Sedum Matting & Sedum Trays – There are a whole host of benefits to a sedum green roof as I’m sure you already know. But how do you create a sedum roof and what does it cost?
Looking around the internet for ideas, it seems as though there are three possibilities.
- Plug plants
- Sedum Matting
- Sedum Trays
Plug plants are great in that you have full control over which species you plant and where. They’re ideal for creating swathes of colour and for putting patterns on your roof. They do take longer to plant and they will need regular weeding for the first year or two. That makes plug plants a different animal to the other two alternatives.
Sedum matting and sedum trays are pre-grown so you can’t make patterns but you do have instant cover.
In this blog, I’m going to compare and contrast sedum mats and pre-grown sedum trays.
Weight Considerations
The first consideration with any green roof should always be “is the building strong enough?” Weight is important and sedum roofs are often specified because the plants need very little growing medium. That means they weigh a lot less than wild flower roofs or intensive green roofs.
One supplier of sedum trays lists the weight of their green roof build-up as 48g/m2
The saturated weight of Enviromat sedum matting is just 34Kg per square metre. Add in a layer of water retention matting at with a wet weight of 9Kg/m2 and the total comes to 43Kg/m2
What you MUST remember to do though, is add on what is known as “live loading”. That’s allowing for a person (or people) to walk on the roof installing and maintaining it. It also allows for temporary extra weight such as snow.
For either build-up, it would be fair to expect your roof to carry at least 120Kg per square metre.
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Ease of Installation
Here, I have to confess I’ve never installed a green roof with my own hands. I have sat back and watched other people doing it and I’ve listened to plenty of tales from green roof installers.
Enviromat sedum matting roofs are easy to install. Especially if edgings are already in place. It’s just a matter of unrolling the layers and trimming them to size. The matting is easy to trim round drainage outlets, air conditioning units, walkways, curves, corners and anything else that might be up on the roof.
Trays – well if your roof is flat and even with no obstacles, they look to be easy to install too. I can’t imagine that they can be trimmed though. I guess you have to work around that. It is good that there are no layers to fiddle about with or get wrong. From that point of view it’s all very simple.
The tricky bit is getting the materials onto the roof. That’s the same for both build-ups though.
Ease of Maintenance
Sedums are so easy to maintain it’s unreal. Just one feed a year, occasionally some weeding and perhaps patching up bare areas from time to time.
Once a sedum roof is established it doesn’t matter how it was built, the maintenance is pretty similar.
For either of these systems, it should be relatively simple to repair bare patches using cuttings.
What is difficult to do with a green roof is repair the waterproofing or any structures beneath the green roof build-up. That’s why we nag our customers to be 110% sure their waterproofing is in good condition before they add any other layers. However, either the trays or the mats should be easy to lift up and move if you ever do need to access the waterproofing.
Cost comparison
At the time of writing, the UK supplier for sedum trays was quoting £65/m2 for their green roof build-up. Now that doesn’t include VAT and I’m not sure if delivery is included in the price either.
Enviromat Sedum Matting green roof kit for a pitched roof came in at £36.24 including VAT. There’s no drainage mat in this kit – you need to allow another £10/m2 or so for that if you are creating a flat sedum roof.
Sedum roof build-up 
Sedum roof construction 
