We could do with some soundproofing advice, we're about to do our living room

I know this is a bit off topic for GBF but I'm also aware that there are several members around who know their stuff on sound insulation.

The wall in question is effectively a party wall, single layer of bricks, with a layer of plasterboard on (the other) side, wet plastered on our side. The other side is a stairwell leading to a front door. It is an airborne noise only issue, and more thermal insulation would also be useful. We want to lose the minimum of room space.

Option 1: I was thinking of going for 20mm celotex board, then 2 layers of plasterboard (this will help with keeping the heat in as well). I'm well aware that the celotex has no mass so minimal sound dissipation, but I was planning on the plasterboard achieving the sound insulation and the celotex the heat insulation. Total thickness 45mm, and fairly easy to install. Is this a good/bad idea? Would the celotex actually make things worse? Any other ideas that would only lose very minimal wall thickness?

Option 2 I've seen the "boutique" 1x1m dense rubber isolating panels available ~10mm thick, available from specialist sound insulation companies on the web, can stick the panels to the wall and then plasterboard to the panels, but they seem to be around £37 each, I'd need at least 10sq m so the cost soon mounts up. Does anyone know if there is anything that does that same job for less (or even where to get the best price for these panels? Would still need to add celotex to get the thermal insulation so end up with alot of layers otherwise still easy to install.

Option 3 I also know that I could go for resilient bars, but then need to screw these to wooden batterns etc so the thickness soon mounts up, we could fit celotex between the batterns but then need to cut it, the installation cost increases and we're back to thinking about dense rubber panels after all.

Option 4 Entirely free-standing plasterboard wall on studwork infilled with mineral wool: obviously does the job but would be at least 100mm by my guessing: probably not necessary for the level of airborne noise anyway.

Option 5 Just stick 2 layers of plasterboard to the current wall. Risky option favored by my builder, the risk is that if it isn't enough there's no going back and starting again with one of the above.

yours confused (and thanks in advance)

Mike

I had a quick hunt, couldn't find quietrock available in the UK. But happened by chance on something called Green Glue - which people seem to rave about, it's not cheap, but as it's just the glue between the sheets it's a very straightforward solution. And could be used for another flanking noise problem I have. Would work out at c. £4.25 per sq m if use one tube per 8x4 sheet. One wonders if silicone sealant would achieve almost the same ends though for much less.

Thanks Paul anyway!

Option 4 is cheap and fairly easy, with bog standard materials. It takes up a bit of space but you are looking at 50mm with option 1 (celotex is 25mm isn't it?), could do option 4 in 80mm so it's not that much worse.

Perhaps use fermacell for the board and warmcell for the insulation to make it a bit green :)

I cannot see the point in putting in thermal insulation on a party wall.

I would use a double layer of a high density board -- say sound deadening plasterboard 2 x 18mm?

next door will likely be at the same temperature as your house or close enough to it for there to be little heat transfer.

Having been an acoustician for 5 years specialising in building acoustics, I can safely say that options 1, 2, 3 and 5 won't really offer any real noticable improvement in the sound insulation performance of the wall.

Option 3 has potential but only if you mounted the resi bars to 50 mm deep battens fixed vertically on the party wall.

The principals of acoustics are mass and isolation. So for instance, if you were to add (bond) one layer of plasterboard onto the solid brick wall, the percentage increase in mass is tiny and you have offered no isolation between the plasterboard and existing wall.

So option 1 doesn't offer enough isolation between the wall linings and the existing wall. You may get an improvement of a few decibels, but that would only just be noticable.

Option 2 is similar to option 1. Although you have added mass to the wall, the rubber is sufficiently solid to transfer the sound energy through it with relative ease.

Option 3 has potential, but only if you get a reasonable air space going between the plasterboard and the wall. So something like 50 mm vertical battens then horizontal resi bars with 50 mm glasswool insulation between the battens would offer a reasonable improvement if two layers of acoustic board are used.

Option 4 is the best, but in reality, the overall thickness would need to about 130 mm to accomodate 75 mm studs, a 25 mm void between the studs and wall, and then two layers acoustic board. Again a bit of glasswool acoustic insulation between the studs.

option 5 as mentioned above would be a waste of time.

The only way to achieve a decent improvement is to lose some room space. The simplist option is to bond a layer of British Gypsum Triline to the wall (52 mm thick version) (other manfs are out there) to the wall. That should get you a few decibels improvement with this treatment. Option 3 above, but with battens, or the best bet is option 4.

It might be worth getting a before and after sound test. The before test will let you know how good or bad it is at the moment, and also if there are any weeknesses in the wall, i.e. poor junction detail or flanking (you need to get the tester to do a listening check for you). The post test will obviously let you know how much of an improvement you have achieved.

An improvement of 3 dB would be just noticable, and an improvement of 10 dB would be a subjective halving in loudness.

Hope that helps in some way.

Timber

Stairwells tend to be hard-surfaced, echoing places. If that's the case with you, anything that can be done to reduce or dampen sound on the stairwell side - eg carpet, wall hangings etc - would lessen the job the wall needs to do. Watch out, though, as some surfaces commonly thought to be helpful by being unreflective of sound actually increase the transmission of sound into the wall. Sounds like Timber will know more detail on this if needed.

Posted By: Miked2714
Saint - I've emailed the phonewell people but no reply yet - any idea how much it costs?

Mike its around £25/m2. Boards are 1200 x 800 x 15mm thick

Thanks to everyone for the advice, I knew you'd come up trumps!

Phonewell sounds great but is too expensive really, and sounds fiddly that the edges need to be taped etc.

Current plan is for the worst wall (to stairwell), go for isolated stud partition wall from gypframe 60mm C studs (left over from another job anyway) filled with acoustic mineral wool, then two layers of plasterboard with either green glue or Tecsound SY50 membrane sandwiched in-between. Total thickness lost around 100mm.

Two walls which are not so bad (one is really just flanking noise, difficult to judge how bad), go for resilient bars attached directly to the wall with hammer fixings, possibly with neoprene tape underneath, then two layers of plasterboard with something inbetween as above. Total thickness lost around 50mm. Possibly try to find some thin 10-20mm quilt to fit into the airgap.

Suspended ceiling (which I didn't mention above largely because I'd already made up my mind) with gypframe 90mm I studs and sandwiched plasterboard as above.

I'm struggling to decide between green glue and Tecsound though.