Thermal vs acoustic insulation

[tentative3]

I have a query about thermal vs acoustic properties of insulating quilt. I am looking at it initially from an acoustic insulation property but would also like thermal insulation. Does anyone have any experience or any particular recommended products? Are they broadly the same thing marketed differently? I'd be insulating 3 storeys in a listed late Georgian/early Victorian terrace. There is a void under the front room downstairs, the middle room is unknown but there's certainly room for mice from what we can hear!

Is it overkill to lay acoustic quilt between the joists, relay original floorboards, assuming they're still there, underlay and then new flooring? Is there any point laying any type of acoustic product downstairs?

You don't want to block out to sound, you need to find where they're coming in and get rid of them then block the holes.
For insulation of heat it's worth it for warmer feet, but mice will chew pipes and cables we you can hear them or not

Yes, sorry, the mice comment was just a lighthearted aside. It's not their sound I want to reduce.

Ive nothing useful to say, but I'm utterly intrigued as to what sound you are trying to muffle. Tube trains?? Zombies??

I've only just started researching acoustic insulation but my understanding is that insulation within the floor cavity doesn't do a lot as the sound is transmitted from the floorboards to the joist. Acoustic underlay on top of your floorboards (and then carpet or engineered wood on top of the underlay) will do a lot more.

That's assuming the sound you want to reduce is impact noise eg footsteps? If it's not impact noise but eg TV noise then from what I read the key thing is to block up any air gaps as that's how thst kind of noise travels. So for example block up gaps between floorboards.

Ha Messy, meanwhile I'm intrigued that those are the first things that spring to your mind that I'd want to insulate against!

I do want to reduce impact noise, yes, thanks minipie, but also 'travelling' noise, such as conversations, TV, etc so looks like your 2 pronged approach will be needed.

The current floor needs to come up anyway so my thinking was just to throw whatever I can at it. Downstairs I'd love to try and reduce the transfer of sound from vehicles going over the cobbles 2 feet from the door, but I can't figure out whether the sound is primarily being transferred through the air or via the fabric of the building. We will be going for secondary glazing as well but as I said, if the floor is coming up anyway I figure I might as well try things that might not otherwise be worth the disruption of taking up the floors.

To answer your specific question, acoustic mineral wool insulation is denser than thermal insulation (it usually has a minimum density of 10kg/m3), and as a result is less effective thermally.

Also bear in mind that any mineral wool insulation is only about half as effective, thermally, than the PIR rigid foam insulation products like Kingspan or Celotex, for the equivalent thickness (but PIR costs a lot more, and is not at all effective for acoustic insulation).

Acoustics are complicated. Different materials are most effective at different frequencies: mineral wool insulation is most effective with high frequency sound (voices - particularly women's and children's - for example), whereas for low frequency noise (heavy traffic, bass beat on music), there's no substitute for mass.

Effective solutions usually use a combination of the two, therefore - you might fill a cavity with rockwool to knock out the higher frequencies, but then mount a couple of layers of high density acoustic plasterboard on resilient bars (which prevent the reverberation and flanking transmission mentioned by Minipie) to reduce the lower frequencies.

Ooh Sensus you sound like you know your stuff. Mind if I pick your brains?

We are doing a refurb soon and want to include (a) sound insulation on the main bedroom walls, to reduce noise coming from the room next door (TV, footsteps, slammed doors etc) and (b) sound insulation on our bedroom ceiling/dd's floor, to reduce noise from dd's room above (mainly footsteps).

Do you have any suggestions of what product or solution we should use for these?

(We are already spec'ing Kingspan for thermal insulation in the loft).

It depends what the construction of the bedroom walls is, of course (and the scale of the problem, and how much space you're willing to lose off the room).

Assuming they are stud walls, then the minimum would be to fill them with something like Knauf Earthwool Acoustic mineral wool insulation (this will reduce the transmission of higher frequency sounds).

Next step would be to use a couple of layers of Gyproc Soundbloc acoustic (high density) plasterboard, fixed with the sheets staggered. This adds mass to the wall, and reduces the transmission of lower frequency sounds.

As you've already identified yourself, that then leaves the problem of flanking transmission via the floors.

Without going into too much detail, best I can do here is point you in the direction of the Robust Details Handbook (Google it: you need to register with your email address, but can then download it free of charge). This has plenty of solutions for floor and ceiling treatments, but also take note of the details they use to isolate wall-floor junctions... one of the main ways to prevent flanking sound transmission is to introduce discontinuities, so for example the plasterboard on the walls should not directly contact the floor deck, but should be sealed and isolated from it using resilient strips.

Also download and read through Approved Document E to the Building Regulations, which similarly covers a lot of the basic principles and solutions.

As I said, it all depends what the scale of the problem is - whether you just casually want to minimise sound transmission where it is possible and easy to do so, or whether there's a serious and definite issue to be addressed - but, like airtightness on buildings, a lot of it comes down to attention to detail and workmanship if you want to go that extra mile.

Thank you! Very helpful indeed. Some of the walls are brick (terraced house party wall) and some will be new stud walls (internal walls).

I will google "resilient strip" but wondering if silicone would do this job ie finish the plasterboard just short of the floor and fill gap with silicon (or is that a bodgy solution...)

One last question - do wardrobes along a wall (full of clothes) provide additional soundproofing effect?

Thanks so much!

Silicone is better than nothing, but if you Google 'resilient flanking strips', you'll come across numerous products, usually based on compressible foam materials.

anything that adds mass or discontinuities (additional layers/surfaces) between you and a noise source will reduce sound transmission to some degree - so wardrobes will have some effect, certainly, but the trick is to get maximum sound reduction from minimum thickness. In other words: if you need wardrobes anyway, then great, they'll help a bit, but don't install them as a primary measure, just to reduce noise.

Fascinating 😎

Oh, just to add, Minipie... (the bit I missed), no, just stopping the plasterboard short of the floor is bad. It stops flanking transmission, but it just leaves a gap in your protection against airborn sound.

That's a bit like saying that a door will transmit sound by reverberation, so I'll just leave the door open!

Thank you! Foam strip sounds more sensible than silicon.

For some reason I stopped getting notifications for this and didn't realise there had been further replies. Very useful and interesting reading, thanks Sensus. It sounds like we have several options for our upper storeys, and indeed we are considering fake walls for the front room on each upper storey, initially because it seems we don't have sufficiently deep reveals for secondary glazing, so this would provide a framework for that, but it also gives us an opportunity to add some insulation.

The front room downstairs is difficult. We have a narrow old listed terrace, the front door opens directly into the room, and whatever doorways previously existed have been removed so this room runs into the middle sitting room, separated by the stair case. The middle sitting room has practically no original features left but the front room has decorative plasterwork on the ceiling which really prevents us from adding any mass to the walls, plus the space to get past the stairs is already fairly narrow. We believe the void/cellar runs underneath both rooms and seems to be our best opportunity for insulation, both thermal and acoustic. My primary concern is acoustic, we have a barking dog next door, cars rumbling over the cobbles immediately outside the door, and passing pedestrians (particularly late at night when they are well refreshed). We are pragmatic - we bought an old listed building in the very heart of the city; there will always be noise. However, what noise reduction we can put in place, we'd like to.

The plaster issue is why I'm looking primarily at the floor. Is there an equivalent to acoustic plasterboard which could go over the mineral wool insulation underneath the floor?

I will have a thorough look a the documents you linked, but they are beyond me today for self inflicted reasons!

"The plaster issue is why I'm looking primarily at the floor. Is there an equivalent to acoustic plasterboard which could go over the mineral wool insulation underneath the floor?"

Yes, absolutely; you can use a 'dry screed' as a 'floating' layer over the floorboards.

See following link as an example:

www.cellecta.co.uk/PDFs/ScreedBoard_28_on_existing_timber_subfloor_pct_solution.pdf

I fear that insulation within the floor won't do much for you, though, for the simple reason that most of the sound penetration will be through the walls and windows... relatively little will be finding its way in through the floor.

Brilliant, thank you.

I very much suspect you're right, I'm just at a loss as to what we can do in that one room (well, 2, given how the rooms connect). We will be getting some secondary glazing companies out and I know there are various solutions for shallow reveals, so hopefully one of them will come up with something, even if we can't achieve the optimum gap for secondary glazing. We sit in the middle sitting room so I have considered reinstating a door on one side of the staircase, but I think it would need to be a glazed door to avoid making that front room really dark and it won't do anything for the noise coming through from next door.

It may be that we just accept a minimal noise reduction downstairs and look at a much more substantial reduction upstairs where we have more options open to us.

That's why I was thinking tube trains and zombies OP- I couldn't imagine what would be producing noise underneath your ground floor!
Soft furnishings in the sitting rooms will help too- thick curtains, rugs etc, as the soft surfaces will stop the sound bouncing round so much (you have probably covered this already...) Develop a taste for woollen wall hangings??