Double board or layer of OSB?

[Visti]

Our architect has recommended we double up on plasterboard to get a more solid feel, and improved acoustics.

 

I've had recommendations to instead have a layer of OSB first then a layer of board. Both for the solidity, but also for affixing things directly to the wall without concern for noggins. This I very much like!

 

Questions are:

 

1. Does that combo work well acoustically?

 

2. What thickness of OSB should be used? 9, 12, 15 or 18mm? Should it varry depending on what I plan to install into the wall.

 

3. Should it be OSB or Plywood?

 

Mind there are hundreds of m2 to cover, so minor differences in price will rack up.

[ProDave]

You still won't fit really heavy stuff to OSB bit it is certainly useful.  I used 11mm OSB behind the plasterboard in my garage for that reason and it works well.

[scottishjohn]

my 1979 kit house was built that way  studs then vapour barrier  then 12mm osb then 15mm plasterboard -- walls feel good -

-but if you used insulated plaster board ,say 38mm /50mm-- you would get very solid  feel and some more insulation 

 i did this on north side of house to improve the insulation ,as the builders were not particular on filling void with mineral wool in those days .

   it also  made the room much quieter --not that it seemed noisy before --but a marked  difference

[Alex C]

If you want to put up heavy stuff 12mm ply will be better as it holds a fixing well. I used habito plasterboard which allows you to get a fixing in and also is very dense and has good acoustic properties. I doubled this up with sound bloc plasterboard in rooms that I wanted to keep quiet and then put ply behind in the kitchen/ utility and also on the stairway so I could get a really secure fixing into it. The habito is a bugger to cut as you cant score and break it, but as a reccomendation the guy that owned the dry lining firm said he was so impressed he would use it in his own house. It also needs specialist screws and has to be fixed with an impact driver.

[Alex C]

I would also go for resilient bar and double skin on your ground floor ceilings, It makes a big differnence.

[Dreadnaught]

3 minutes ago, Alex C said:

The habito is a bugger to cut as you cant score and break it

 

Habito strikes me as a half-way house towards Fermacell with regard to fixings. But as I understand it from reading the official literature with Fermacell it is possible to use the score-and-break technique.

 

On a tangent, I wonder how the specific heat capacity of OSB or plywood compares with plasterboard or Fermacell. I recall @Jeremy Harris mentioning the benefit of the combined influence of all the plasterboard in a dwelling on the thermal time constant of the internal climate.

[Alex C]

I have used fermacell as well before. Habito is denser and takes a fixing better.

[joe90]

11 minutes ago, Alex C said:

I would also go for resilient bar and double skin on your ground floor ceilings, It makes a big differnence.

 

I second this, my only regret in our new build is single plasterboard ceilings even with acoustic insulation between I joists gives little acoustic separation between floors.

[Nickfromwales]

Don’t waste your money putting plywood / OSB everywhere !!!!

Anything significant ( noggins / timber panels for ) can be decided at the outset, and there are some very robust plasterboard ( retro-fit ) fixings our there now so the point is moot afaic.

Deffo line the kitchen with plywood, 12/15mm, and the bathrooms too, for utensil / accessory fixings both now and later down, as that IMO has value. 
Boarding 100’s of m2 for nothing is just good money after bad. 
As far as acoustics are concerned, I’d say plywood would be a worse choice than double boarding with PB. If you’re really worried about noise / sound, then just double acoustic board the plant / study wall ( both sides ) and full-fill that stud void with acoustic rated Insulaton, likewise with any other problematic locations. 

Double boarding is twice the cost, simples, so use ones own noggin and just fit a single, thicker PB once . 15mm on the ceilings and room-dividing walls will be as good as 2 layers of 12mm, if you change from regular insulation to acoustic rated at noise specific junctions, so don’t spend out where you don’t have to. Outside / exterior walls can be regular ( cheap ) white 12.5mm board, as you have the blown cellulose TF, so no need for further expense there whatsoever.
 

 

[Nickfromwales]

21 minutes ago, Alex C said:

also on the stairway so I could get a really secure fixing

Great point, forgot to mention that one.

[Nickfromwales]

18 minutes ago, Alex C said:

I would also go for resilient bar and double skin on your ground floor ceilings, It makes a big difference.

That is good, and is probably where I’d spend my money in a TF house. 

[Nickfromwales]

16 minutes ago, Dreadnaught said:

On a tangent, I wonder how the specific heat capacity of OSB or plywood compares with plasterboard or Fermacell. I recall @Jeremy Harris mentioning the benefit of the combined influence of all the plasterboard in a dwelling on the thermal time constant of the internal climate.

By the time you fill the house with ‘stuff’ you’ll struggle to quantify the difference imo. 
Comparing empty house > empty house is where it would be notable I think but in real life I doubt there’s much in it at all. 
With a heated slab, the thermal time constant is just so good it’s already above and beyond the requisite to spend out further improving it. UNLESS you’re staying there for the remainder of your days I’d spend the extra cash on something else.

[Nickfromwales]

8 minutes ago, Nickfromwales said:

That is good, and is probably where I’d spend my money in a TF house. 

Note : only if it was a 2-storey house   

[Alex C]

Our ground floor is largely open plan but with a separate snug. I knew i wanted this as a quiet escape from my kids so got mbc to build a separated twin stud on these walls that was filled with sound insulation and then double skinned both sides with sound bloc and habito and fitted a fd 60 heavy door. I am really pleased with the result, but has ended up being the room my kids watch movies and play Fornite with the surround sound turned right up and you can hardly hear it in the rest of the house.

[nod]

1 hour ago, Visti said:

Our architect has recommended we double up on plasterboard to get a more solid feel, and improved acoustics.

 

I've had recommendations to instead have a layer of OSB first then a layer of board. Both for the solidity, but also for affixing things directly to the wall without concern for noggins. This I very much like!

 

Questions are:

 

1. Does that combo work well acoustically?

 

2. What thickness of OSB should be used? 9, 12, 15 or 18mm? Should it varry depending on what I plan to install into the wall.

 

3. Should it be OSB or Plywood?

 

Mind there are hundreds of m2 to cover, so minor differences in price will rack up.

Use Abito board on your top layer 

Far better acoustics 

and better to fix to than OSB

[Moonshine]

1 hour ago, Visti said:

2. What thickness of OSB should be used? 9, 12, 15 or 18mm? Should it varry depending on what I plan to install into the wall.

 

If you are only looking to get an equivalent level of acoustic performance from the OSB, then look at getting a similar surface density from the liner board, below is a link to the surface density of many plasterboard sheets.

 

If you are using standard 12.5mm Gyproc wallboard thats 8.0 kg/m², the OSB / ply thickness should be matched to this surface density. 

 

OSB has a density of around 640 kg/m3, you will need min 13mm boards to give you a surface density of 8.3 kg/m2

 

 

[Ferdinand]

Worth noting that Rockwool sound insulation is only about £3-4 per sqm.

 

Might be better for some areas.

 

F

Edited November 14, 2019 by Ferdinand

[willbish]

8 hours ago, Nickfromwales said:

15mm on the ceilings and room-dividing walls will be as good as 2 layers of 12mm

I thought it was the joints in the PB that create acoustic weak areas? Double boarding allows you to cover the joints. Not sure where I got that info, I expect it was on BuildHub somewhere.

[Oz07]

Think it's more direct transmission ie studs. Hence why resilient bars on ceilings to decouple is so good 

[Moonshine]

2 hours ago, willbish said:

I thought it was the joints in the PB that create acoustic weak areas? Double boarding allows you to cover the joints. Not sure where I got that info, I expect it was on BuildHub somewhere.

 

15mm does not equal 2x12mm of the same density.

 

No the joints don't create significant weaknesses.

 

Resilient bars are good over direct fixing, just make sure you use the right length screws, especially if double boarding.

[redtop]

11 hours ago, Alex C said:

I have used fermacell as well before. Habito is denser and takes a fixing better.

so you would go for habito over fermacell?

[redtop]

oh, has anyone tried using fermacell and then not needing to plaster? would make up for the dif in price and save a very messy trade

[PeterW]

3 minutes ago, redtop said:

oh, has anyone tried using fermacell and then not needing to plaster? would make up for the dif in price and save a very messy trade

Yep done a big extension with it and it was really good.  Jointstik and filler take some getting used to, but once you’ve mastered using Fermacell it’s a really nice product. 
 

It is just very heavy..!!

[Visti]

On 14/11/2019 at 21:40, PeterW said:

Yep done a big extension with it and it was really good.  Jointstik and filler take some getting used to, but once you’ve mastered using Fermacell it’s a really nice product. 
 

It is just very heavy..!!

 

You DIY'd that didn't you? 

 

Thanks for the great feedback all!

 

I think I'll be more strategic with how we build up our boards, with different specs for different segments of walls. I'll sit down tonight to plan it out and do pricings for the different options. Hopefully that'll give me a good acoustic performance Vs cost model to find a sweet spot!

 

I think the most substantial change are the resilience bars which I wasn't considering before. I am very keen on those now and will be adding them in.

[Alex C]

Sheet material such as habito board gets much cheaper if you can buy it by the pallet load direct rather than being delivered by your builders merchant from their store. Resilient bar is a good call and not expensive. for our 150m2 ground floor it was about £400 in materials and 2 man days to fit it. Just make sure you use the correct length screws as fixing the plasterboard with too long screws that go into timer just defeats the whole point of it isolating from them. If you do use habito you don't need any other ply or osb behind unless it is in the kitchen. In bathroom use green plasterboard with ply behind or work out exactly where fixings will be and nog locally. Dont forget bog roll holder and bathroom cabinets.

Edited November 16, 2019 by Alex C