Extension with flat roof 7.5 x 5 m (37.5 sqm). As soon as the extension and refurb are finished and there is any money left, a sedum green roof surface will be added (joists designed for the load), but initially just plain flat roof.

 

I've been quoted for:

- RubberBond Flex R Fleece Backed EPDM @ £3.9k

- Rapid One Liquid Rubber @ £4.7k

- Evermore SBS 20-year guaranteed @ £5.1k

 

Has anybody had experience with these materials at all? Used with green roof maybe?

Any other recommendations for a system happy to take sedum trays on top, or generally every decent roof membrane will be ok?

I built a green roof with good falls, 7.5degrees, 300cc joists 28mm marine ply,  normal felt, drainage layer geotextile, crushed chalk, poor subsoil, sedum plugs failsafe edge detail 

 

not leaked yet, the felt is so well protected it might never leak.

 

what are your falls?  Puddles are the enemy of flat roofs 

The fall is 1:40 or 1.4'

The total height allowed does not lend for much more I'm afraid, I'll take a note and make sure to check the surface for any local dips.

 

GRP it.

A fibreglass roof is bombproof  Pooling or lack of fall won’t effect the roof 

You need to be careful that you don’t have to much fall As the top Seddons won’t get enough water 

 

My research and the good people on this community explains that pooling in and of itself does not present an issue. However, personally I'd aim to avoid it.

On 22/05/2021 at 16:29, SteamyTea said:

GRP it.

 

On 22/05/2021 at 16:35, nod said:

A fibreglass roof is bombproof  Pooling or lack of fall won’t effect the roof 

You need to be careful that you don’t have to much fall As the top Seddons won’t get enough water 

 

 

we're having a couple of flat green roofs and the roofers I've spoken to have said that on timber frame GRP has been known to crack and would recommend single ply for a green roof.

 

(random hit from Google for single ply solution https://www.bauder.co.uk/roof-systems/waterproofing-systems/single-ply)

 

comments?

 

 

GRP shouldn't crack unless severely twisted - think of all the GRP boats getting pounded by waves etc.

Your roofers probably forgot to mention they had screwed through the GRP and it somehow cracked near the screw holes.

I am about to fit some GRP external stair tread covers.  They use them on railway concourse steps and stadiums where they have thousands of people walking on them.  I bet single ply and roofing felt would not be as tough.

+1 fir GRP, boats sit in puddles (and flex) ?

I think it was in reference to the timber frame moving/expanding/contracting etc but if people have first hand experience of flat green roofs being laid on top of GRP and they've not had any issues then that's a pretty good indication that it's ok to do! ?