Plasterboard with insulation / vapour barrier

[mordzy]

Morning all. Ordinarily I’d make a stud wall. Fill with celotex cover with a Vapor barrier and board over. But a local builder suggested just to ‘dot dab’ pre insulated boards to the wall. My first though was that they wouldn’t stick very well. But could be mechanically fixed. That said what about the vapour barrier? I can’t seem to find any boards that categorically say they incorporate this. Is it a bad idea/dodgy builder short cut?

Cheers

 

[Bonni]

Insulated boards stick to dot and dab, insulated boards and boards with the silver vapour barrier do not stick to dot and dab. So if you want boards with a vapour barrier, stud wall it is.

 

[mrrusty]

Insulated boards stick to dot and dab, insulated boards and boards with the silver vapour barrier do not stick to dot and dab. So if you want boards with a vapour barrier, stud wall it is.

This is not necessarily true. I recently used the Siniat thermal K boards which incorporate a metallized VCL and their own installation instructions confirm D&D is an appropriate fixing method https://etexassets.azureedge.net/-/dam/how to - insulate yo/pi48560/original/0455 siniat_gen_pos_ which is what I did and it all worked out fine.

 

[Bouy]

All depends whether you are concerned about water vapour passing through the plasterboard, condensing on the cooler walls giving rise to mould growth within the plasterboard/wall interface. It may be a while until anything untoward shows itself, but in the meantime you can, like mrrusty, convince yourself that everything worked out fine

 

[Wayners]

Charliediy on youtube dot and dabbed insulated board with board adhesive on brickwork. You need to pva the boards first if memory serves following guide.
I think your better off using foam to stick. Some use polymer grab along with the foam as that acts as a grab.
The foil on the back of boards is a barrier.. All depends on walls and if they are dry and free of damp.

I still think foam is better to stick. What I use

 

[mrrusty]

All depends whether you are concerned about water vapour passing through the plasterboard, condensing on the cooler walls giving rise to mould growth within the plasterboard/wall interface. It may be a while until anything untoward shows itself, but in the meantime you can, like mrrusty, convince yourself that everything worked out fine

Which is why the installation instructions inform that this method should only be used on cavity walls. The OPs question was about sticking. I can confirm that siniat insulated boards fixed with siniat adhesive to brick, as per the manufacturers instructions stick like the proverbial, The boards have a VCL, so installed correctly moisture won't pass through. Any air bypassing the plasterboard and causing interstitial condensation will do so whether it's battened or D&D'd and is in any case a different subject.

I tend to find following manufacturers installation instructions, whatever the product, is generally more reliable than relying on opinions on forums.

 

[mordzy]

Thanks for the suggestions. It’s an old house… over 200 years so walls are solid. Previous owner dot dabbed plaster board to the cold wall with no barrier or insulations. I places the board was soggy when I took it off.

I want to do it right. My research concluded that a barrier is a must to prevent due point between the insulation and colder external wall. So I need to stop moisture getting through.

If I have to build a stud wall, then I may as well put the celotex between the stud work and cover with the barrier before boarding. If I over board that with insulated board I’m just going to reduce the overall room size. Granted not my much but still and not probably gain much in terms of increased installation.

I’ve watched Charlie and others before to mixed success. Boards fall off etc. I can’t see how pva whil form a decent bond with foil either, not long term. Just seems risky.

 

[mrrusty]

If it's a solid wall you need to create a cavity. See page 9 of the instructions I linked to.

 

[^woody^]

If it's a solid wall you need to create a cavity. See page 9 of the instructions I linked to.

He would not

 

[mrrusty]

He would not

@^woody^ . Not sure why you say that. If he were to install siniat board according to their installation instructions for solid wall installation he would:-
Installation 1. Fix a dryliner track at 600mm centres to the floor and ceiling using suitable fixings. Allow for required cavity of at least 25mm

 

[mordzy]

Yeh im not sure you need a cavity? Everything I’ve read suggests that you just need VCL.

 

[^woody^]

@^woody^ . Not sure why you say that. If he were to install siniat board according to their installation instructions for solid wall installation he would:-
Installation 1. Fix a dryliner track at 600mm centres to the floor and ceiling using suitable fixings. Allow for required cavity of at least 25mm

From your quoted guide, p9

"The dryliner method should be used when upgrading an existing solid wall or to create a cavity".

So that implies the objective is to create a cavity.

However, when lining an external wall a cavity is not required, and may not even be desirable.

 

[mrrusty]

We can agree to disagree on that - Personally I would never internally insulate a solid wall without a cavity, and IMHO really should be a ventilated cavity.

 

[^woody^]

and IMHO really should be a ventilated cavity

Ventilated = draughts, and vented to where and from where - humid air from the rooms venting up the cavity or cold air vents from external venting into the warm room? And venting and also means that it needs to be drained.

Better practice would be to have a solid structure with no cavity, not venting and no air leakage.

 

[mrrusty]

Please explain what the difference is between a timber frame house construction that will be (from internal to external):-

Plasterboard => VCL => Insulation => vapour membrane => ventilated cavity => brick skin

and the order of the layers when internally insulating solid wall which IMHO should be:-
Plasterboard => VCL => insulation => vapour membrane (or the internal face of the insulated plasterboard) => ventilated cavity => solid brick wall (brick skin).

Please explain why a timber frame construction requires a ventilated cavity and internal insulation against a solid brick wall doesn't??