The house we've bought has an two-storey outbuilding. The access to the second storey is some steps up the outside and then a 5 x 1 meter walkway along the back, with a door half way along it. That walkway is also the ceiling for the (uninsulated) workshop underneath.
Due to various failings of whoever put it up originally, the roofing felt on this walkway has leaked, and the plywood underneath it is dangerously rotten, to the point that I've managed to put a hole through it to downstairs - not ideal.
I'm going to strip it all off, and start again. The joists, thankfully, appear to be fine.
I plan to add firring strips to create a bit of a slope so that water doesn't pool on it, and lay 18mm ply (or OSB?) on top of that, and then coat in a suitable waterproof material.
The question is, what IS that material? I frequently hear that one shouldn't walk on roofing felt - so what coating IS ok to walk on?