Radon\plastic membrane on top of Celotex

[shabbaranks]

Hi,

Currently working on a rear extension which was previously a conservatory slab base. Scrabbling the top I discovered it had 130mm of Celotex in which is good stuff. As part of the building regs we need a radon barrier - Im pretty sure there is\was a plastic barrier put in when the cowboys out the slab in for the conservatory but in case there isn't am I ok just to place it on top of the Celotex which will then have a cement screed over the top?

As I understand it this will be formed correctly between the wall cavity also.

Thanks

 

[^woody^]

As long as the barrier is continuous across the walls too.