Can I use this roofing membrane as my internal vapour barrier?

[Co1]

My merchant tells me I’ll be fine using this product as the internal vapour barrier on my timber framed extension. 
 

https://www.roofingsuperstore.co.uk/product/cromar-vent-3-high-performance-breather-membrane-50m-x-1m.html

 

Is he correct? I’m hoping so as I have a load of it left over from another job, but it feels a bit wrong!! 
 

Thanks

Col

 

[Redbeard]

Doesn't sound right to me, but try the manuf'r. Importantly, AFAIK, it is not a vapor control layer. It is a waterproof membrane which is capable of 'breathing' *out*.

[Temp]

Not suitable. 

 

Breathable membranes are designed to allow water vapour to escape from the structure to help avoid condensation.

 

Vapour barriers are designed to stop water vapour escaping into the structure and possibly causing condensation. 

 

Vapour barriers are normally a plastic sheet like material, not a felt/fiber like material.

 

[Temp]

If you want to use that online store they sell the right stuff....

 

https://www.roofingsuperstore.co.uk/search?keywords=Vapour+barrier

 

[Temp]

Does the timber frame company require you to use a particular product for warranty purposes?

 

[bmj1]

I have no idea if this is the right product, or not, but of all the corners that can be cut, membranes is never one of them.

 

Figure out exactly what the correct membrane needs to be, and use it.

 

I'm all for being entrepreneurial, and frugal, but this is really important to get right.

[Co1]

Thanks all. I’ve reached out to the manufacturer to see what they say, but as I mentioned, it doesn’t seem right! The help is very much appreciated. 

[Co1]

I messaged Cromar last night, and at 09:04 this morning they confirmed that it wasn’t suitable. Impressive customer service! 

[JohnMo]

12 hours ago, Co1 said:

merchant tells me I’ll be fine using this product

Shows you should always check. Cheap product, with expensive repairs required in 10 to 15 years, if you had taken his poor advice.

 

Someone is possibly getting their house built now, with roof membrane as a vapour stop membrane. And the builder will do his next that way also! Doesn't bear thinking about.