UK air barrier \fire stop drylining boxes

[Gediks]

Hi all, hope this is in the right place. I have just studded and insulated my lounge walls with kingspan & placed a vapour barrier over the top with plasterboard, the electrician im using has isolated the circuit and told me to pass the cables through the insulated plasterboard ready to 2nd fix. He came today to complete job cutting out with regular dryline backboxes, I told him this would not seal the vapour barrier and would let the brick walls behind become wet, through condensation forming, he offered to put silcone around cable entry and lugs, Ive told him to leave it till I find some sort of vapour proof back boxes. I then visited CEF electrical & Edmundson electrical, looking for vapour proof back boxes or even fire proof, the sales lads dont know what Im talking about. Surely there must be some sort of back box that serves this purpose. What about these new build timber homes & regulations etc. Canada, America, scandinavia all have some sort of socket vapour boxes. Can someone enlighten me, sorry no pun intended.

 

[Mike Johnson]

Schnider, Legrand, Lexman and Debflex make them Example below although I can't help on a stockist in the UK.

https://www.leroymerlin.fr/produits/electricite-domotique/interrupteur-et-prise/boite-encastrement/boite-encastrement-etanche-a-air-multicloison-1-poste-s-lexman-72049005.html

 

[Gediks]

Schnider, Legrand, Lexman and Debflex make them Example below although I can't help on a stockist in the UK.

https://www.leroymerlin.fr/produits/electricite-domotique/interrupteur-et-prise/boite-encastrement/boite-encastrement-etanche-a-air-multicloison-1-poste-s-lexman-72049005.html

Thanks Mike, looks good just cant find anything on UK websites

 

[Mike Johnson]

I can't remember, but either Leyroy Merlin or Brico Depot are part of the Kingfisher Group who own B&Q, may be worth a phone call to them?

Also try RS Components.

 

[Pretty Mouth]

I strongly suspect your concern is theoretical rather than practical.

Condensation can form where warm moist air meets a cold surface. I'm assuming the insulation immediately behind the backboxes has been removed entirely? Then the cold surface will be the face of the sockets, switches etc, so that is where the condensation should form. In practice, this is unlikely outside of humid areas such as shower rooms.

If insulation remains, then the amount of moist air that will pass through the accessory, through the backbox, and through the hole in the PIR board insulation to condense on the bricks the other side is negligible. Any moisture that does form, your average porous house brick will breathe out over time.

 

[Mike Johnson]

Thats the reason for a vapour barrier between the plasterboard and insulation, the sealed back box's is to continue the integrity of the barrier and not allow interstitial condensation to form.

This sort of problem started as soon chimneys where no longer, and hermetically sealed building became the norm, the real solution is ventilation, VMC systems are wide spread in new builds, together with heat recovery inside the plenum chamber.