Single skin external wall - insulation and plastering

[doggles]

Hi'a

I have an old extension which is a single skin wall - want to use the room more then just a dumping ground so i;m in the process of insulating it etc etc.

have a couple of questions though. I've put in two air bricks on opposite walls facing eachother for a bit of air flow - they are only single brick size, is this sufficent? The room will have a washing machine and fridge in it.

Also I then intend to insulate the room,

I've painted the walls and ceiling with a bitumen paint currently I was going to get some polystyrene sheets 50mm thick to insulate between battens and then put vapour shield plasterboard over this.

Would this be ok? I've read alot of forum posts about gaps meaning mould will grow and damp will appear and that a membrane that is waterproof is required.

With the polystryene sheets do they need to be glued to the wall to be in full contact or just pop them in and cover them up?

So does the bitumen act as a membrane ont he wall and the vapour shield work for the platerboard?

or can you suggest a better way?

 

[PrenticeBoyofDerry]

If you intend to use polystyrene, you must be careful with electrical cable, they can not be run touching each other, as there is a chemical reaction that causes the PVC on the cable to go brittle and fail.
Might be worth considering using a different insulation that does not contain polystyrene.
Plus cable must be de-rated when completely surrounded by insulation.
Have you thought about battening out and installing thermaline boards, these will give both insulation and a vapour check barrier. Also allowing cable to run safely in the void behind.

 

[doggles]

thanks for replying prentice,

the elec cable at the moment runs in a plastic conduit, would that still be effected by the polystyrene?

with regards to thermaline boards would the principle still be the same then apart from not having to use two diff sets of materials it would just be one that does all? ....

also do i have to leave a gap between the wall and the board?

 

[PrenticeBoyofDerry]

If the cable is run in conduit, should be okay. Providing you don't stuff it full of cables.
So polystyrene can be used, not my favorite product. I prefer celotex or kingspan buit could get awy with rockwool or thermal slabs, I know it cost more but is more effective. Then I would use duplex(foilback boards) they too incoperate a Vapour Barrier, again they will cost a little more but it is worth shopping around if it's a big job.

 

[doggles]

cheers, what kinda thickness would you recomend?,

also would these do the job of both the insulation and the vapoir barrier?

Kingspan TP10, TF70 and TW55 Thermal Boards (foil backed PIR foam boards)