stud partition attached to an external wall - risk of damp?

[gtgt]

Hi
I've just got a new house, 1910 terrace, and as often seen the soundproofing for the party wall could be better. I can hear the neighbours talking!

So, I thought I's upgrade the soundproofing of the party wall in the bedrooms. In the alcoves either side of the fireplace, I'm thinking of putting in two stud walls (separated from the party wall by cm, so an airgap is present) 2x2 timber with rockwall inserted and plasterboard (soundboard?) on top. This is often posted as a way of upgrading the soundproofing - as chimneys are often well constructed, but the party walls are often a single brick and badly mortared - so the sound leaks through there. The house has solid brick external walls, and floorboards.

What I'm worried about is the alcove where one side is the chimney, the other the external wall. By creating a cavity (remember there stud wall is separated by a cm from the party wall) is there any risk of condensation occuring at the surface of the external wall (eventually causing damage). Or am I worrying too much about this?

What if I carefully seal it up plus use waterproof plasterboard?

The alternative would be to use gyproc tri-line instead - if this was installed correctly (i.e. properly sealed around the circumference of the board) would this be better? less risky then putting in the stud wall+ small cavity??

All help and advice gratefully received!

 

[gregers]

well i would run dpc up behind the studs,and have you thought about a vapour barrier?

 

[DevilDamo]

To prevent cold bridging, provide a DPC between the masonry and timber stud, just like you would do when fixing a timber sole plate to a concrete floor.

 

[^woody^]

There is no risk of damp or condensation

However, as you are sound proofing, you should avoid fixing the frame to the structure and it should be isolated by some rubber or fibreboard etc

 

[gtgt]

Thanks for the advice so far folks...

I'd done some research on insulating insulating external walls, so had seen this can cause problems due to water vapour condensing (interstitial condensation) on the cold (now colder due to the insulation) solid walls -

So when I construct the stud wall (which will be fixed to the floor,ceiling and side walls - deliberately creating a space to the party wall to avoid sound transmission) there will be a sliver of colder external wall exposed to the cavity... hmmmm (worry worry)

Hence my concern, although I realise that what I am doing is different to an insulation project, this is different to a fully internal stud wall. I don't want to cause future grief for myself.

Regarding the vapour barrier, would that be polythene sheet stapled to the studs just before the plasterboard goes on? Is it necessary here as I guess air could work its way into the cavity through gaps in the floorboards anyway (remember there is a cavity between the stud wall and the party wall). Should I seal the gaps up and run some mastic around the wooden frame? I plan to use acoustic sealent around the edges of the plasterboard when its done.

Cheers all!!

 

[^woody^]

You may have done too much research

The party wall will be a warmer surface than the external walls, and so will not be susceptible to condensation. Further, there will be no impermeable barriers, so there will be no interstitial condensation

You also don't need a vapour barrier as the party wall is an internal wall

All you need to worry about is sorting out the sound insulation and not damp prevention

 

[gtgt]

Cheers Woody, you might be right - I think too much, a little knowledge is a dangerous thing

The bit of external wall, is all I'm worried about - as this will be colder than anything else in winter (solid wall) - A long time ago... I'd had some pretty impressive fungus growth in student digs at cold corners of rooms and external walls behind wardrobes (it was the cold m'laud, not being a student)