Wall Build Up Question

[wcavanagh]

I am looking at wall build up for my renovation project. But getting some conflicting information. The cottage external walls are 500mm solid sandstone with no DPC. The plan is to build a timber kit inside basically.

The Spec says this.
EXISTING EXTERNAL WALL UPGRADE
(U Value to equal or better 0.18 W/m2K)
Existing lath and plaster and framing to the existing natural stone external walls to be carefully removed and made good. New 25mm thick cavity between the natural stone wall and new insulation to be formed using 25x47mm timber battens at 600mm centres. 100mm Kingspan Kooltherm K12 to be mechanically fixed to new timber battens. 1 Layer of Glidevale VC Foil Ultra (combined vapour and air barrier) fixed to wall, with all reveals/laps taped up in accordance with the manufacturer’s printed instructions.
20mm service void to be formed between new insulation and plasterboard finish for new services – no services to penetrate the new insulation. 12.5mm plasterboard (moisture resistant plasterboard to kitchen and bathroom areas) finish internally, screw fixed with all joints taped and filled.

I have also been told, this.

I would usually on suggest that you strap and line the walls with the timber kit. External face of the timber kit would be finished with a vapour barrier and form a small cavity to the existing external walls.

So my question, Do I need to install a VB between the stud work and the sandstone walls? Or so I just install the VCL inside on warm side?

 

[noseall]

Vapour barriers (VCL's) go on the warm side, usually directly behind the plasterboard and are there to control the spread of moisture from inside building into the building fabric.

Moisture control (visqueen, DPM, breather membrane) Is there to prevent external moisture from entering the building' fabric from outside. Part of the buildings' fabric can be sacrificial in terms of water saturation so the positioning of a moisture barrier needs designing accordingly.

 

[freddiemercurystwin]

What's with 'making good the lathe and plaster'? Your spec sounds a bit pants, consider building a timber partition wall with say 2x4s spanning from floor to ceiling, this avoids having to fix to wall at all which will be hell if the wall is all over the place. Insulate between the studs and board over with foil backed PB. I've a some details of this spec somewhere, I'll try and remember to dig 'em out.

 

[wcavanagh]

Many Thanks,

My plan is to fit 100mm C16 floor to ceiling, and fit 100mm insulation, I have acquired this insulation already on a super deal, unfortunately it is not foil lined, so will need to install my own barrier.