Creating Your Own Green Roof
Green roofs are becoming increasingly popular in urban areas to provide green space and aesthetic diversity to a built up landscape. They provide many benefits such as improving air quality, providing a fabulous habitat for wildlife, slowing water runoff and preventing gutters from overflowing.
Small projects such as garden sheds and garage roofs can be undertaken by virtually anyone. Adding a green roof area to your home or garden does not only aesthetically improve your garden, but provides a great tool for assisting in tackling the effects of climate change.
There are three types of green roofs;
1. Lightweight Extensive - the simplest roof type that is very low maintenance using sedum plant.
2. Extensive - the one we like! Using a mixture of sedum and wild flowers. Supports more wildlife than sedum alone.
3. Semi-intensive- more like a garden than a roof top. Using a mixture of ornamental plants, herbs and small shrubs. High maintenance and requires professional help to construct.
Step by Step Guide
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 roofWhat 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 7 : Planting!
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.
Did you know?
- Green roofs decrease flood risks by retaining water, decreasing the amount of water that reaches urban drain areas.
- Green roofs help retain heat in a building by insulating the roof during the winter. In summer a green roof will also absorb sun’s rays to keep the inside cool. A natural air conditioner that could work wonders for your garage.
- Green Roofs can attract wildlife to your area. If you have a small garden any extra planting space shouldn’t go amiss, research what you wish to attract and plant relevant flowers to attract them.
- Green roofs only need maintaining twice a year – ensure drainage outlets remain clear, plants are watered in the dry season, and bare areas are re-planted.
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Intensive Lightweight Soil - A soil based mix originally designed for the landscape market to be used in roof garden projects where a lightweight but nutritious and free draining growing media is required, now available for use in the garden environment. Can be used in tubs, pots, hanging baskets and beds where moisture retention and good percolation is required. Can even be used on the garage roof if you want to really impress the neighbours!
Extensive Lightweight Substrate - A substrate designed to be used on roof garden areas where a lightweight and free draining growing media is required. This low nutrient compost can be used all year round for garden and roof planting projects where a lighter substrate is required for sedum or wild flower applications