Creating a Green Roof on Shed or Garage

What is a Green Roof?

Green roofs are increasingly popular features atop houses, sheds, and garages across Britain. As well as providing unconventional and unexpected slivers of beauty amongst mundane architecture, they help to improve biodiversity in urban areas, attract local wildlife, offset carbon emissions, and even provide insulation and flood protection for nearby structures. 

There are two types of green roofs. Intensive roof gardens tend to be created on a large, complex, and commercial scale (think rooftop gardens perched above city skyscrapers). Extensive green roofs, however, are much better suited to your garden shed or garage. They are low maintenance, uncomplicated, and lightweight by design.  

How to fit a Green Roof?

Structural Integrity and Specifications

You will need to check out the structural integrity of your shed or garage first, to ensure it can support the extra weight of the garden. Of course, flat roofs are preferable, but any slope of fewer than 30 degrees is suitable for a green roof. If your chosen roof is slightly sloped, you may need to build a supporting frame to prevent the garden from slipping down the roof, particularly after heavy rainfall. 

Your roof will need to receive both adequate sunlight and rainfall for plants to thrive, and you will need to access your garden once or twice a year for essential maintenance, so ensure you have a safe way of getting up on top of your shed or garage. 

Layers 

Extensive green roofs need to be constructed in layers. Firstly, they require a waterproof layer or membrane to protect the structure beneath. This could be an existing layer of bitumen or similar, or you may need to install something more hardwearing.

Next, you will need a root barrier to protect the structure from root damage. A polyurethane sheet or weed-proof fabric should do the trick. It is crucial to install a drainage layer to prevent your roof from becoming waterlogged. Drainage mats are readily available to purchase in a variety of size specifications and usually feature capillaries or perforations which allow water to flow freely.

Next, you will need a layer of lightweight, nutrient-rich, free-draining substrate as the growing medium for your plants. This should be between 50 and 100 mm deep. Finally, you can install your vegetation or sow seeds over the substrate layer. 

At Chargrace Soils, we have all the materials to get started on your green roof.

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Suitable Plants

The idea is to create a garden that only needs tending once or twice a year, to weed, feed, replenish any dead areas, and check on the drainage system. Occasionally, during droughts, plants may require extra watering. Low maintenance and shallow-rooted plants are the keys to success here. Try to mix your species, as this improves biodiversity, adds interest, and prevents disease or nutrient deficiency.

Sedum blankets are by far the most commonly used vegetation in roof gardens. These hardy succulents provide excellent coverage with minimal food, water, and sunlight requirements, whilst providing pretty blooms. Native wildflowers are another great choice for roof gardens, as they require almost no maintenance, will attract plenty of local wildlife and will provide a stunning, colourful display in the summer months. If your shed or garage roof is not very easily accessible, you could even consider creating a kitchen garden by growing shallow-rooted, hardy herbs such as Rosemary, Chive, or Thyme.