Sufficient Vapour Control on IWI

[Gaf]

External wall makeup (outside to inside):

 

- Parex Monorex Render

- 100mm block

- 150mm cavity bead insulation

- 100mm block

- ~5mm Parge coat (sand cement)

- 37.5mm IWI (25mm PIR) with integrated “vapour control layer”

- Skim finish

 

IWI was being installed dot dab but they weren’t sealing the perimeters or fixings. Builder said they could pin them all with mushroom fixings instead for tight to wall sealing. I spoke with Kingspan and Siniat technical departments on this - named the boards being used as having VCL and both said no issues at all pinning the boards tight with mushroom fixings.

 

Thought came to mind about vapour control on this wall buildup with multiple mushroom fixings piercing the VCL in the plasterboard.

 

All fixings are metal - I understand these can create thermal bridges but we’re preferring over plastic for fire safety (all caps being coated to avoid rust).

 

Given the 150mm CWI, that effectively places the parge coat and IWI on the warm side, so regardless of piercings in IWI VCL, I’m hoping this isn’t a recipe for condensation and mould down the line.