Soundproofing ventilation?

[Michaelsf90]

This is my first post on anything like this so sorry if I seem amateur. We have recently purchased a 1930's/40's semi. The party wall is double brick so it's 8 inches thick. The layout of the house is a typical semi. Stairs and bathrooms on kitchen on the outside. Bedrooms and living rooms on the inside. We can hear the neighbours on a regular basis. The brick or mortar must be of poor quality. We can even hear talking at times and basically hear everything that's said.

So doing my research I have decided to soundproof. It seems the best solution is a false wall built off the party wall. A minimim one inxh gap then a timber frame fixed to the ceiling, floor and adjoining walls with some isolation strip under the timber. Fill the stud with 50mm rwa45 insulation batts. Resilient bar then two layers of 15mm soundbloc plasterboard. All edges sealed with acoustic sealant. Also 100mm rwa45 insulation placed between the joists over the ceiling and under the floor two up to two feet from the wall to address flanking noise

Now the problem is I am quite a novice when it comes to buildings. The cavity I'm creating needs to be air tight or else the soundproofing is a waste of time. But will the cavity not need any kind of ventilation? Will the fact it's air tight cause any damp? Does it need a vapour barrier going in the new stud im creating? The party wall has no cavity it is just solid double brick wall. Any advice and help on this would be much appreciated

 

[JP_]

Don't forget the loft too... didn't have too many sound problems in my last semi, but if i went into the loft I could hear them talking next door. So that will be a route of sound too. I guess boarding out the loft would help.

 

[Michaelsf90]

For the time being I'm only bothering with the ground floor as the living room is where we spend most of our time. I have topped up the insulation in the loft it is now 300mm but it isn't acoustic insulation. It's more the damp or ventilation and if it needs a vapour barrier in the new stud that I am clueless about. I don't want to go to all this effort and create damp through the work I've done

 

[endecotp]

The cavity I'm creating needs to be air tight or else the soundproofing is a waste of time.

No, it doesn’t need to be literally airtight. Your description of the construction seems accurate and it does not include an airtight barrier.

 

[^woody^]

You need to be mindful of fire spread within cavities that you create, and install appropriate barriers where necessary. And you may need to inform the insurance company of this type of work, as it could create an insurance risk.

You don't need a vapour barrier.

And you need to deal with sound coming via any joists built into the party or flank walls wall - which is typically the main cause of sound issues from neighbouring properties.

Above all though, have a good read up on this - and not from the manufacturers. It is very difficult to stop sound coming in, but easy to stop sound getting out. You may spend £000's only to make you neighbours place quieter.

 

[JP_]

alternative ideas I had when looking into this - built-in wardrobes that cover the whole wall - cost more than soundproofing, but at least you make better use of the money spent.
And bookcases full of books, with glass doors.

 

[endecotp]

What you’re describing is likely to help reduce voices and TV; it will have less effect on footsteps, washing machine vibration, and deep bass music due to conduction through the joists, as woody says. Do you know which way the joists run?

 

[Michaelsf90]

It is airborne noise that is the problem. We do hear impact noise but to stop that is nigh on impossible. We don't want a miracle. We just want to be able to watch tv and not hear next doors conversation when it's a quiet part or when it goes onto adverts. The joists run parallel to the wall. I don't think the joists run through the wall and the first joist seems to be a good ten mm away from the wall. The joists go into the walls and seem to be supported by dado walls under the floor. We have a chimney breast in one room which is probably going to be a problem but I'm hoping doing the alcoves will help

The rockwool insulation is fire rated isn't it? And I'm guessing the soundbloc board has some kind of fire rating? The acoustic sealant is definitely fire rated. What is in the insurance risk? Thank you all for the advice

 

[Michaelsf90]

I am looking at addressing the flanking noise by insulating under the floor and above the ceiling two foot away from the wool. I have gathered all this information and research myself I was just bothered about the cavity getting damp through very little to no air movement. If any moisture gets into that cavity I was worried about condensation and damp problems. I was hoping with it not being structural it's a job that can just be done myself. I have basic diy skills. I was also thinking of using soundcoat plus on the wall first to make the plaster air tight?

 

[ivixor]

Even a single skin brick wall will stop the sound of a voice so it must be coming through by another route.

What is the subfloor made of downstairs?

 

[^woody^]

The rockwool insulation is fire rated isn't it? And I'm guessing the soundbloc board has some kind of fire rating? The acoustic sealant is definitely fire rated. What is in the insurance risk? Thank you all for the advice

It's the air cavity which is the risk, not the stuff you build it from.

ie ... heat or flame starts at one place and travels unseen via a cavity to another. That's what you need to design out. The risk, or added risk is if you introduce a potentially dangerous situation that an insurer did not know about.

 

[Michaelsf90]

I'm assuming the house was built during the war or just after so could it not be cheap materials or poor mortar? I'm going to soundcoat plaster the wall first so maybe that could make a huge difference? The floor is floorboards on joists with a decent cavity to the foundations. My intentions are to insulate two feet away from the wall and seal the floorboards with acoustic sealant.

With regards to the fire safety I need to cut away at the lathe and plaster ceiling to insulate above the wall to address the flanking noise. So I will be overboarding that and sealing it with acoustic sealant. Will that address the fire issue? My guess is none of the house is up to today's fire standards with the age of it

 

[ivixor]

The quality of the mortar is not going to make any difference to the noise transmission. I think you need to look at the more obvious routes for noise, other than the 3-brick thick wall.

I wouldn't be surprised if there's a large hole in the party wall below the floor like this: http://great-home.co.uk/cms/mydata/uploads/2014/08/Sleeper-wall-with-crawl-access.jpg

If so the noise is transmitting through the floorspace. You need to get down there somehow and have a look.

 

[Michaelsf90]

The wall is two brick thick but two brick wide. So one brick thick in length. I thought myself the wall should be of better sound quality being brick but it doesn't seem to be. I'm going under the floor in the next few days to assess. Also when I cut the ceiling to shove insulation in il check the gap between the downstairs ceiling and upstairs floor. The dado walls will have those kinds of gaps in my house but shouldn't be like that going to next door. It's worth mentioning a chimney breast has been removed on that wall so their should be a concrete base under the floor for that. I hope underneath is as clean as it is in that picture! I doubt it tho

 

[ivixor]

You will not be able to hear recognisable voices through two bricks. Not unless you can see daylight through the wall. Muffled sounds and thumps maybe, but the way you describe it sounds like something else to me.