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Green roof options…

Monday, April 16, 2012 at 10:39

‘Green roof options. ‘ has been written on behalf of Notcutts by Claire Potter of Claire Potter Design. We believe that this is an interesting topic that will offer you, our readers an insight into how beautiful and sustainable a roof can be.

Over the last few years the green roof has gone from a relatively unknown construction feature in the UK to a standard mark for ecologically minded new building. But for those of us who want to recreate our own piece of emerald in the sky, what are the options? The first step is to look at your roof. This seems rather obvious, but the pitch of your roof will determine the type of system you will be able to use. Typically, the shallower the pitch of the roof, the more options you will have when it comes to the type of system and the plants you can grow.

The second step is to talk to your local Planning Authority to check whether planning permission is required for your works. If planning is indeed required, it is worth finding a suitable green roof specialist to advise of the type of system that would best suit your roof as they may be able to put together all the drawings for your application, along with the very important structural and waterproofing calculations.

Green roofs, while beautiful, can be very heavy beasts weighing anything from 50kg per square metre to over 150kg per square metre and it is essential that a qualified Structural Engineer is consulted at the earliest stages of the project to ensure that the proposed system can be supported by the existing building, or whether additional support would be required.

So once the structure and system are decided what are the planting options for a green roof?

To some degree this depends on the type of system you are installing, but to break it down into the most common in the UK the general options are:

- Sedum

- Grassed

- Wildflower meadow

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The most common seen in the UK is the sedum roof as the plants are hardy, evergreen and can cope with fluctuating water levels. They also require very little growing medium, so the overall weight tends to be a great deal lower than other systems. They do not need mowing and tend to stay at a height of 10cm or under, so they are relatively compact and look very neat. Colours vary from lime green to bright red, so if you are so inclined you can even grow a pattern into your roof with plants being inserted individually or through rolled sedum mats which create an instant green roof.

Whilst generally considered the lowest maintenance solution for a green roof, the sedum option is not the most beneficial for wildlife as there is not a huge range of plants, so if biodiversity is your main concern and your roof will support it, the grassed or wildflower meadow could be the better option.

These systems are a great deal heavier as the soil and substrate depth is deeper and they are generally only applied to shallower or flat pitched roofs so the weight does not slip down the structure, although steeper pitched grass roofs are sometimes seen in Europe.

Wildflower and grassed roofs tend to look a little wilder and unlike their sedum cousins they do need cutting, but they will support a larger range of wildlife through their variation in flowering times, nectar levels and food plants for larvae. They can look a little flat in the winter, but conversely they can be a riot of colour in the summer, so there is also the aesthetic element to consider.

Another option which is more common in Europe but is sometimes seen on a small scale in the UK is the herb roof harnessing the drought tolerant characteristics of the sedum roof and the biodiversity of the grass roof. Thymes and marjoram are excellent for this type of planting as they thrive on almost nothing, produce flowers that bees love and smell fantastic. We have created green shed roofs using this type of planting, which have been incredibly successful and can be great solutions for car port roofs, porches and garages as well as garden buildings just remember to check that the structure is strong enough for the system.

Creating a green roof is something to be planned, but with the right system and planting it can not only look beautiful, it can improve the thermal efficiency of your house by adding an insulating layer to your roof and support your local wildlife too.

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