supporting. Link to comment Share on other sites More sharing options...
Dan F Posted January 17, 2020 Share Posted January 17, 2020 With slabs, you'd have gaps where joists are I assume, so hard to see how effictive it would be. If noise transmission is important to you might want to think about one (or both) of the following on top of the standard insulation as shown in @ProDave picture.: 1) ScreedBoard above the joists 2) Resiliant bars (or suspended ceiling system of some sort) below the joists (we haven't built yet, but this is what we plan to do) Link to comment Share on other sites More sharing options...
Visti Posted January 17, 2020 Author Share Posted January 17, 2020 Plan is the following setup with resilient bars, double board below and a membrane and acoustic mat above. Just hard to tell what is most suitable for the mineral wool given they vary so much in density. Link to comment Share on other sites More sharing options...
ADLIan Posted January 17, 2020 Share Posted January 17, 2020 For acoustic insulation denser does not equal better - at normal, commercial densities, they all do the same job. Bldg Regs need 100mm thickness at 10kg/m3 as minimum, denser will be more expensive but acoustics will be the same (the ceiling, floor finish and effect of joists has a bigger impact). Link to comment Share on other sites More sharing options...
Moonshine Posted January 18, 2020 Share Posted January 18, 2020 13 hours ago, ADLIan said: Bldg Regs need 100mm thickness at 10kg/m3 as minimum No it doesn't, building regs min requirement for internal walls and floors is Rw 40 dB, nothing specific about what you build. Rw 40 dB can be achieved on standard timber floor with 15mm wallboard and no insulation (as attached). However if you are trying to get anything like a decent acoustic separation I would strongly suggest against this construction. C106029.pdf Link to comment Share on other sites More sharing options...
ADLIan Posted January 18, 2020 Share Posted January 18, 2020 I’m aware of that. My reply was more in connection with why use a 100kg/m3 slab when there is no need to. Assuming pricing is linked to density there are probably more cost effective solutions. Link to comment Share on other sites More sharing options...
Moonshine Posted January 18, 2020 Share Posted January 18, 2020 (edited) On 17/01/2020 at 22:29, Visti said: Plan is the following setup with resilient bars, double board below and a membrane and acoustic mat above. Just hard to tell what is most suitable for the mineral wool given they vary so much in density. What you are proposing to build there is more akin to the party floor between flats in a conversion project, and it's likely to meet ADE requirements for that (DnT,w + Ctr >=43 dB / LnT,w <= 64 dB). For internal floors of a house it will be pretty much as best as you can do without independent ceilings, and way over Rw 40 dB. A couple of key construction considerations - don't screw the resilient floor boards down to joists. - make sure the floor flanking strips are installed and only cut off once the skirting is installed. - make sure your dry liners use two lengths of screws for the resilient bars, as too long on the upper board can go through and screw in and bridge to the joist. In terms of mineral wool 50mm / 24kg/m3 would likely be fine. If you find that floor or two layers of board is too much in terms of thickness, you could use resilient joist caps (for impact isolation) and one layer of 18mm floor board, thought may have a slight derogation in airborne acoustic performance. Edited January 19, 2020 by Moonshine 1 Link to comment Share on other sites More sharing options...
Visti Posted January 18, 2020 Author Share Posted January 18, 2020 Good advice, thanks @Moonshine Link to comment Share on other sites More sharing options...
Dreadnaught Posted January 19, 2020 Share Posted January 19, 2020 Once its in @Visti, I'm looking forward to hearing your real-life impressions of the acoustic performance of such a build-up. It looks thorough. Link to comment Share on other sites More sharing options...
Visti Posted January 19, 2020 Author Share Posted January 19, 2020 It is likely to be quite OTT, but I am very keen on acoustic solutions as I wake up with the slightest sound. I am even considering a layer between the two sheets of plasterboard to reduce transmission further Link to comment Share on other sites More sharing options...
ProDave Posted January 19, 2020 Share Posted January 19, 2020 Who or what are you expecting to make noise downstairs in your house that might wake you? Link to comment Share on other sites More sharing options...
Russell griffiths Posted January 19, 2020 Share Posted January 19, 2020 5 hours ago, ProDave said: Who or what are you expecting to make noise downstairs in your house that might wake you? I have been wondering this also. Link to comment Share on other sites More sharing options...
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