Noise problems through party wall, but in one direction

[frusc]

I've been refurbing one of two semi's (the other was done by someone else). Some of you may have seen my thread about cracked plaster on one wall, and unfortunately that same wall is presenting me with another issue

There is excessive high frequency (TV, voices, alarm keypad) sound passing from the neighours. It is so bad that even the interior stud walls seem to pass less sound then the party wall.

The odd thing is that the neighbours don't appear to have the same issue, or atleast not to the same extent. I've been in there a couple of times for other reasons and haven't heard sound from my house (TV was left on for example).

Having seen both buildings stripped back, the following appear to be the same:

- Breeze Block Party wall
- Bricks between floors where joists enter wall
- 1m basement below both properties
- Joists above and below floor in question run to party wall

The differences I can see are:

- We have removed chimneys and covered with cement.
- We have 6mm fiberboard underlay and 9mm laminate, they have solid wood and carpet on floor above.
- There was a wooden wall which both sides have removed to create through lounge, we have placed a beam (running to party wall) here at advice of structural engineer, I'm not sure if other side has done so.
- We have rendered wall with hardwall (to level with cemented chimneys etc) then a layer of plasterboard (dot and dab and screwed straight onto hardwall). (If you've read my other thread you will know why we eventually went this route). They have 2x2 (or 2x4) frame then plasterboard. Given the other issues the new neighbours have with the work of the builder, I would doubt he did any other work to wall.

I've probably missed something, so will update when it comes to me.

Having read other threads I have identified/eliminated the following:

1) One of the chimney stacks has an electric fire on their side, which has a big fake flume type hole in it. I've asked them to seal the chimney above this, as that is undoubtedly allowing sound into the cavity behind.
2) The sound ingress is not restricted to chimney areas, infact they have placed their TV between the two chimney breasts and the sound levels are higher here.
3) My TV and speakers are on the opposite wall, which may be why they can't hear us as much, when they first moved in she did say they could hear us, but her husband said not.
4) I can't hear any sound coming through windows, therefore it is not flanking from this direction.
5) I can't hear any sound coming from floor, therefore I don't believe it is flanking from this direction.
6) I can hear some noise in the floor above (the ceiling of the room in question), therefore it could be flanking where the joists enter the wall.
7) When next door advising the neighbours on an issue they had on the thrid floor, I turned the speakers on in my bathroom (on other side of wall, and can control speakers over wi-fi), I could hear them through the wall. Therefore there is an issue on this floor in their direction. Again there is an old chimney on the same breast on this floor, so I suspect that is contributing.

My original conclusion was that it was due to the electric chimney on the ground floor. However, now they have placed the TV between the breasts, it is clear that is definately not the only issue. My current suspicion/hope is that it is flanking via the joist holes and then travelling down the small cavity I have between the plasterboard and hardwall. I will have to remove the skirting to lift the laminate, but atleast this is solvable.

However, the fact they can't hear as much as us is really confusing me. It leads me to believe there are bigger holes on their side funneling the sound through to smaller holes on our side. And therefore in the reverse direction not as much sound is getting through. Given how much we can hear, I should have definately have heard something through the wall when I've visited.

Sorry for the long winded post, just wanted to convey as much information as possible. Any advice and pointers will be greatly appreciated. Just hoping I don't have to redo this damn wall again

 

[frusc]

Nobody

 

[Deluks]

Well your topic doesn't make a lot of sense, sound transmission should be the same either way, assuming we're talking about the same source and the same volume.
I can only deduce that you have noisy neighbours.
Too much info in one hit for anyone to be bothered with, keep it concise and ask a few straight simple questions and we'll take it from there.
You seem to know the problem already though, gaps that need to be sealed and flanking sound issues.

Any new work you put up should really have been seperate from the existing wall. You could try putting another layer of plasterboard up with a layer of green glue. (google it)

 

[frusc]

Well your topic doesn't make a lot of sense, sound transmission should be the same either way, assuming we're talking about the same source and the same volume.
I can only deduce that you have noisy neighbours.
Too much info in one hit for anyone to be bothered with, keep it concise and ask a few straight simple questions and we'll take it from there.
You seem to know the problem already though, gaps that need to be sealed and flanking sound issues.

Any new work you put up should really have been seperate from the existing wall. You could try putting another layer of plasterboard up with a layer of green glue. (google it)

Hi, I take your point about too much info, I'd been reading other threads where people had suggested more info was needed, but obviously went over board.

As you say I've been researching the problem since it reared its ugly head and have narrowed down the possible problems. Its just the fact there appears to be a differential between how much sound travels in either direction. So that would be my primary question, is there a plausible explanation for this or are my observations likely to be incorrect?

Secondly, since there is a generous layer of hardwall on the wall, I would expect atleast some attenuation (especially of higher frequencies). Is this a correct assumption?

Because then it really points to gaps between the floors, where I assume the builder hasn't done much work to the wall.

Thanks again for advice/pointers. As you may have guessed I'm new to this, just been reading threads and picking up knowledge from there.

P.S Just googled green glue, that looks like a promising possibility. Although that would be the 4th time this wall will have been done

 

[Deluks]

Gaps under the floor are often a culprit, and should be filled with brick/mortar.

As for their side being quieter, the only way to be sure is to use a stereo playing the same track at the same distance away and measured next door with a soundmeter.
Even so, things such as thick carpets, curtains and furnishings can absorb a lot of sound, particularly higher frequencies, so it could be the room that makes it seem louder. You've stated that they have carpet whereas you have lammy, carpeted rooms are less 'echoey'

More layers of plasterboard will help with most airbourne noise, but if you have flanking sound, which may be passing through a bracket or screws, then you can come unstuck.

'Mixing up' the construction by including plywood or mdf into the wall layers can help, theory being that you need a range of materials to block a range of frequencies.

 

[frusc]

Gaps under the floor are often a culprit, and should be filled with brick/mortar.

As for their side being quieter, the only way to be sure is to use a stereo playing the same track at the same distance away and measured next door with a soundmeter.
Even so, things such as thick carpets, curtains and furnishings can absorb a lot of sound, particularly higher frequencies, so it could be the room that makes it seem louder. You've stated that they have carpet whereas you have lammy, carpeted rooms are less 'echoey'

The ground floor has solid wood floors, its the floor above which has carpets on their side. However, they do have rugs/curtains/more furniture. So you may be correct. Whereas we prefer a more minimalistic approach which coupled with the flooring probably means the sound isn't being absorbed as quickly.

More layers of plasterboard will help with most airbourne noise, but if you have flanking sound, which may be passing through a bracket or screws, then you can come unstuck.

'Mixing up' the construction by including plywood or mdf into the wall layers can help, theory being that you need a range of materials to block a range of frequencies.

I estimate the block wall to be ~250mm (Max) thick (based on distance between outside windows and inside window to wall). Assuminng 100mm blocks I would guess the wall is two blocks thick, possibly with a small cavity in the middle. Without gaps that would surely have to be enough to block most high to mid frequencies? Going to have to pull the damn skirting off to investigate the condition of the wall between the floors I think

I'm just hoping the neighbours will take more interest now they've moved in, assuming ofcourse they can hear it aswell