Seal gaps around edge of PIR on flat roof ?

[pstunt]

Looking for advice of what, if anything, should be done around the edge of PIR on flat roof where it butts up to a brick wall with regards to air tightness etc. ?

 

The roof sits on a cavity wall and is made up of Joists,18mm WBP, with breather membrane, 150mm PIR then 12mm OSB and then externally with Sarnafil roofing membrane. Under the Joist will be 12.5mm plasterboard and finished with a lightweight plaster skim.

 

My builder has just laid the PIR and taped the joins with foil tape and now begun to lay the 12mm OSB but I am trying to understand what to do with the edges. Should they be sealed in some way or is my thinking over the top ?

 

[JohnMo]

Where have defined your airtightness layer as?  I would suspect it's not there.

 

Where does the butt joint to wall land in relation to the insulation within the wall?  You will need to bridge the gap between the wall and roof insulation with insulation between the joists (mineral wool for example).

[pstunt]

To be honest, I haven't really thought about where the air tightness layer should actually be, but thinking about it would be much lower, possibly even at the plaster level.

 

The wall you see is the outer wall with the cavity insulation sitting at right angles beneath the insulation and 18mm OSB. I will have to check how much insulation there is between the joists and top it up, as required.