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Plan on building additional walls for soundproofing

Posted: Wed May 27, 2020 1:35 pm
by RJW91
So I recently moved into a new house, get on with the neighbour just fine but you can hear noise from their side of the party wall pretty well. Light switches, talking and especially music.

A few details about the property. It’s a semi detached bungalow, I believe built in the early 70s. Cavity walls with standard facing bricks on the outer leaf and 3” thick, (I believe) medium density blocks on the inner leaf. 2” cavity filled with what appears to be some kind of soft white foam insulation.

Along the party wall, I’m quite positive there are 2 skins of the 3” block on either side of the wall plus the 2” cavity and as the wall enters the loft space, as far as I can tell the blockwork is then laid on its width (around 215mm) between both sides of the party cavity wall, so no cavity wall in the loft space.

There is a chimey breast in both properties and I’m quite positive the flue isn’t shared. Both properties have had the fireplace removed and blocked up, although in my case I fitted an air brick. As far as I’m aware the other property hasn’t had this done.

The roof is handcut and some of the timbers span across both properties, such the purlins, ridge board, bracing etc.

Concrete floors and I’m not sure of how they have been made up exactly. The only details I can share on this are that when I removed the old warm air heater unit, there was loose sand/gravel about 4” below the floor screed around this big metal box which connected all the ductwork, that had been recessed into the floor.

Anyway, my plan is to build additional walls to suppress noise coming from the other property. For this, I intend to build 3x2 CLS stud walls 4” in from the party wall. This 4” void between the party wall and the new stud wall will be filled with 4” rockwool sound insulation slab. I will fill the gaps between the studs with an additional 2” of rockwool sound insulation and then line the walls with 1/2” OSB (so I can fix anything like shelves etc straight to the wall), followed by 2 layers of 1/2” plasterboard which will be skimmed at a later date, all joints between the OSB and plasterboard staggered.

I will keep the ventilation to the chimney breast and use some kind of acoustic liner and vent.

This is how I plan on building the wall in the master bedroom and living room. The only other room which faces onto the party wall is the airing cupboard and due to size restrictions I am unable to replicate the same structure in there. What I can manage, is a 2x2 wall fitted tight against the party wall, filled with 2” of insulation and then lined with 1/2” OSB and 1/2” plasterboard. There is a hot water cylinder in front of the wall there, taking up about half the height of that cupboard.

So, that’s the current plan, I feel it’s quite substantial and although I could make it smaller, I feel as though if I’m going to do this I would be better off going the extra mile, rather than trying to just save a couple of inches.

Obviously my concern is, how effective is this really likely to be? I would be devastated to go to all that effort for nothing.

Weak spots that I’m somewhat concerned about are where the roof timbers span between the two properties are are likely to carry vibrations along them, particularly with the bracings fitted directly to the ceiling joists. However, it might be worth pointing out that these are not all one massive length but are butted and nailed together at different points, some of which appear to be quite close to the party wall.

There are some gaps in the party wall in the loft space, particularly where these roof timbers pass through the wall and by the eaves. I don’t think it would be that difficult to fill these up with some acoustic foam.

My property had double glazing fitted. I don’t believe they were sealed around with any kind of expanding foam though and where much of the plaster is cracking and ready to fall out around the edges of the reveals I plan on filling these up with an expanding acoustic foam.

I also wonder just how much noise could enter through the vent in the chimney breast?

Might as well also mention that currently, there is no insulation in my loft at all, as I’ve still got some work to be done up there and the old stuff had been very poorly fitted. When I have nothing else to do up there, the plan is to lay 12” of rockwool across the entire loft.

If you’ve taken the time to read through all of that and consider my circumstances, let me offer you a BIG thank you! I would highly appreciate any advice or thoughts anybody can give me on this situation.

I am prepared to take a few chances regarding the effectiveness of this all, although in any case I would much rather not waste my time, money and space.

So yeah, please share your thoughts with and thanks again for giving your time, I really appreciate it.

Re: Plan on building additional walls for soundproofing

Posted: Wed May 27, 2020 11:12 pm
by stoneyboy
Hi rjw91
That is a classic issue with party wall but one hell of a solution. I cannot advise as to whether this will cure the problem but you will need to consider how you will fix the top plate of the stud wall and how you will acoustically isolate it.
Rnegards S