Do I or Do I not require a VCL

[MikeGrahamT21]

Hi,

 

Wanting to try and get a firm answer on this, I've got a solution for both, however the 'requires VCL' method is more expensive.

 

I have applied 90mm of EPS external wall insulation to a block - 100mm filled cavity - block contruction building. I've ran some simulations using WUFI and another app i can't even remember the name of, and both suggested even with the worst possible humidity inside, the construction would be fine and free of condensation risk, however its always been playing on my mind that these apps just might be wrong! lol

 

So if I do need a VCL, I plan to dry line the interior with a 6mm Marmox multi board (which has integral XPS as part of the construction) and then these can be direct plastered.

If I don't need a VCL, i'll just wet plaster the walls, or dry line using normal plasterboard, though would probably do it right, and wet plaster.

 

Let me know your thoughts.

 

Mike

[A_L]

FWIW the old BS5250 (Glaser) method suggests you do need a VCL, or at least a vapour check layer.

 

you might want to play with -

 

http://www.builddesk.co.uk/software/builddesk-u/condensation-risk/

 

https://www.u-wert.net/u-wert-rechner/?&lang=en

[MikeGrahamT21]

BuildDesk, that was the one I couldn't think of. I ran it through there and it said no risk.

 

BS5250 is the one which building control accept isn't it? Maybe its worth going with the marmox just to be on the safe side, like i say aside from the financial aspect, it doesn't make much difference.

 

Just had a play with u-wurt, that seems quite extreme, even with the vapour check it reckons 55 days drying time per year, and oddly how a house is normally built is even worse!

[MikeGrahamT21]

I did this again the other day, and ensured that all of the materials had the correct Mu values for water vapour, with a 20mm internal VCL via the Marmox it came down to around 2days of condensate a year, which is absolutely fine, don't think i'll get it any lower than that without losing too much space inside.

 

EDIT: Entered correct details for the Marmox and we are now condensate free, definitely the way to go.

Edited April 16, 2018 by MikeGrahamT21