Green roofs – an expert guide to growing a living roof

Living roofs, also known as green roofs, have seen a spike in popularity in recent years, and for good reason. Not only do they provide a decorative addition to the functional structures in your backyard, helping them to blend in with the planting scheme, but they also have unbound environmental benefits. 

You needn’t be building or putting on an addition for this eco home improvement to be part of your plans. A green roof can be added in some cases to an existing house, a garage, or a backyard building. But these planted roofs are far more than a great way to improve the view. 

‘Green roofs are the most biophilic roofing system there is,’ says Karl Harrison, Trex(opens in new tab) decking pro and founder of Karl Harrison Design(opens in new tab). ‘They are natural, colourful, biodiverse and contribute to the ecological footprint of any building supporting this type of roof. They attenuate the rain on the roof flowing into the water waste allowing for easier water management, and this is done by absorption. Plants need water to survive and green roofs retain most of the rain that falls on them.

HOW DO GREEN ROOFS WORK?

Green roofs are a great way to incorporate wildlife garden ideas into your plot but they also provide an aesthetic and practical addition to your backyard. 

‘On top of this is laid a protection and moisture fleece. Followed by the drainage and water-retention board, which acts as a reservoir of rainwater for the plants while allowing excess to flow off,’ explains James Beattie from Pritchard & Pritchard(opens in new tab). This could be plastic, but there are natural options as well, including gravel and even shells. 

A filter sheet goes above the drainage layer, which prevents soil from washing out and keeps the reservoir clear of debris. A downspout is also necessary to take excess water away from the roof, but rain chains could be used in place of conventional guttering. 

The perimeter of a green roof generally features an area of shingles, which will need to be kept free of vegetation to allow water to move through it and be taken off the roof.

‘Next comes the substrate, which is a specially formulated light-weight growing medium (much lighter than soil); the depth (and weight) varies with the type of planting,’ explains James Beattie from Green Roofs. Because a green roof does not have a replenishing soil source like a garden on the ground, you will periodically need to add more soil to the green roof due to loss from wind or rainwater. You’ll also need to pull any weeds that make their way onto the roof.

If your roof is inaccessible or makes it hazardous to do these tasks yourself, you’ll want to hire a professional to do it for you. 

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