Vapour Control Layer

[polkablues]

Afternoon,

I am having condensation issues with an insulated pitched ceiling with taped cellotex joints, breathable membrane etc (see my other post) In order to try and remedy this i would like to instal a VCL as a secondary vcl to the taped kingspan. the pobelm being im not sure what product to use or where to buy it from.

Can anyone with experience please point me in the right direction, i called a popular merchants who offered me breathable roofing membrane as an alternative

Thanks guys

 

[fmck]

Polythene! Available at builders merchants even B&Q. If you can seal your plasterboard so no warm air reaches the cold roof then does the same thing as a vapour barrier ( polythene sheet). If you want to go for vapour barrier remember to tape the joints and I silicone the perimeter to make air tight.

 

[Blagard]

Polythene! Available at builders merchants even B&Q. If you can seal your plasterboard so no warm air reaches the cold roof then does the same thing as a vapour barrier ( polythene sheet). If you want to go for vapour barrier remember to tape the joints and I silicone the perimeter to make air tight.

No no! Sealing plasterboard does not do the same as a vapour barrier!

You are correct that he needs is a polythene vapour barrier, just like a DPM only a lighter gauge.

http://www.wickes.co.uk/invt/153230

 

[polkablues]

Thanks guys,

I'm going to give that a go, I presume duct tape all joints and staple gun to rafters is the fixing method?

 

[Blagard]

Thanks guys,

I'm going to give that a go, I presume duct tape all joints and staple gun to rafters is the fixing method?

Yes

 

[polkablues]

thanks, I'm currently having a go at it. will update with results

 

[fmck]

Polythene! Available at builders merchants even B&Q. If you can seal your plasterboard so no warm air reaches the cold roof then does the same thing as a vapour barrier ( polythene sheet). If you want to go for vapour barrier remember to tape the joints and I silicone the perimeter to make air tight.

No no! Sealing plasterboard does not do the same as a vapour barrier!

You are correct that he needs is a polythene vapour barrier, just like a DPM only a lighter gauge.

http://www.wickes.co.uk/invt/153230[/QUOTE]

Ok you've got my attention you need to explain. I haven't done it myself but I always was in the understanding that if I made the plasterboard air tight then it would serve the same purpose as a vapour barrier.

 

[Blagard]

Ok you've got my attention you need to explain. I haven't done it myself but I always was in the understanding that if I made the plasterboard air tight then it would serve the same purpose as a vapour barrier.

I think the onus is on you to demonstrate what plasterboard sealing system is an approved vapour barrier. I am always willing to accept change.

I could patch a cold water supply with a garden hose and it wouldn't leak, but I would neither offer it as a solution or do it.

 

[fmck]

Its normal practice to dot n dab insulated plasterboard to block work the vapour barrier being sealing the plasterboard?

We did this on a large new build health centre now I think about it with 100mm insulated plasterboard. How else would you provide a vapour barrier with this size of board on block work.

 

[Blagard]

Its normal practice to dot n dab insulated plasterboard to block work the vapour barrier being sealing the plasterboard?

We did this on a large new build health centre now I think about it with 100mm insulated plasterboard. How else would you provide a vapour barrier with this size of board on block work.

Using a plasterboard with an integral vapour control layer (like Kingspan K17) is not what we are talking about You were advising sealing plasterboard with something you say you have not used

 

[fmck]

Your right I forgot that they have a vapour barrier within. possibly the foam itself as I don't remember seeing it when cutting. I still believe its possible to seal off without having to use polythene. We used eggshell paint when using the insulated board as at the end of the day it still has joints.(architect spec)
Sealed plasterboard with a suitable finish should work. Albeit I know its a pain putting the polythene on ceilings still worth doing.

 

[BigIan]

Another approach to this could be increased ventilation in the area. If you could provide more information about the area, Is it a typically moist area (Kitchen or Bathroom)

And do you mean you are having condensation issues in the roof space above the ceiling? as I`m assuming this is why you would like to introduce a VCL as if its form at inished ceiling height another VCL wond do much to cure the issue.
If so is the condensation forming above or below the insulation? I.E warm / cold roof construction?

If youe gtting condensation issues in a singe area that is normally a sign of an issue with insulation in the area as condensation only forms on cold surfaces. and as such another method to rectify this situation is to increase the levels of insulation in that area.

But no matter what approach you take I would seriously look at improving the ventilation in the area as that moist air will want to go some where.

 

[polkablues]

Another approach to this could be increased ventilation in the area. If you could provide more information about the area, Is it a typically moist area (Kitchen or Bathroom)

And do you mean you are having condensation issues in the roof space above the ceiling? as I`m assuming this is why you would like to introduce a VCL as if its form at inished ceiling height another VCL wond do much to cure the issue.
If so is the condensation forming above or below the insulation? I.E warm / cold roof construction?

If youe gtting condensation issues in a singe area that is normally a sign of an issue with insulation in the area as condensation only forms on cold surfaces. and as such another method to rectify this situation is to increase the levels of insulation in that area.

But no matter what approach you take I would seriously look at improving the ventilation in the area as that moist air will want to go some where.

Hi Ian, its a new build lean to type extension with mono pitched roof built up from, marley moderns, 25x50 batten, cromar vent3 membrane, 50mm air gap, 100mm kingspan between rafters, 50mm kingspan under rafters (aluminium taped at joints) 25mm battens then plasterboard. No vents at eaves

The extension is not currently in use but will eventually become a kitchen dinner, the underfloor heating is working and its weather tight. The condensation is forming on the underside of the roofing membrane and running down to its nearest exit, ie roof window. Between the insulation and the underside of the membrane its very wet in the air gap

Im fitting the vcl but im not 100pc that will cure it.

any other suggestions?

 

[BigIan]

Sounds like a VCL could certainly help but you still need to deal with all the moist air in the room especially, if it is to become a kitchen.
How do you intend to deal with extraction when it is in use?

Also how long has this extension been built? As there will be a masdive amount of moisture released for the first few weeks as concrete/plaster/mortar drys out which could be causing your issues short term

 

[NS215]

Has it recently been built as it could just be condesation from the building drying out, we did one a year ago on top of an existing garage and the roof space looked like it had been hosed down it was that wet, took a while to dry out, but fine now !!