Help a newbie, what should I do with this wall?

[diyexeter]

Hi all,

Just to give some background, we live in a house which is built in to a hill, the back room is our white goods room which leads from our kitchen to the outside, the far wall is built up against the earth with a tiled roof, the back wall is the subject of my query.

The far wall of the back room had a bad water problem over a number of years due to a few slipped tiles which knackered the render. I have fixed the tiles so there is no further water issues, and have removed the damaged render, re-pointed where needed and repaired the render, so now I am left with a properly rendered wall. I am planning to batten and plasterboard the wall, then have a plasterer skim it ready for painting.

I have been advised (by a friend of friend of a diyer) to tank the render, then place a PVC cover over it under the batten, then place polystyrene batts between the battens to ensure no damp comes through.
This sounds excessive to me, is it necessary?

If you were going to plasterboard a rendered wall with earth behind it what would you do?

 

[PrenticeBoyofDerry]

Do you have a moisture/damp issue with the wall?
If not there is no harm in additional protection but not really required.
With regards to insulating the wall, I would have thought the earth on reverse of wall would be an excellent insulator.