Stud wall construction for sound insulation (and cost)

[dnb]

We all know that getting hold of materials are a problem for small scale builders right now, so I am forced (very much against my will) to do jobs in a somewhat crackpot order depending on what arrives on the site. I am now looking at the stud walls because my very friendly wood supplier has told me they have restocked and can deliver quickly again. The price is not terrible, but there might be a better way that stops at least a portion of my overspend.

 

I am considering using steel U sections for the stud walls, with a batten of 4x2 at the top and bottom.  My thoughts are that this will be considerably cheaper and will result in better performance for conduction of sound - the connections between the two surfaces are small, and it looks like a lot less work than unconnected staggered timber. Most of the studwork will be double plasterboarded on at least one side (fire safety requirements) so there may be a game to play with the thickness of the steelwork. If I use the 94mm it is the same size as the 4x2 CLS used in the racking walls and the house comes out with room sizes as planned. So all good. But if I use 72mm I can double plasterboard both sides of the wall for the 12.5 mm less wall thickness (the wall is still just over 100mm thick) and maybe improve sound isolation performance.  The additional cost of plasterboard is easily paid for by the savings on steel over timber, but if the reduced air gap in the wall next to the sound insulation reduces performance more than the extra board increases it then it's a waste of time and money. I'm not sure how to model this so would appreciate suggestions from anyone with "experimental evidence".

 

I can't see anything obvious in the approved docs that stop me doing this and there is nothing going inside the stud walls that won't fit into a 70mm gap. Have I missed anything?

[MortarThePoint]

Wow, I was just about to start a thread on essentially the same topic. I'm considering staggered 4x2 on 600 c/c with 6x2 top and bottom plates. Insulation woven through and likely a single sheet of 15mm Soundbloc F on each side.

 

I hadn't given metal studs due consideration.

 

10 minutes ago, dnb said:

Most of the studwork will be double plasterboarded on at least one side (fire safety requirements)

 

Is this a separating wall between dwellings? I'm just wanting to keep the noise of our kids at bay.

[MortarThePoint]

There is quite a lot online if you search for "wall STC"

[MortarThePoint]

This is what I have been planning and I think it achieves an STC of around 53. Wasn't overly sure what to do with the coupling to blockwork but 2x2 should be strong with the anchors.

 

Notice only 50mm of Mineral Wool insulation. This looks similar to some I have seen, but would welcome opinions on that.

 

 

[nod]

You will get far better and probably cheaper results using MF Chanel and framing 

[MortarThePoint]

1 hour ago, nod said:

You will get far better and probably cheaper results using MF Chanel and framing 

 

You're probably right and I'm looking to use resilient bar RB1 for the ceiling so could use it for the wall too.

 

The main downside though is that I don't think the wall ends up very practical when it comes to mounting anything on it (e.g. TV, shelves etc).

[nod]

You can add a layer of ply or patras if you know where things are going 

[MortarThePoint]

2 minutes ago, nod said:

patras

what's that?

[nod]

A Pattress is a sheet of ply fixed between the studs before Pb To allow you to fix rads and TVs etc 

[saveasteading]

If doing this to comply with regulations or for own internal benefit, then building to these approved details is fine.

However if ever you have to get the sound insulation tested, then beware.

 

I had to have  a building tested once and it all failed (just) through walls and ceilings, although built precisely to the approved details.

Fortunately the testing consultant advised that we were working to too high a standard for the purpose of the rooms, and so it was ok as built.

He also advised that the stated performances are impossible to achieve in real life, and always to use a higher spec.

Why is this? To the best of my recollection, mostly flanking sound.

In the drawing above, noise will transmit through the block wall and through the floor and ceiling. Also it is difficult to seal the new wall to the other surfaces.

In the tests they don't use real situations.

 

In another project I had a situation with noise from a communal area to a quiet one, despite a wall exceeding spec. I established by ear to wall and floor testing, that  it was through the concrete floor. Cut a saw cut through the floor close to the wall and it was fine.

I now know to put that joint in at the time of the floor construction, with the cut under the wall line.

[nod]

1 hour ago, saveasteading said:

If doing this to comply with regulations or for own internal benefit, then building to these approved details is fine.

However if ever you have to get the sound insulation tested, then beware.

 

I had to have  a building tested once and it all failed (just) through walls and ceilings, although built precisely to the approved details.

Fortunately the testing consultant advised that we were working to too high a standard for the purpose of the rooms, and so it was ok as built.

He also advised that the stated performances are impossible to achieve in real life, and always to use a higher spec.

Why is this? To the best of my recollection, mostly flanking sound.

In the drawing above, noise will transmit through the block wall and through the floor and ceiling. Also it is difficult to seal the new wall to the other surfaces.

In the tests they don't use real situations.

 

In another project I had a situation with noise from a communal area to a quiet one, despite a wall exceeding spec. I established by ear to wall and floor testing, that  it was through the concrete floor. Cut a saw cut through the floor close to the wall and it was fine.

I now know to put that joint in at the time of the floor construction, with the cut under the wall line.

Soundproofing and fire proofing is a big part of my business 

It is quite easy to soundproof and exceed building regs 

[saveasteading]

 

It is quite easy to soundproof and exceed building regs 

 

'Exceeding building reg's is not necessarily a good thing if it wastes materials and money.

I'm not saying the reg's are wrong on either sound or fire, but that the tests are not necessarily realistic.

 

Agreed, worth getting right first time when it is critical.

[MortarThePoint]

2 hours ago, nod said:

A Pattress is a sheet of ply fixed between the studs before Pb To allow you to fix rads and TVs etc 

 

That works on the side without the Resilient bar, but what about the side with the bar? Just a whole skin of Plywood or OSB3?

 

Without:

With on RB side:

[dnb]

9 hours ago, MortarThePoint said:

Is this a separating wall between dwellings? I'm just wanting to keep the noise of our kids at bay

 

Not separating dwellings. I need to implement a protected corridor through part of the house as part of a fire escape. I am told that it needs more protection than one sheet of PB. I also want to keep the kid and grandad snoring noises at bay!

 

6 hours ago, nod said:

You will get far better and probably cheaper results using MF Chanel and framing 

 

I will take that as confirmation that steel should work better than timber.