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There are two important things to consider when thinking about transforming an extension, garage or shed roof: the state of the existing waterproofing and the structural capacity of the building in question. Sheds and garages will need some structural uplift and extensions may be limited to very lightweight green roofs systems. It is also important that the waterproofing is not only fit for purpose in terms of not leaking but that is also a root-protected membrane.

There is not room to go into detail about the construction of a green roof on any of these buildings but our gives a full and comprehensive guide to constructing green roofs on sheds, garages and small buildings.

The main point is the more growing medium you can get on the roof the greater the selection of plants that can be used. And that is what is really interesting whether you are a gardener or someone who just wishes to add colour and wildlife value to your home and garden.

Thyme

As a nature conservationist, I tend toward native wildflowers. Most of the dry grasslands flowers will grow on a green roof with a depth of about 100 -150mm. Of course sedums, sempervivums and other succulents can also be planted to give some ‘evergreen’ during the winter.

I am particularly fond of the our native wild herbs because they can give a lot aromatic value even through the winter. The pungency of a Mediterranean hill brought to your garden. When my colleague John Little, builds a green roof on a school shed or outdoor classroom often asks the children to bring in ‘rockery’ plants to add to the green roof and many of these plants thrive readily in the stressed environment on a green roof.

Another series of plants to consider are bulbs. Even on some of our big city green roofs we have planted allium, muscari, crocuses, dwarf irises and narcissus. Chives and grape Hyacinth are well-known green roof plants and the others have all been very successful, giving both a splash of colour and an early nectar source for emerging bumblebees and solitary bees when they are most vulnerable.

Dwarf Iris

As yet we haven’t tried any of species of squills, especially those that flower in the autumn but I have colleagues in Greece that have these growing on their roofs, as well as cyclamens, both of which would be an important late nectar source for pollinators. Hopefully we will plant some in the near future.

In my experience plant small but which I mean ensure that whatever you plant into the roof has a small root ball. The smaller the plant, the better it will be to survive the stressed conditions on the roof. Don’t be put off by all the technical jargon – green roofs are relatively simple and confidence is the main problem so have a go.

is a well known green roof campaigner, designer, public speaker and is currently the President of the European Federation of Green Roof Associations.