Well, after some investigation I discovered that EPDM can indeed be bonded directly to insulation boards, and that there are various tapered boards available for over boarding existing roofs and enabling a single-ply membrane to be bonded on or mechanically fixed.
This would address several of my problems in one solution:
- Enabling me to replace the terrible existing EPDM roof, yet allowing me to still retain this underneath the replacement for additional protection
- Negating the need for heavy 18mm OSB over boards
- Creating a 1:60 or 1:80 fall where there is currently no pitch to the roof
- Creating a warm roof
The Firestone technical support said "the Firestone EPDM membrane could be fully adhered to a PIR insulation board with coated glass tissue facers. This would initially be mechanically attached through the existing waterproofing to the structural deck, using appropriate fasteners and insulation plates.” Their video also shows it being bonded on to foil-backed PIR boards too.
There seem to be a number of other examples out there, but here are some I found:
https://www.building-innovation.co.uk/products/pir-insulation-solutions/inno-bond-inno-bond-tapered
https://www.bauder.co.uk/roof-syste...-insulation-boards/tapered-pir-for-roof-falls
https://www.jablite.co.uk/application/jablite-flat-roof-tapered-insulation/
https://gradientuk.com/applications/single-ply-membranes/
ROCKWOOL, HARDROCK, Multi-Fix (DD)
www.rockwool.co.uk
https://www.achfoam.com/Insulation/RoofInsulation/Tapered-Roof-Insulation.aspx
So anyone here have any experience of doing this, or know anyone who could do it?
And also, if I'm adding a layer of insulation
above my current roof decking, do I still need to install vents in my soffit, like with a cold roof?
Thanks