Creating Your Own Green Roof

Step 1 : Safety

Check your building is sturdy, waterproof and can take the weight of the green roof. Typically a basic lightweight green roof will weigh between 60 to 150 kg per square metre which will increase when saturated with rain or snow. If you are unsure about the structural loading capacity of your building or shed, consult a structural engineer or architect before you start.

Step 2 : Angle of roof

What angle does my green roof need to be?  Green roofs can be created on flat or pitched roofs.  Ideally, a green roof will go on a slope up to 10° but if it’s on a slope over 20°, make sure you have a frame to stop the green roof from slipping.

Step 3 :  Waterproof

First, a layer of waterproofing needs to be added to your shed or garage. Typically sheds already have a layer of bitumen felt but the best option is to use material like heavy-duty rubber pond liner to prevent water or roots getting through.

Step 4 : Protective Fleece liner

To protect the pond liner during assembly, add a plant protection fleece, which can be purchased in a roll from a local garden center.

Step 5 : Build a frame

Build a frame from rot proof wood or lightweight metal.  The frame needs to be the same depth as the substate (soil), normally 100mm minimum. The frame can be made by simply nailing the corners together or by using ‘L’ brackets to form the corners. This will hold the substrate (soil) and plants in place but will also allow rainwater to drain out to avoid the substrate becoming water logged.

Water needs to be drained from the roof, so ensure holes are added to the side of the frame nearest the ground or alternatively, ensure a 10mm gap between the roof and frame.

Extensive Green roofs don’t need to be deep as the recommended plants such as sedum, wildflowers and herbs don’t root deeply. As a general rule of thumb, it’s best to have a soil depth of at least 100mm.  For example, 60mm of substrate (soil) and 20mm of pre-vegetated mats.

Step 6 : For flat roofs only.. pea gravel!

If your roof is flat (or up to 5°), a thin 10mm layer of pea gravel over the plant protection fleece to ensure water can drain without blockages.

Step 7 : Add soil

Use extensive lightweight green roof substrate designed for sedum or wild flowers which require between 70-200mm depth of substrate to root. The soil needs to be lightweight to reduce the weight applied on the structure.  We highly recommend our lightweight green roof substrate.

Step 8 : Planting!

You can either purchase pre-vegetated mats or plant directly.  Sedum plants, herbs, wild flowers and grasses work best as they are more resilient than most while still attracting a wide range of wildlife. Remember the plants at the top of the roof will receive less water than the plants at the bottom, so make sure this is taken into consideration when planting or laying sedum.