What is single ply on a flat roof?

[Dave D]

Hello, I've had a quote for an epdm roof. It states 18mm ply then visqueen then celotex then SINGLE PLY then the rubber.
What is single ply?
Is it the thinnest plywood they sell, if so how thick. Or a different product?

 

[Alastairreid]

Single ply normally relates to the roof covering, eg epdm.

 

[Notch7]

The full term is "single ply membrane"

I guess it means a waterproof membrane in a single sheet.

 

[Dave D]

Thanks I might have misread it.
I think I have heard of putting another sheet of ply on top so you could walk on it if you really need to?

 

[freddiemercurystwin]

He's probably either specifying a rigid insulation with a thin sheet of plywood already bonded to it eg https://www.insulationsuperstore.co...120mm-insulation-6mm-ply-2400mm-x-1200mm.html the roof membrane is then adhered to the plywood.

or some rigid insulation with separate plywood fixed above it so that the roofing membrane can then be bonded to the plywood.