Vapour control layer.

gears

I was just looking at the details on the SEI site for the Home Energy Saving Scheme and I noticed they have details for installing the various systems listed and as I've been looking at getting some dry lining done I thought I'd see what they had posted. And I noticed this section below

"A vapour control barrier must be included in the insulation system. This can be achieved by using, for example, a polyethene sheet applied to the warm side of the insulation. Where the vapour control barrier is an integral part of the insulated dry-lining board, careful attention must be given to the sealing of joints."

Full text (http://www.sei.ie/Grants/Pilot_Home_Energy_Saving_Scheme/contractor/National%20-%20Guidelines.pdf)

It is good to see that they are recognising that this must be done but,
1) Why did they not say breathable membrane rather than polyethene sheet.
2) What kind of system is a vapour barrier an "integral part of the insulated dry-lining board" is it just a poly-iso board with a foil backing that you have to tape some how ?
3) How do you install a vapour barrier using a "dab" system which they give instructions on installing.
4) They say it must be included, how is this possibly going to be inforced once the wall is plastered, core the wall to check ?

Slig

1- This membrane isnt meant to be breathable, its designed to stop moisture vapour.
2- The integral vapour control layer is the foil backing on the plasterboard. It doesnt work
3- As above, its the foil backing on the plasterboard or you batten out the wall, fit your membrane and then your plasterboard
4- Like many aspects of building control in this country, there is none.

gears

Slig wrote: »

1- This membrane isnt meant to be breathable, its designed to stop moisture vapour.

Would it not be better to install a breathable membrane(Intello or whatever) instead of basically a sheet of plastic

2- The integral vapour control layer is the foil backing on the plasterboard. It doesnt work

Typical of SEI suggesting this, I didn't think it worked

3- As above, its the foil backing on the plasterboard or you batten out the wall, fit your membrane and then your plasterboard

Battening out is probably the way to go then as you can fit any kind of insulation product you like, Kingspan, Xtratherm, Hemp and get a membrane in then connect it to windows to make things more air-tight.

4- Like many aspects of building control in this country, there is none.

NAME THAT TUNE........

Slig

The air inside is warmer than the air outside and can hold more moisture which will condence as it passes through the fabric of the wall and gets cooler.

A breather membrane will stop water getting into the structure but not air.

The purpose of the vapour check is to stop warm damp inside air progressing through the wall/floor/roof and condensing interstitally.It should always be on the warm side of the insulation.

For years a foil backed plasterboard slab has been deemed sufficent but as insulation values increase the risk of mould growth also increases I dont think enough emphasis has been put on this.

What I dont understand is what the difference between a vapour control layer and an air tightness membrane is.

I think that tune was by Van-Halen, something like jump, might as well jump?:D

gears

What I dont understand is what the difference between a vapour control layer and an air tightness membrane is.

Are these two not the same thing or a case of two in one when it comes to the likes of Intello or Siga ??

I think that tune was by Van-Halen, something like jump, might as well jump?:D

Well if it's jumping on the band waggon I'd say I will be and try and take a bit of these grants

GreeBo

gears wrote: »

get a membrane in then connect it to windows to make things more air-tight.

Im right in the middle of doing this and I cant figure out how to attach the VB in the window reveals. If I tape it to the window then how do I fix the plasterboard to the reveal?
Also, it looks like Im going to have space issues, which is better, 2 sheets of plasterboard or 1 sheet of plasterboard with 10mm insulation? (I have 20mm bonded so I will have to shave half of it off, removing the foil backing)

I have the same issue around the wall vents, they are just holes in the 9 inch cavity so I again cant see how to fix the vapour barrier to this, do I need to cut out extra barrier and tape it to the inside? Seems like Im just moving the problem as I wont be able to tape to the external part of the vent.

Cheers!

muffler

gears wrote: »

NAME THAT TUNE........

Read the forum charter please. Do not put text inside a quoted post.

Slig

GreeBo wrote: »

Im right in the middle of doing this and I cant figure out how to attach the VB in the window reveals. If I tape it to the window then how do I fix the plasterboard to the reveal?
Also, it looks like Im going to have space issues, which is better, 2 sheets of plasterboard or 1 sheet of plasterboard with 10mm insulation? (I have 20mm bonded so I will have to shave half of it off, removing the foil backing)

I have the same issue around the wall vents, they are just holes in the 9 inch cavity so I again cant see how to fix the vapour barrier to this, do I need to cut out extra barrier and tape it to the inside? Seems like Im just moving the problem as I wont be able to tape to the external part of the vent.

Cheers!

Siga specialise in the different tapes for fixing the membranes. They have loads of different tapes specifically for window reveals, vents and pipework protrusions, junctions between materials and around chimneys

GreeBo

hey thanks for the reply.
I guess my problem isnt attaching the vb to the window frame, its how I attach the plasterboard once I have done this.
There are only battens on the outside corner of the reveal and the previous plasterboard was just dabbed on, but since I cant dab over a VB Im a bit stuck.
I dont have the space to add another batten so I will only have 1 side fixed if I just screw it to the batten.

I guess its hard to explain if you are not sitting here looking at it like I am

Builderfromhell

It's very difficult to get the different trades, plumber, electrician, to not cut vapour barriers when installing services. I know you can get sealed sockets etc. but the guys doing the work have to put in the extar effort to do it right.

I'm of the view that external insulation is the only way to go.

Regarding SEI, it would be good if they gave practical, easy to understand info on the whole dry lining insulation method or evry cowboy in the country will be dabbing insulated plasterboard on walls, getting paid and disappearing. Mould may then ensue for reasons given in earlier post

GreeBo

I agree!
I've been scratching my head on this one for days and I think the only thing I can do is to stop the VB at the outside of the window reveal and seal it to the batten. This will mean that the reveal itself has no VB but I cant think of anything else to do.
Ideally I guess the VB would wrap around the reveal and seal to the window frame, but as above, then I have no way of fixing the plasterboard into the reveal.

Surely Im not the only person in Ireland to have this issue?
Every google result is for the US and they seem to have different window systems that extend right into the wall, meaning they dont have a reveal.