Interstitial condensation

[Cocat2517]

Hi
I understand adding internal wall insulation increases the risk of interstitial condensation within the walls, however I've heard that it's only really an issue if adding a lot of insulation and adding less negates the risk, is this true?

I'm planning on adding 50mm Rockwool to solid stone walled house (wall thickness from 12 to 24 inches in places), is this too low amount of insulation to worry about condensation in the walls? I'm adding a vcl to the warm side, but sealing the vcl isn't going particularly well!

I also have good mechanical extraction (fans in both bathrooms and kitchen and a DriMaster piv in loft).

Thanks.

 

[foxhole]

How’s the damp air penetrating your walls ?

 

[Cocat2517]

The warm moist air in the house would pass through plasterboard & insulation and into the wall behind wouldn't it?

 

[foxhole]

The warm moist air in the house would pass through plasterboard & insulation and into the wall behind wouldn't it?

No

 

[Cocat2517]

What's the point of vcls then?

 

[foxhole]

What's the point of vcls then?

Vcls ?

 

[Cocat2517]

Vapour control layers, like the Tyvek airguard reflective I'm using. Are they not fitted to prevent warm moist air from the building passing through the wall & condensing on and within the wall itself (behind layers of plasterboard/insulation etc)?

 

[foxhole]

They are used externally , typically to prevent moisture entering building/ roof etc but allow any moisture already present to escape .

 

[Cocat2517]

https://www.permagard.co.uk/advice/installing-vcl-vapour-control-layer



So, exterior of wall, interior of wall, internal insulation, vcl, plasterboard covering.

The question is (was) with only 50mm of Rockwool internal wall insulation will interstitial condensation even be a problem, or will enough heat still pass through to keep the wall warm enough & above dew point?

 

[foxhole]

https://www.permagard.co.uk/advice/installing-vcl-vapour-control-layer

View attachment 168870

So, exterior of wall, interior of wall, internal insulation, vcl, plasterboard covering.

The question is (was) with only 50mm of Rockwool internal wall insulation will interstitial condensation even be a problem, or will enough heat still pass through to keep the wall warm enough & above dew point?

50mm rockwool would be a waste of time as would VLC in that arrangement .No moist air will get to wall to create condensation .
Simpler just to use foil back insulated plasterboard.

 

[foxhole]

Vcls can be useful in timber framed buildings but if installed incorrectly can do more damage.
Check here for a site not selling anything .
https://www.backtoearth.co.uk/what-is-a-vapour-control-layer-vcl/