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


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.

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  • Google: No results found for "elastic waterproof rubber base coat". – Codemonkey Mar 28 at 19:07
  • Not possible with Google :). Here's one at a common home improvement center. homedepot.com/p/… – Ack Mar 28 at 19:22
  • The term is elastomeric roof coatings, which returns a large number of resources. – fred_dot_u Mar 28 at 19:31
  • updated my answer – Ack Mar 28 at 19:32
  • 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 at 22:26

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

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

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