# Forum Home Renovation Cladding  Blue Board - vapour permeable membrane

## duke149

I was about to order some Blue Board to finally get my cladding project started, when I noticed in the James Hardie "HardieTex System" it says "a vapour permeable membrane must be used". 
First, what is this? I understand it prevents condensation in the wall?
Is it really a must have? I currently have some wood and some Asbestos walls which are going to be replaced. 
I am first starting with the wood panel area which has been eaten by termites. Under the wood is a metal foil, like what would be used for cooking.
Is this the vapour barrier? 
I am putting insulation in the wall. I assume the vapour barrier would go between the blue board and insulation? If so, does this mean I need to remove the existing foil, or leave it? 
Lastly, where can it be purchased from? I called Bunnings and they had no idea what I was talking about.  
Regards.

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## Bloss

The existing 'foil' is likely vapour impermeable so if you would need to replace it. It is not optional - you must use it. There are other brands, but here is some info on 'breather' and 'non-breather' wraps ('breathable' means water vapour can move through the foil and that's what Hardies are talking about): Sisalation® Wall Wrap. 
When you use any foil there needs to be an airgap between it and any other insulation - foil in contact with another surface (such as batts) will conduct heat and any insulation effect it would otherwise offer will be lost. Look in the Forum Library http://www.renovateforum.com/f220/index-90136/ scroll down to Insulation and there is an guide and and insulation handbook which explains all you need to know and has diagrams etc. 
The Hardies installation booklet also has a graphics on how to install here (Section 9 page 12) attached.

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## barney118

Which one do you use for Blueboard? I know the breathable one (fine holes in it) is used for wood cladding to allow it to breathe.

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## Bloss

> Which one do you use for Blueboard? I know the breathable one (fine holes in it) is used for wood cladding to allow it to breathe.

  Ahh - as said above - vapour permeable ie: breathable ie: with holes (although many vapour permeable membranes not have 'holes' eg: Tyvek) . . .

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