AVCL Intersection from rafter to wall

[DIY-Dafydd]

Hi all,

I've been scouring the web and this forum for answers but can't seem to find it for my situation.

 

Im about to start a barn conversion of an old stone barn with 480mm walls and will be reslating the roof. The plan is to insulate over the rafters only as 1) I hate cutting PIR and 2) my rafters are only 3" so there isn't much usable space for insulation anyway.

 

The build up is:

Natural slate

25x50 Batten

Membrane - Novia Black+

38x50 counter batten secured through with helical screws

130mm PIR  

AVCL - Im thinking Novia VC2

Rafters. Which will be my service void for cables and ducting

12.5 Wood fibre board & clay plaster.

 

 

Walls are 80mm wood fibreboard and clay plaster 

 

What I cant seem to figure out is how my AVCL goes from being on top of the rafters to below it, and does it need to continue above for the full rafter length? It would be best if it can go the full length externally to weather roof the barn from wild Welsh weather. 

 

Diolch 

[Mr Punter]

On your drawing, if the green is the VCL it should go on the warm side of the insulation on the wall.  Would it be good to sheathe the roof in OSB onto the rafters, then VCL, insulation, etc.  It may make it all lock together and the VCL would be nice and flat.

[DIY-Dafydd]

Mhmm I better speak to the supplier as my wall insulation is then being plastered so It would have to remain on that side. 

Unfortunately, my stack is already getting thick so OSB isn't an option!