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Green roofs: how and why you should build one this year

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Gardeners and eco-warriors have been urged to install green roofs this year, to help tackle the effects of climate change. Green-fingered gurus from GardenBuildingsDirect.co.uk have revealed how green roofs can benefit families’ outdoor spaces by providing habitats for wildlife, preventing gutters from overflowing, and reducing carbon emissions.

A green roof is a roof that supports the growth of grass or plants of some sort. They’re most commonly planted onto shed roofs, providing additional growing space, texture and colour to your garden, all whilst providing more room for local wildlife. They’ve grown in popularity over the past decade, not least because they expand your gardening space by adding a beneficial and interesting feature to the garden. Green roofs also help in a small but significant way to reducing carbon emissions, whilst providing sound and heat insulation for your shed.

There are two types of green roof – intensive and extensive. An intensive green roof will require more maintenance, as it supports a variety of plants and utilises water irrigation systems. Extensive roofs require much less maintenance, but the type of planting is limited to drought-tolerant and weather-hardy plants. A spokesperson for GardenBuildingsDirect.co.uk said: “Installing a green roof to your garden building, shed or storage area is a fantastic way to transform a dull, functional space into something that’s living, breathing and looks great too. “By adding a green roof, you’ll be able to reclaim some of the space your shed or outhouse has taken up, whilst also improving air quality and encouraging wildlife into your garden. “They can provide a fabulous habitat for wildlife, whilst helping to slow water runoff and prevent gutters from overflowing too – it really is a win-win situation! “Plus, green roofs only need maintaining twice a year – simply ensure drainage outlets remain clear, plants are watered in the dry season, and bare areas are re-planted.”

Here are GardenBuildingsDirect.co.uk’s tips to building a green roof:

1. Preparation

Before you begin, you need to make sure that your existing shed roof is strong enough to take any extra weight. 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. Check that there are no areas of damp, rotting wood, splits or holes. Make sure that the roof is also waterproofed – an additional waterproof layer may be necessary if you’re in doubt.

2. Angle

What angle does your green roof need to be? A green roof can be constructed on a flat roof. However, shed roofs most commonly have pitched roofs. Ideally, the pitch of the green roof should be around 9-10 degrees, as this is not only best for the plants but also reduces the need for retention to stop the roof sliding or slipping. If it’s on a slope over 20 degrees, make sure you have a frame to stop the green roof from slipping.

3. Lining

To start, you should put down a layer of membrane. This can be a 300-micron damp proof liner, or you can opt for pond liner. Make sure that this layer covers all edges of the shed to avoid any water from seeping in.

4. Layer

Next, put down a layer of weed suppressing membrane. This helps to contain the roots of the plants so that they don’t try to grow down and through into the bottom layers. Once you’ve secured this, you’ll need a layer that will help to retain moisture. This can be achieved by simply laying down old blankets.

5. Frame

Build a frame from rot-proof wood or a lightweight metal. The frame can be made by simply nailing the corners together and should be the same depth as the substrate (soil) – normally 100mm minimum. This will hold the soil and plants in place but will also allow rainwater to drain out, so it doesn’t become waterlogged. Ensure holes are added to the side of the frame nearest the ground so that water can drain out or alternatively, ensure a 10mm gap between the roof and frame.

6. Pea gravel

If your roof is flat or only has around a 5-degree angle, a thin layer of pea gravel over the plant protection fleece will ensure water can drain without blockages.

7. Soil

Use a lightweight soil or substrate to reduce the weight being applied on the structure.

8. Planting

When it comes to planting your new green roof, sedum plants, herbs, wildflowers and grasses work best as they are more resilient, while still attractive to a wide range of wildlife. If you have a pitched roof, remember that the plants at the top will receive less water than those at the bottom, so take that into consideration when planting.

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