Converting a GRP flat roof to green roof

[Bitpipe]

Hello, we have two small GRPd flat roofs, both of which have aesthetic issues but are otherwise sound.

 

The front one (3m x 2m) was not built with sufficient side to side falls so water tends to puddle in the middle, eventually evaporates but leaves an unsightly red stain due to algae.

 

Rear one, more or less same size, had patches of the topcoat curl up and flake off after a year or two. Roofer came back to remedy but it just happened again so no idea why.

 

I'm inspired by @Thorfun's beautiful green roofs so wondering if there is a possibility I could just lay some seedum rolls and let that cover up the issues.

 

Probably being naive here wrt weight etc but worth a thought!

[tonyshouse]

Yes, soil and water are heavy so structural calcs should be carried out, not good the puddle, small roof is more likely to pass 

 

 

[Bitpipe]

  On 02/05/2022 at 14:43, tonyshouse said:

Yes, soil and water are heavy so structural calcs should be carried out, not good the puddle, small roof is more likely to pass 

 

 

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Ok, I'll go back to MBC and see if they can review the original calcs.

[SteamyTea]

  On 02/05/2022 at 14:36, Bitpipe said:

had patches of the topcoat curl up and flake off after a year or two. Roofer came back to remedy but it just happened again so no idea why.

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3 main reasons.

Incompatible resin type mixes.

Poor preparation.

Thermal expansion and contraction.

 

My guess would be the first one.

[tonyshouse]

Usually for green roof joists are thicker and deeper and closer together the decking 28mm stronger ply too 

[PeterW]

Consider the M-Tray system @Bitpipe - they use lightweight aggregate and other methods to keep the weight down and it comes in at around 100kg/M when saturated so it isn’t a massive loading on any structure. 
 

https://jjroofingsupplies.co.uk/flat-roofing/wallbarn-m-trayr-sedum-green-roof-module-500-x-500-x-100mmp

[Thorfun]

  On 02/05/2022 at 14:36, Bitpipe said:

I'm inspired by @Thorfun's beautiful green roofs so wondering if there is a possibility I could just lay some seedum rolls and let that cover up the issues.

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😊

 

I found this when researching green roofs online https://www.turfonline.co.uk/blog/green-roof-construction/ which gives information about loadings etc. need to get the load calculated by the SE as you suggested you would do anyway.

 

our roof is single-ply membrane rather than GRP as I was told by a few roofers that GRP could crack with the movement of the timber frame and so I took their advice and went single-ply. not sure if the roof covering plays a part for green roofs either but as the same roofer who did the single-ply did the green roof I just let him take the lead and recommend the best products to use.

[Mears]

Thanks for the comparison @PeterW

 

I'll be using this system when I get around to it https://www.green-tech.co.uk/green-roofs-and-living-walls/green-roof-systems/green-roof-sedum/sedum-green-roof-trays

 

Approximately 50kg/m² saturated weight