Practical experience of ceiling acoustic performance sought

[bob the builder 2]

hi

 

Posi joist

 

thanks 

[SimonD]

Just though I'd revive this thread with a link to the current Gyproc white book for floors: https://www.british-gypsum.com/specification/white-book-specification-selector/floors?system[0]=6771&f[0]=system_panel_search_content_block_system_list_view%3A6771

 

I'm currently looking to sort the impact side.

 

I've currently got a floating ply floor(which will have floor coverings in parts and bare in others) with cork underlay, osb, 175mm solid joists, 50mm counter battens for services, then 25mm wood wool boards. Still deciding on which insulation to use between the joists but on testing 100mm & 75mm Sheepswool, airbourne with either of those seems fine but the impact needs some attention. I will be adding resilient bars and was then thinking I could overboard the wood woolboards with a layer of standard PB and skim.

 

Any thoughts, critiques of this thinking?

[Iceverge]

You need to deal with 

 

1. Airpaths - lots of acoustic mastic at any joints and at the walls. Seal all gaps. 

 

2. Reverberation - A layer of fluffy stuff just to stop the drum effect.Thats why  175mm won't make much difference Vs 100mm here. 

 

3. Impact noises - decouple the surfaces. You've done this with the resilient bars and to some extent the cork. 

 

4. Add Mass. Plasterboard, standard or soundbloc or OSB is the cheapest way, more the merrier. (Insulation is a dear way to add mass)

 

 

 

 

 

[Moonshine]

7 hours ago, Iceverge said:

Impact noises - decouple the surfaces. You've done this with the resilient bars and to some extent the cork. 

 Agree which the process you outline, but the res bars don't do much to control impact noise. Not sure what the Cork product is?

 

@SimonD can you give any more details of your floating ply floor (do the panels interlock) what is the cork product? I dont think this will do much for reducing impact noise. Also make sure you put a resilient flanking strip round the perimeter of the room for it to be truly floating. Also I presume your are not screwing the ply down.

 

Also why wood wool boards under the joists?

 

100mm in the cavity is fine, you don't really need more there, just make sure it has a decent density (BG spec a min 12 kg/m3  though I feel 24 kg/m2 is a better min)

 

Put some res bars under the joists and a layer or two of 15mm Soundbloc. Boards staggered, and different length screws for each layer of boars, tape and joint it, with flexible mastic at the perimeter 

 

BTW these sorts of build ups are more akin to floors separating flats and internal floors don't need so.much treatment for building regs (unless you want to do this and have the money too).

 

Also any areas which are carpeted and will stay that way won't need a resilient layer as the underlay is it

Edited March 18 by Moonshine

[SimonD]

2 hours ago, Moonshine said:

@SimonD can you give any more details of your floating ply floor (do the panels interlock) what is the cork product? I dont think this will do much for reducing impact noise. Also make sure you put a resilient flanking strip round the perimeter of the room for it to be truly floating. Also I presume your are not screwing the ply down.

 

Yes, panels interlock. They are 1525 x 1525 15mm birch ply sheets - the original intended floor finish design for the upstairs of the house. These are routed with a tongue & groove and glued together. The cork underlay has a supposed 18dB  Delta Lw - it makes a difference compared to the uncovered osb subfloor, but not by a huge amount. It is fully floating.

 

2 hours ago, Moonshine said:

Also why wood wool boards under the joists?

 

I was gifted it as it was excess from another project - lets say it's enough for my whole downstairs ceilings. Given its acoustic properties I thought there's no harm in using it as all it cost me was a journey in the van to collect.

 

9 hours ago, Iceverge said:

Thats why  175mm won't make much difference Vs 100mm here. 

 

2 hours ago, Moonshine said:

100mm in the cavity is fine, you don't really need more there, just make sure it has a decent density (BG spec a min 12 kg/m3  though I feel 24 kg/m2 is a better min)

 

 

Good points. I'd been recommded 150mm by one manufacturer's tech department but was a bit dubious given how thicker doesn't necessarily mean better in walls either. I wondered whether there was a bit of overselling plus an assumption that thicker was better by the tech rep.

 

9 hours ago, Iceverge said:

4. Add Mass. Plasterboard, standard or soundbloc or OSB is the cheapest way, more the merrier. (Insulation is a dear way to add mass)

 

2 hours ago, Moonshine said:

Put some res bars under the joists and a layer or two of 15mm Soundbloc. Boards staggered, and different length screws for each layer of boars, tape and joint it, with flexible mastic at the perimeter 

 

That's the key here that I'm missing is to add mass.

 

2 hours ago, Moonshine said:

flexible mastic at the perimeter 

 

 

9 hours ago, Iceverge said:

Airpaths - lots of acoustic mastic at any joints and at the walls. Seal all gaps.

 

That's going to be another one of those painful jobs just like airtightness where everyone wonders where I've disappeared to for so long and they can't see anything done!

[saveasteading]

The best performing acoustic floor i did ( school classrooms) was based on it completely floating  on dense mineral wool. That spreads impact over a large area. 

Ply on joists. Layer of plasterboard for density (you might ask bm for seconds or find some offcuts.). Layer of the right mineral wool. T and G chipboard. 

Underneath, resilient bar and pb.

A noise specialist later told me that all the lab test figures are unrealistic and to always go the the next spec up.

 

[Iceverge]

37 minutes ago, SimonD said:

as gifted it as it was excess from another project - lets say it's enough for my whole downstairs ceilings. Given its acoustic properties I thought there's no harm in using it as all it cost me was a journey in the van to collect.

 

 

Have you this fitted yet? 

 

If you were to put it exposed on the ground floor ceiling it would really help quieten the echo in those rooms. 

 

The way I think about airborne noise is to compare it to water sprayed from a hose. 

 

Obviously if you were to get lots of splashback like you would from plain plasterboard then the same will happen with noise. Spray a hose onto wood wool and it'll kinda fizzle out. For sound it'll make the room much less "echo"y. 

 

 

The water hose though idea works for air gaps and reverberation too.

[Moonshine]

49 minutes ago, saveasteading said:

The best performing acoustic floor i did ( school classrooms) was based on it completely floating  on dense mineral wool. That spreads impact over a large area. 

Ply on joists. Layer of plasterboard for density (you might ask bm for seconds or find some offcuts.). Layer of the right mineral wool. T and G chipboard. 

Underneath, resilient bar and pb.

A noise specialist later told me that all the lab test figures are unrealistic and to always go the the next spec up.

 

 

I would be interested to know what system completely floats on dense mineral wool as it would surprise me that it would have the structural support. Could it have been a floor with a resilient battens (https://www.cmsdanskin.co.uk/general-construction/acoustic-floors/acoustic-resilient-battens/), with mineral wool in between the battens?

 

lab tests are different parameters that in situ testing, the R_w is a lab test and the D_nTw is an insitu measurement, the lab won't have degradation in performance due to workmanship and flanking noise. The difference between the two parameters varies dependent on those factors and if its a heavy weight (masonry / concrete) or if its lightweight (timber / steel) the difference can be up to 8 dB.

[Moonshine]

1 hour ago, SimonD said:

The cork underlay has a supposed 18dB  Delta Lw.

 

 

I was gifted it as it was excess from another project - lets say it's enough for my whole downstairs ceilings. Given its acoustic properties I thought there's no harm in using it as all it cost me was a journey in the van to collect.

 

 

That cork is pretty decent and would be enough to meet the regs for impact noise if it was a flat below

 

If you have space for it the it likely won't harm the construction and ad a bit of mass and absorption to it the construction.

[saveasteading]

1 hour ago, Iceverge said:

compare it to water sprayed from a hose. 

I'll have a think about that. 

[SimonD]

22 hours ago, Iceverge said:

Have you this fitted yet? 

 

Not fitted yet, only the test area. But my wife isn't massively into the look of it as a finish, unfortunately. I was looking forward to just spray painting it.

[Iceverge]

That's a shame. I was interested to see how much of a difference they would make to the sound. 

[SimonD]

1 hour ago, Iceverge said:

That's a shame. I was interested to see how much of a difference they would make to the sound. 

 

Me too. It's already very noticeable in the test areaand would make a really nicely muffled acoustics in every room. Maybe I'll be able to convince her when I test spray it in one of the rooms so she can see what it looks like.