Sound proofing terraced house.

[andrewpreece]

"Andy Hide" wrote in message news: [e-mail]...

You seem to have the correct ( AFAIK ) ideas to start with. Noise leaks disproportionately through small airgaps, so they are the first thing that should be eliminated. Some other suggestions, not based on practical experience I'm afraid: if you are able to get at the floor joists, presumably this is from below? If so, you could stuff insulation between the joists perhaps, as an alternative or in addition to hardboard. Maybe Cellotex, which I believe is a foam sheet material, or rockwool, but the rockwool would need to be held captive by something. Your suggestions all seem sound, though I wonder if it would be better to stuff a stiff mix of mortar around the joists where they enter the wall? Not sure, but mass is good at reflecting sound, but foam doesn't have a lot of mass, maybe it's better at absorbing sound. Finally, if you share floor joists with next door, I wonder if they transmit sound along their length? Hard to tell, but short of sawing them off at the wall and screwing them to a new wall batten somehow, another idea would be to pour dry sand into the space between the floorboards and the joists ( of course you would need some robust sheet material screwed to the underside of the joists as well, to stop it falling straight through ). The sand acts as additonal mass and, I believe, damping. These are all finger-in-the-air suggestions, I can't argue with any of what you are proposing, these are just ideas to try if you solutions don't work as well as expected,

Andy.

[Andy Hide]

My brother has just brought a c1920's terraced house. The houses along the terrace are paired and it's the dividing wall between the paired side that's causing the problem (i.e. front door next to front door).

From the non-paired side the noise is about what I would consider to be "normal" i.e. muffled sounds. If someone was shouting you would hear it but otherwise nothing more than thuds and maybe the faint sound of voices if everything was quiet.

The paired side is another story. On this side you can hear

*everything* clearly. The wall appears to be double thickness house brick. (not sure if there is a cavity or not).

On lifting a few of the floor boards it appears that the joists supporting the floor are actually joined between the houses on the problem side. There are 10mm gaps around the joists where they are passed through the brickwork.

Does anyone have any ideas on how to reduce the level of noise ?

I had the following idea of:

1) Filling the gaps around the joists under the floor with expanding foam. 2) Hardboarding over the floor to seal up any gaps between the boards 3) Gap filling under the skirting around the edges of the floor 4) Fitting a good quality carpet underlay 5) Fitting a good quality carpet.

Any ideas on whether this is likely to help the situation? I have read other posts on this forum which talk about building a stud wall but am not sure if this will help if the adjoined joists are the cause of the problem.

Thanks,

Andy.

[BigWallop]

You could also shoot the neighbours. :-)

Not knowing exactly how these houses are constructed is a problem in giving good advice on how to reduce the sounds percolating through. But the usual advice is to fill all the air gaps between the two properties. Some of these terraced builds have combined footings (foundations) and also shared loft spaces. This can cause even the slightest sounds to travel through to next door by the science of vibration along the shared timbers and the brickwork.

Placing cushion pads under any shared joists may also help to reduce the vibrations travelling along them. The dividing wall could also be lined with studio grade sound pads under a new plasterboard facing. Increasing the weight on top of any shared structures will also help to reduce the vibrations along them, but you then have to watch the bulk mass being carried on the original build.

You could start by finding all the air gaps shared between the two houses and filling them with an expanding foam. It's cheap enough to give a try and won't hurt any.

[Owain]

"BigWallop" wrote | Some of these terraced builds have combined footings (foundations) | and also shared loft spaces.

Shared loft spaces can also be a major security risk, especially if any other house in the terrace is unoccupied or squatted, and can become attractive to vermin. On the upside they may provide an escape route from fire, through the loft and across into neighbouring houses.

Owain

[Jimmy]

In your case, sealing the joist holes with styrofoam sounds like a good place to start. While you've got the carpets up you might want to try is cover your floorboards with something airtight before reinstalling the carpets. This would hopefully reduce the amout of airborne sound coming up through the gaps bewteen the floorboards.

I have a similar problem, but I don;t know how much of the sound is coming directly through the part wall. I am thinking of building a double skin of 12mm plasterboard over the party wall, separated from from it by a 3" gap, with rockwool in the gap. Comments appreciated.

J

[BigWallop]

Anything tightly packed into the gap is also going to transfer the sound through, so don't put anything in between the new skin and the party wall. You should also try to cushion the studwork away from the party to make sure it also doesn't vibrate with the sounds acting on the party wall.

[andrewpreece]

Strictly speaking, whether packing the gap wth rockwool is good or bad depends on whether more sound is transmitted by the rockwool, or whether more is soaked up by it as the sound first goes through it the first time, then reverberates in the gap between the party wall and the plasterboard. There are two ways to kill sound, reflection and absorption and I daresay it would be better to use both than just one or the other. I suspect that you could hedge your bets somewhat by using rockwool but keeping it out of contact with the plasterboard ( or party wall ). The whole subject of sound reduction is a bit difficult, and the best you can do is adopt every precaution.

The previous poster is right about the studwork needing to be decoupled from the party wall, else it acts as a short circuit for sound to cross the airgap. Quite how you go about that is another thing. I've heard talk of resilient mounts or affixing the stud work to the floor and ceiling only, or a combination of methods. Then there's the question of how you seal the plasterboard to the ceiling/walls/floor around its perimeter: leave a gap and you have a leakage path, fix the plasterboard solidly and you have a sound 'short-circuit' of sorts! Good luck,

Andy.

[Jimmy]

Thanks to you and BigWallop for the comments, Yes, I'm no expert on soundproofing, but I've notice when reading the Building Regulations about methods of soundproofing ceilings, using a second suspended ceiling attached at the walls but not touching the existing ceiling, they rocommend using rockwool or similar in the space between the old ceiling and the new one. They say it doesn't matter if the rockwool is touching both surfaces, as long as it's not packed tight - and that sounds about right to me.

Regarding doing a similar setup to sound-insulate a party wall, I am thinking of using a timber frame (probably made of 2x2, fixed to the floor, the ceiling and to the walls at each end of the room that are

90 degrees to the party wall. OK, there is bound to be a little bit of soundwave transmission through the fixing points, but due to the weight of the double skin of plasterboard, and the rockwool acting as damping, I can't envisage much of that vibration acting on the double layer of plasterboard, turning it into a giant soundboard. If the resulting soundproofing is insufficient, another layer of plasterboard can be added. In fact, come to think of it, it would make sense to start off with a single skin of 12mm plasterboad and see if that's suficient. If not, add another layer.

Going back to the question of whether or not to let the rockwool touch both surfaces, I suspect it may be better to let it touch both surfaces because it will then act as a vibration damper. I really can't imagine that the rockwool itself will conduct sound waves into the plasterboard unless it was packed very tightly indeed. As I said, I'm not an expert. These are just my impressions based on real life experience of how sound transmission behaves and from reading a few things on the subject. Comments welcome.

J

[andrewpreece]

plasterboard.

I think you are right about the rockwool not transmitting too much sound if it is loose: it has very little stiffness when loose, and its mass is very little anyway so that sounds OK. You may also be right about it damping the plasterboard a little, as the plasterboard will resonate slightly as the sound strikes it. I have located an audio book, and there is a section in it on sound reduction. The subject is complicated, with stiffness of walls dominating at low frequency, then there's a resonant region, then there's the mass-controlled region, then there's the coincincidence controlled region, none of which is any use to you, but I will reproduce a littlte of the more practical advice:-

"Cavity Walls: ...the springiness of the air between the cavities reacts with the mass of the leaves to produce resonance. The resoant frequency should be below 100 Hz which is achieved by a wide cavity ( 1m or more ) or leaves of large mass, or boh.....these resonances can be reduced by introducing an absorbent lining such as fibreglass into the cavity. It is especially useful where practical considerations limit the thickness of the wall thus raising the lower resonance above 100 Hz. The sound reduction of a cavity wall is limited by the necessary edge, tie and footing connections,as these form leakage paths to conduct sound between the leaves. Any practical cnsideration which can miimise or even eliminate these will greatly improve the sound reduction index"

"Flanking Walls: As these conduct sound into the receiving area, there is lttle point in improving the insulation of the intervening wall beyond a certan level unless the flanking walls can also be isolated structurally"

There is more info on damping, floating floors, ceilings, doors, windows,airconditioning vents etc that I could provide on request,

cheers,

Andy.

[Jimmy]

Thank you for posting that. Strangely enough, I learned a lot about sound by studying loudspeaker eclosure design technique. Your passage above touches on the subject of resonance. Where any two parallel surfaces are involved (speaker cabinet or guitar soundbox or possibly even a cavity wall) there will be a resonant frequency where a small frequency range will be amplified. I'm not sure how relevent this is to cavity walls. probably 'not very' if rockwool is loosely packed into the cavity.

J

[andrewpreece]

structurally"

Yes, I missed one sentence out of the excerpt ..."In addition there is a cavity resonance at about 250Hz which reduces sound insulation": this followed the last sentence I reproduced in the 'cavity walls' paragraph.

I'm of an electronic background, and very similar effects occur with radio signals, light or electrical waves going down cables. I would think that for sound a resonance would occur where the gap between cavities is 1/2 a wavelegth, as any sound wave of that frequency that reverberates back and forth in a cavity will build up, rather than cancel out. Probably there will be resonances at multiples of 1/2 wavelength as well, i.e. 1, 1.5, 2 etc. If your cavity is 2inches and the speed of sound in air is 335m/s then I reckon your lowest resonant frequency will be 3350 Hz! LOL, that doesn't tie in with what the book says! Going with the stuff they talked about earlier viz a 1m cavity and a resonance below 100Hz, I don't think they are talking about standard size cavity walls, or 2" studwork.

None of which is very helpful, I suspect most of the noise you want to eliminate will be below 1 or 2kHz anyway,

Andy.