spacing around base of parapet

[cs21]

I will be installing  warm roof very soon with 150mm tissue faced insulation in 2 layers with an EPDM covering in one cover, 100mm and 50mm insulation staggered joints and will be mechanically fixing them with raw plug plastic thermal caps. There will be 18mm osb 8x4 sheets ontop of 9x2 joists built into the walls for a parapet.  My question is would i get away with 12mm expansion gap all around the base of the parapet where the OSB meets the parapet wal and filled with expanding foam l or should i go with a wider width. Any internal work with T&G OSB i always install with a 12mm gap where this meets the wall, would a similar gap be ok in a warm roof.   There will be ulutrix 600 vapor barrier installed on the OSB but will it bond to the expanding foam with the primer.

[Mr Punter]

Make sure you have firrings to give a fall of at least 1:40.

 

Not much will bond to expanding foam, but as the gap is only 12mm it won't matter.  Dress the vapour barrier up the parapet a bit.

[cs21]

23 minutes ago, Mr Punter said:

Make sure you have firrings to give a fall of at least 1:40.

 

Not much will bond to expanding foam, but as the gap is only 12mm it won't matter.  Dress the vapour barrier up the parapet a bit.

 

 

YEs i will have that in mind to dress it down and even over the cavity for extra protection. My firrings i can purchase is 4.8m long and 95mm on one end tappered to 0 although they are hard got these days. I will have to make my own up either with a table saw, circular saw or even a track saw if i can get my hands on one. 

[cs21]

1:40 for a 5.m run im getting just over 5 inches. 

[Mr Punter]

9 minutes ago, cs21 said:

My firrings i can purchase is 4.8m long and 95mm

 

That gives you 1 in 50 which should be OK.