Could You Install a Green Roof?

While it may seem like the latest up and coming trend, the history of green roofing actually dates back to around 500 BC. One of the seven wonders of the world, the Hanging Gardens of Babylon, is a prime example of one of the first green roofs. Built-in what is now Iraq, King Nebuchadnezzar II designed the stunning gardens for his beloved wife. The gardens grew over stone pillars and rooftops reminiscent of his wife’s much-loved homeland.

Vikings used sod and grass as a form of insulation, and this remained a popular way to cover a house in the Middle Ages. Fast forward to the 1700s and 1800s in North America, and you would find prairie settlers using green roofing when building their homes as well. In fact, due to the lack of trees for cabin building, ‘bricks’ were created out of pure sod and then laid roots side up so they would eventually grow into each other, creating a solid foundation. Time travel to early 20th Century Germany and discover urban areas full of flat green roofs. Later in the 1970s, Germany was one of the first countries to attempt to combat the oil crisis by exploring the impact of green roofs on energy conservation efforts. By the mid-1990s, there were more than 3200 acres of the country’s rooftops that were green!

The UK would probably be considered a bit of a late bloomer in the green roof world. Changes are now being seen, though, especially as the development pace ever increases in already cluttered urban areas where city inhabitants welcome the splash of colour. The most extensive green roof in the UK is found atop the Royal Bank of Scotland in Edinburgh. This expanse of greenery covers 1500m2. Other green roofs can be found at the Metropolitan University in Manchester. These are not only aesthetically pleasing but also aim to combat climate change and reduce urban heat. Sheffield planted rooftop safaris in an effort to encourage biodiversity and provide a space for the black redstart to return to the area.

Now in 2021, more and more environmentally-conscious homeowners endeavour to add a green roof to their garden room or shed. Not only can they be beautiful to look at, but they have many other benefits.

By its very nature, a green roof reduces the carbon dioxide impact and produces oxygen; it also helps to reduce the pollutants in the air from entering your garden room. Green roofs act as a form of insulation, helping to cool a room in the summer. While it may sound like it would be a wet mess, the impermeable membrane which is placed down first actually means an adequately installed vegetated roof lasts longer than a conventional one!

Are you thinking about your very own rooftop paradise? It’s great for the environment and can provide some added benefits such as insulation. Here are some of the key considerations you should take into account first.

Types of Green Roof

There are three main types of green roofs;

• Lightweight extensive – this is the simplest type requiring very little maintenance using sedum or stonecrop plants which spread like a mat.
• Extensive – this requires slightly more maintenance consisting of a mixture of stonecrop plants and wildflowers. This mixture supports a lot more wildlife than sedum does on its own.
• Semi-intensive – not for the faint-hearted, this green roof resembles a garden rather than a rooftop decoration. Consisting of a mixture of smaller shrubs, herbs and ornamental plants, you’ll need professional help to construct it and a lot more time for maintaining it.

Quick How-To

• Weight: you will need to ensure the garden room or structure is well built and waterproof and, most importantly, that it can withstand the weight of the green roof. A lightweight extensive green roof will weigh anywhere from 60 to 150kg (that’s about 9 ½ – 23 ½ stone!) per square metre. Of course, rain and snow will increase this weight. If you’re not sure whether the roof would cave in, ask a structural engineer.
• Angle: a green roof can be built on a flat or pitched roof, but ideally not at a greater slope than 10°. They can be made on a roof with a greater angle but will need a frame to prevent them from slipping completely.
• Waterproofing and Protection: you’ll need something like a heavy-duty rubber pond liner to stop the roots (and, of course, water) from creeping through. On top of this lay a plant protection fleece. You can grab both from a local garden centre. If you have a completely flat roof (or up to 5°), you’ll also need to add pea gravel over the fleece to assist with drainage.
• Framing: You’ll need to construct a frame for your green roof from either lightweight metal or rot-proof wood. The frame will need to be as deep as the substrate or soil that you intend to use. This will usually be a minimum of 10cm. You can either nail the corners of the frame together or use L brackets. Don’t forget to add holes to the side of the frame closest to the ground to allow the excess water to drain out.
• Soil: there are speciality lightweight green roof substrates available – we would recommend sourcing this.
• Plants: Now comes the fun – choose either pre-vegetated mats or plant directly. Herbs, wildflowers, grasses and sedum work best. They are hardy and resilient but will still attract a wide variety of wildlife. Just remember, the plants at the bottom will always receive more water than those at the top (pesky gravity!) – keep this in mind when you’re placing your plants!

We hope that these tips can give you some guidance on the best way to have your very own rooftop garden! You could install a living roof on your garden room. If you live in the South East then we would be more than happy to provide a quote on this for you.