vapour barrier necessary Timber Framed extension?

[bazmdiy]

Hi All,

Please can someone can give me some reassurance about vapour barriers?

I have built timber framed extension. Wall build up is :-

Timber cladding on Battens
Breather membrane
Fermacell 12.5 building board
160mm frame with 150mm celotex in studwork
Internal wall surface - pine wainscoting with fermacell boards above.

Both kitchen and bathroom will have extractor fans taking air to the outside (not recycling).

I am about to start cladding inside wall and really don't want to use vapour barrier unless something like building regs says I must!

I would welcome any comments... many thanks

 

[jeds]

Vapour barrier is essential. I can't think of any reason to not use one?

 

[cjard]

http://www.superhomes.org.uk/resources/insulation-vapour-barrier/

what, in your wall construction, are you hoping will form an effective barrier against condensation within the wall if you don't have a vapour barrier installed?

 

[wrightwoodwork]

Yeah you definitely need. Even these modern insulted external doors have to have a vapour barrier for all it will cost

 

[bazmdiy]

Hi All,

Thanks for answers. I thought the wall build up would let me get away without an internal VPC because the wall is 'breathable' from the inside to the outside? The other reason to ask if it was necessary is that in the rush to get some heating in I have fixed some panelling behind radiators and I would have to redo all the work!

Thinking further - is it normal to only apply a VPC to external walls? And what about the ceiling?

If I can get this problem sorted I'm on my way to completion after nearly three years build.

Thanks again for input. I have tried looking on the internet but haven't found any suitable articles. They often say VPC 'as required'

 

[wrightwoodwork]

The best thing when looking on the Internet is to go on any of insulation companies websites and look for the drawings that look like what you want to do and it will name each component and show where it is to go in the make up of the wall. It is perfectly normal to apply a vapour barrier to external walls. Evan though you have a breathable membrane on the outside it would not be able to cope with the moisture on its own where by putting a vapour barrier up helps the wall to cope. When it comes to ceilings there is a bit of conflicting advice. NHBC tell you not to put a vapour barrier on the ceiling and still do where everybody else tells you to like the tyvek, scottish building regs not sure about England. But I suspect they do. I spoke to technical services at tyvek last week on the matter cause I had believed you didn't put them on a ceiling. He told me it was advantages to put on the ceiling as it stops drafts etc but was not 100% necessary and the advantages out weighed the disadvantages. He told me the reason you would get mould in the ceiling was because the boards had been fitted in the cold or frost and moisture in them and will dry out or the room was too cold and raising the temperature would also cure it

 

[jeds]

I have fixed some panelling behind radiators and I would have to redo all the work!

Presumably you've yet to finish with plasterboard. The vapour layer should be between the board and the insulation so why can you not just fit the VP over your panelling and then board over?

VP isn't required in ceilings because the loft void above the ceiling should be vented.

 

[bazmdiy]

hi wrightwoodwork,

Thanks for tip - I will try celotex site.


hi jeds

The panelling behind the radiators is tongue and groove so I can't just put vcl over it. The rest of the walls are just showing timber studwork with celotex infill so can do that. Interesting note about venting ceiling void! - the roof has 225mm rafters filled with celotex. Above rafters is Tyvek Pro breather membrane then battens and welsh slate. Ceiling is tongue and groove panelling. No venting (I guess its a 'warm roof'?). It looks like I will have to do VCL on ceiling as well...

hi wrightwoodwork,

The celotex site says I should have put VCL under rafters. Thats just doable now but a pretty nasty job . I'm hoping VCL at ceiling level will be OK.

Dupont Airguard Control seems to be popular - but what a price! I don't suppose 1000 gauge polythene is acceptable?

Thanks again for input

 

[jeds]

hi jeds

The panelling behind the radiators is tongue and groove so I can't just put vcl over it. The rest of the walls are just showing timber studwork with celotex infill so can do that. Interesting note about venting ceiling void! - the roof has 225mm rafters filled with celotex.

I see. the panelling is finish - I thought you were talking about pattress panels. And the roof is a pitched roof with no ceiling void which, as you've discovered, does need a vapour layer. (It's not a warm roof though - a warm roof is something different.) 1000g polythene sheeting is perfectly ok as a vapour layer.

 

[bazmdiy]

Hi Jeds

The roof is pitched with insulation in between rafters as per Celotex website. They say VPC should be put under rafters. Theres 50mm void above insulation. So far I believe this is a warm roof. However I dont want a vaulted ceiling and have added ceiling joists which i Intend to clad with t&G boarding. I have a decision to take whether the VPC now goes over the joists or against the rafters. So far I havn't found any examples of such a roof - but I'm still looking. I'll ring Celotex tomorrow and see whether they can help.

Thanks again for input