Sedum roof build-up

4 min read

Sedum Roof Build-Up – In this blogpost, we’re looking at sedum roof build-up and how it affects the sustainability of a green roof.

What is it that makes a sedum green roof succeed or fail?

Well, truthfully, there are many factors.  Design, installation, maintenance, and sometimes (but rarely) just plain bad luck.  But as a rule of thumb, understanding the layers in the build-up and how they work together is the way to ensure that a sedum green roof.  Mixing and matching elements from different build-ups is risky.  Each manufacturer will have spent a lot of time and money to make sure that the components of their green roof build-up work together.  To mix and match is like trying to put Land Rover parts into a mini – it might work – but it probably won’t.

Sedum Roof Build-Up – Designing a sedum roof

If the aspect is right (plenty of sunlight, not too steep a slope, protected from cruel winds); and the correct build-up has been properly installed.  A sedum green roof should thrive with just a simple maintenance regime.

What components are needed?

There’s more to a green roof than just mud and seeds.  Sedums are hardy little plants with big hearts and they’ll try to grow anywhere.  But two things they cannot tolerate are poor drainage and shade.

Shade is down to the aspect of the roof and its proximity to taller buildings and trees.  It cannot be controlled by the green roof build-up.

Drainage however is intrinsic to the design of a sedum roof.

A sedum green roof needs a drainage layer, some means of retaining enough rainwater for the plants to survive, growing medium and of course, sedum plants.

Sedum green roof build-up.  From the bottom upwards we have:

  • waterproofing;
  • polyethene to protect waterproofing;
  • drainage mat,
  • water retention mat;
  • Enviromat sedum matting

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Sedum roof build-up – Managing rainwater on a green roof

Most roofs have some sort of slope to them.  Even a “flat” roof has a bit of a fall to allow for drainage.  This is vital.  If the subject of your planned green roof has puddles laying on it for more than 24 hours after a rainstorm, this needs to be addressed before adding the green roof build-up.

The green roof build-up sits on top of conventional waterproofing.  Make sure that’s watertight before installing any of the green roof layers.

For a “flat” roof.  That is to say one where the slope is less than three degrees.  It’s important to start your green roof build-up with a layer of drainage matting.  If the slope is greater than three degrees, this layer isn’t needed.

Sedum roof build-up – Irrigation vs water retention

The sedums on your green roof are incredibly drought tolerant and they hate having soggy feet.  But, they are living things and they do need to have access to water.  Just not too much of it.

There are 2 ways of tackling this.

  1. Install an irrigation system so that you can water the plants during long periods of drought (you will need to water them regularly for the first few weeks after installation anyway)
  2. Put a layer of water retentive material up on the roof so that the plants have some water available but the substrate is not sodden.

Option 2 could involve a deep layer of growing medium or it could be a matter of using water retention matting.

Deep substrate is preferable.  However, it’s not easy to lift onto the roof and once it’s there it can exert quite a heavy load on the building.  If the building has been designed to take the weight – excellent.  If you’re not sure – get expert advice.

Water retention matting can normally be bought at the same time as sedum matting,  In fact Enviromat All-In-One Sedum Matting has the water retention matting sewn to the back of the sedum mat.  That saves you a job!

The final flourish – sedum plants

If you’re using the substrate system then you can hydroseed or plug plant your sedums directly into the substrate if you want to.  Or, you can use a sedum blanket (aka sedum matting) which comes with the plants already established and growing well.  All you have to do is roll out the matting and water it in.  It can go directly on top of substrate, or directly onto the drainage mat and water retention mat.  Simple.

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