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?

Thank you

  • 1
    Not answering the question directly - thus a comment. I have various felt roofs (flat-tish), and always use a couple of one square metre plyboards when walking on them. Stand on one, move the other across. Probably a much cheaper/more cheerful way round the problem, given that I need to walk on them maybe once a year, and given the extra cost of butyl, etc.
    – Tim
    Sep 10, 2023 at 13:10
  • 2
    Roofing felt isn't designed for direct, long-term exposure to the elements. It's designed to be an additional waterproofing layer that's below the visible (asphalt, metal, slate, etc.) roofing material. It's no wonder that you've got a leaking roof. #latetotheparty
    – FreeMan
    Oct 10, 2023 at 14:25
  • Roofing materials are (almost?) never designed for regular foot traffic. From your description it sounds like this is a regular foot route to the second storey. If so, the usual solution is to install an aluminum or steel walkway above the roof.
    – Matt S
    Oct 10, 2023 at 14:27
  • In the end we went with EPDM rubber sheeting with "Castle Composites Castleflex Rubber Promenade Tiles" on top of it. The only issue I've had is that the tiles constantly "walk" to the side, so that every now and then I have to shunt them back into position. Which isn't ideal, as debris falls in the gaps until I do. I need to come up with a way to stop them moving really, and it probably needs to be something on top of the tiles, thin strips of aluminium with an L-bend, screwed to the wooden slatted wall that's to one side, and also to the rubber mats underneath, maybe.
    – Codemonkey
    Oct 11, 2023 at 10:31
  • Or maybe I could/should just glue them in place - could anyone recommend what sort of glue I should use for that?
    – Codemonkey
    Oct 11, 2023 at 11:05

3 Answers 3


I would suggest putting down a good flat-roof coating (options as recommended in the other two answers from 3+ years ago), then building the walkway above that so you're walking on a (wood, composite, or metal) deck designed to be walked on and not walking on the roofing material itself. This will prolong the life of the roofing, maximizing the lifespan of the money spent on that and minimizing the likelihood of water leaking into the interior space.

  • Agree. Something as composite decking boards would be the right thing.
    – Martin
    Oct 10, 2023 at 14:24

I'd go with a butyl rubber membrane, this stuff is a sheet material comes in rolls and is glued down.

There are also liquid treatments with a fabric part and a paint part

  • Thanks Jasen. Easy enough for a keen amateur to fit properly, would you say?
    – Codemonkey
    Mar 30, 2020 at 8:58
  • And do you mind saying why you'd choose this over a elastomeric painted coating?
    – Codemonkey
    Mar 30, 2020 at 11:13
  • getting a seal where the boards meet is very difficult
    – Jasen
    Apr 2, 2020 at 8:27

What you are after is waterproof deck coat also known as elastomeric waterproof rubber base coat. There are different brands out there, pick one and go for it.

  • Google: No results found for "elastic waterproof rubber base coat".
    – Codemonkey
    Mar 28, 2020 at 19:07
  • Not possible with Google :). Here's one at a common home improvement center. homedepot.com/p/…
    – Ack
    Mar 28, 2020 at 19:22
  • 1
    The term is elastomeric roof coatings, which returns a large number of resources.
    – fred_dot_u
    Mar 28, 2020 at 19:31
  • Thanks. And to be clear are you saying you'd paint that directly onto the ply, or would you have a felt/EPDM layer first and then this on top of that?
    – Codemonkey
    Mar 28, 2020 at 22:26
  • that's an outdoor floor paint, not roof sealant.
    – Jasen
    Mar 29, 2020 at 2:53

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