Flanking transmision - OSB flooring under stud partition

[Hastings]

Building an internal 100mm stud wall on a first floor (metal-web joists) deck to separate two bedrooms in a timber frame build.

There will be no doors or sockets in the wall.

Floor joists at 400 centres run perpendicular to the partition wall, ie. from under one room to under the other room.

I will double plasterboard one or both sides of the partition, artight seal perimeters, install 75mm sound type mineral wool.

(There are two other internal stud walls on this level but they both have doors in them so not worth as much effort in preventing sound travel.)

 

For the purposes of reducing sound transmission between rooms - should I build the partition directly onto the floor joists and split the floor boarding (OSB T&G) between the two rooms or let the floor ply run continuous under the partition?

 

 

[Dan F]

This is what we've done

- Karma Isolation Strips under paritions walls to isolate walls from metal-web joists.

- Acoustic boards in each room (25mm cement + 10mm wood-fibre), i.e. not under paritions walls.

- Perimiter strips to keep acoustic boards from touching studwork.

 

[Hastings]

3 minutes ago, Dan F said:

Karma Isolation Strips under paritions walls to isolate walls from metal-web joists.

So the wall soleplate fixed straight onto the joists with only the Karma strips between?

[nod]

We normally use a 15 mil rip of plasterboard under the track Or your case sole plate 

[Hastings]

46 minutes ago, nod said:

We normally use a 15 mil rip of plasterboard under the track Or your case sole plate 

Thanks for the reply but I don't understand what you mean.

[Dan F]

2 hours ago, Hastings said:

So the wall soleplate fixed straight onto the joists with only the Karma strips between?

 

Sorry I wasn't clear:

- Joists

- 22mm caberdeck across whole first floor.

- 8mm Karma isolation strips under internal timber studs

- 89mm timber studs.

 

Between the studs:

- Celecta Screedboard type product (cement-board on robust layer).  Isolated from studwork.

- Engineered wood flooring.  Potentially with 2mm layer below.

 

 

 

[Hastings]

Thanks Dan. Looks like a good job.

Was it specified by an architect?

 

Puzzles me as to why not make the caberdek discontinuous between rooms. It's just a saw cut and would stop some transmission - a recommended design detail in a white paper from Canada I just read.

[Dan F]

31 minutes ago, Hastings said:

Puzzles me as to why not make the caberdek discontinuous between rooms. It's just a saw cut and would stop some transmission - a recommended design detail in a white paper from Canada I just read.

 

This was all part of the timber-frame package and that's how they do it.  Not sure what the disadvantage is though, asssuming it's fixed to joists and not isolated?

[Hastings]

Probably no advantage in your case using more robust layers but I am finishing with only carpet and carpet underlay.

Seems like a no-brainer to me though - separate elements wherever possible (unless perhaps you live in a seismic zone etc).

[keith65]

if you cut the flooring you will weaken the hole floor as the t & g flooring strengthens the floor by tying all the joist together. use a sound brake under the soleplate of the partition 

Edited June 3, 2021 by keith65

[Hastings]

22 minutes ago, keith65 said:

if you cut the flooring you will weaken the hole floor as the t & g flooring strengthens the floor by tying all the joist together. use a sound brake under the soleplate of the partition 

The joists run perpendicular to this partition, so I don't see how how it would affect the tying together of the joists. And they are already tied together at their ends by the external walls and in the centre by strong-backs. The partition over the top will help tie them together over the cut.

The entire upper floor deck, 5m x 10m is already divided almost in two in the middle by the stair opening running 2/3rds of the way across and in the same direction as the joists.

Also there needs to be an expansion joint dividing up the 10m run, according to the OSB install guide.

Edited June 3, 2021 by Hastings

[Mr Punter]

With timber frame the floor deck adds to the strength of the building and the deck is fixed over the entire floor, excluding the stairwell.

 

For internal partitions you can use some isolation strips at the base.  Leave the plasterboard 5mm short of the floor.  The Screedboard suggested by @Dan F is very good but you lose some ceiling height.  You could use resilient bars on the walls.  They are fairly cheap but help decouple the plasterboard.

[Hastings]

7 minutes ago, Mr Punter said:

With timber frame the floor deck adds to the strength of the building and the deck is fixed over the entire floor, excluding the stairwell.

So how do you deal with expansion/contraction over long runs?

 

I'm replacing a 150yr-old mid-floor (inside rubble stone walls) done with no ply and no glue, so it all seems so totally overkill to me.

 

Edited June 3, 2021 by Hastings

[Mr Punter]

3 minutes ago, Hastings said:

So how do you deal with expansion/contraction over long runs?

 

They don't.  I guess the chipboard expands / contracts at a similar amount as the joists - not much.

[Hastings]

6 minutes ago, Mr Punter said:

 

They don't.  I guess the chipboard expands / contracts at a similar amount as the joists - not much.

 

I don't understand this. The joists can't shrink/expand, relative to eachother, because they are fixed in position.

 

OSB T&G4 has expansion built into the joints but they say that runs of over 7.2m should have a gap, in addition to the perimeter 10mm expansion, to avoid buckling.