My house was built in the 1960s and like many it has heavy roof tiles that are laid on battons which are fixed to the rafters. The tiles seem to be held there by gravity alone - each one has a lip that engages with the batton. Between the battons and the rafters is a sheet of bituminous cloth (it looks like).
What is the purpose of this cloth?
Is it to stop the wind which might otherwise (1) blow water up the tiles and into the roof space and (2) lift off the roof tiles? or it is to catch any water that does leak in and guide it to the gutter.
I want to cut this cloth in order to remove as small patch of tiles so I can do some ridge repairs without having to climb onto the outside of the roof.
When I repair it afterwards does it need to be watertight or simply windproof?
Thanks,
Robert