Gaps behind skirting board and sound issues

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erlendd

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Hi there,

Hope this is the right forum. I got a builder in to install an engineered wooden floor, which involved exposing the joists and also removing the old skirting. While he was at it he put down 200mm of Rockwool sound block, to block out airbourne sound from the downstairs neighbours. Actually this worked pretty well, but they got their ceiling (plasterboard) replaced and we've been able to hear them talking ever since. It's sort of odd, but it's sporadic, we can go for days without hearing them and then suddenly we hear them quite clearly. The workmen who did their ceiling confirm that they didn't disturb the Rockwool that we had put down.

I can see gaps under all my skirting boards, varying from very small up to about 12mm, because the floor isn't perfectly level. The skirting board is quite high (victorian style - 20cm), and there isn't much behind most of the skirting because when our builder pulled the original skirting off he took much of the plasterboard with it. If you tap our skirting (MDF) it sounds rather hollow, I think due to this. I've attached a picture to make it clearer.
IMG_20170731_174154.jpg

I also know our neighbour downstairs put in a ceiling light, so they have a small hole in the ceiling where the light cable comes out (which I believe they didn't have before). I'm wondering if it's worthwhile to redo all my skirting boards to fix the sound issue? A friend suggested spraying expanding foam, but I've never used that stuff before.

Does anyone have any advice about what to do in this situation?

Thanks.
 
I'm not sure if the sound issue is just the gap below the skirting though. As there is little or no plasterboard behind the skirting perhaps sound is going through the MDF skirting?
 
Are you allowed exposed wooden flooring in your flat?
Normally the carpet adds to the noise insulation, often the lease will have a clause that prohibits wood flooring .

Who owns the gap between ceiling and floor underside?
 
in an old house, the thick lime plaster is heavy, and better at blocking sound than plasterboard, so your neighbours' new ceiling will have made the problem worse.

despite what their plasterers say, it's possible that small scraps of your rockwool (squashed into gaps round the edges of the room, especially) might have fallen out or got dislodged. Gaps sometimes display themselves by dust blowing through and leaving dirty patches on the floor or carpet.

If you can get your skirting off, you might find a crack that you can re-stuff. I presume you can't easily get the floor up now.

Expanding foam is very light, so not very good for muffling sound.
 
It's shared freehold and wooden floors are permitted.

The original ceiling downstairs was plasterboard. They replaced it with a single layer of normal plasterboard 12.5mm and a second layer of blue-board, which is for sound dampening (15mm).
 
JohnD said:
i
despite what their plasterers say, it's possible that small scraps of your rockwool (squashed into gaps round the edges of the room, especially) might have fallen out or got dislodged. Gaps sometimes display themselves by dust blowing through and leaving dirty patches on the floor or carpet.

If you can get your skirting off, you might find a crack that you can re-stuff. I presume you can't easily get the floor up now.
Click to expand...
This is actually by fear - that they've disturbed the existing rockwool.

The builder who did the work told me that they were careful with the rockwool, but that they pushed it up against my floor when they installed the ceiling. I can currently use the stiff wire from a coat hanger to poke at the insulation (I bend it at the right-angle, stick it under the skirting board crack and rotate - I can feel there's something soft, which is the insulation). My fear is that perhaps around the edges some insulation fell out, or a gap was created.

I'd love to remove the skirting board, but my builder screwed AND glued it on.. so I'm not sure how exactly to get it off without damaging it.
 
If the house was converted to flats you will have sound issues , plasterboard and insulation will only reduce noise to eliminate it.
 
foxhole said:
If the house was converted to flats you will have sound issues , plasterboard and insulation will only reduce noise to eliminate it.
Click to expand...
Sure, I don't care about hearing footsteps or general noise from the neighbors above us.. but I can literally hear the guy downstairs burp at night. That's airbourne (non-impact) noise, so it must be getting through a gap surely?
 
Just for others' benefit, I basically managed to fix the problem. First I got a small borehole camera and used it to see under the floor. It turned out that the old rockwool insulation I'd put down had been moved - just slightly - in places. Crucially it wasn't touching the wall in some places. Also since the flat is old it's likely the plasterboard wouldn't be a tight fit to the wall either, this effectively creates a gap between their flat and mine. I tried stuffing some more rockwool down the gaps, but it didn't do much (to my surprise). Instead I bought some expanding foam that was rated to 60dB sound reduction and sprayed a small amount of that down to seal the join between the wall and their ceiling, and the wall and my flooring. This has almost completely removed the sound problem.

foxhole said:
All noise is airborne , or you could not hear it.
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That's not actually true in general: when you hear your own voice it's mostly conducting through your jaw bone to your ear. That's why our own voice sounds so different to use. When I said the noise from the neighbours was airbourne I just mean I'm hearing them without much attenuation: so the noise isn't conducting through some material before it reaches me. This is why I suspected a gap.

JohnD said:
Expanding foam is very light, so not very good for muffling sound.
Click to expand...
But rockwool, which is supposedly effective for reducing airbourne sound, is just as light. I did some research into why foam might work (I'm a physicist) and it turns out it's because the foam is spongy (soft) it simply doesn't vibrate properly. It's a bit like when you kick a half-inflated football and it doesn't really go far.

Anyways, I hope this helps others out there. Thanks also for the suggestions - I learned a lot doing this :-)
 
erlendd said:
I did some research into why foam might work (I'm a physicist) and it turns out it's because the foam is spongy (soft) it simply doesn't vibrate properly.
Click to expand...
Loudspeakers are often stuffed with rockwool-like foam for this very reason. Its attenuation of internal reflections makes the effective volume of the box look bigger.
 
In space, no one can hear your neighbour burp (with the possible of your neighbour, via his jawbone).
 
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