You are here: Green roofs: a growing trend

Green roofs are sprouting up across the UK. They can range from rooftop gardens with shrubs and water features to rolled-out green carpets of perennials and low-growing grasses. A green roof will boost your home’s eco-friendly credentials.

Green Roof
Green Roof

Image supplied by Green Roofs Direct

What is a green roof?

Whether it’s a house extension, garden studio or shed, a green roof is one that is completely or partially covered in plants. Green roofs are also known as living roofs.

There are two types of green roof: intensive and extensive. Intensive green roofs, or rooftop gardens, can be accessible and include shrubs, perennials, water features and even small trees. Extensive green roofs, meanwhile, are thinner, lighter versions, more for visual effect rather than walking on. Low-maintenance mosses, wildflowers and low-growing grass are common choices for extensive roofs that can be flat or sloped.

How do I know if my home is suited to a green roof?

Flat and shallower roofs tend to be the most suitable. If the slope of the roof is over 18 degrees, it’s a good idea to get specialist advice as there may be extra design issues to consider. The other key question, is can the existing structure take the extra weight of rain-sodden compost and plants or does it need to be strengthened? Simple lightweight green roofs weigh between 60-150 kg/m2. If you’re unsure, get a structural engineer or surveyor to check the loading your roof can take.  

Access to the roof is important if the plants need watering.  Sedum, a succulent perennial plant, is a good choice for a green roof with no access. The stems and leaves store water, so it’s drought tolerant.

How do you build a green roof?

There is a lot more to building a green roof than just piling earth atop of a building with a sprinkling of seeds. A well-designed green roof is built up of several layers. Typically, it includes a waterproof/root-proof membrane, drainage board, filter layer, substrate (compost) and vegetation plus edging to keep it all in place.

That said, there are kits to make DIY installation easier, such as sedum plant matting that includes drainage and waterproof backing. It comes in a roll and you simply place it on top of the roof and fix it in place with batons.

Other options include green roof trays which clip together and include all the required layers in one package, rather like a shallow planter. A sedum roof tray costs £39 per m2 from Green Rooftops – prices correct in October 2019.  The brown wildflower and fleece Grufekit tile, from UK Flat Roofing, promises easy installation and instant colour at £44.99 per m2, excluding VAT -

How does it add visual appeal?

Frequently, with a single-storey home extension you can end up looking down onto a big area of grey or black roof from the first-floor windows. Imagine instead seeing a green roof with grass, lavender and wildflowers that attracts, birds, bees and butterflies? A green roof can work particularly well in rear home extensions to reinstate garden space lost to development.

Pros

One of the main advantages is aesthetic; a living roof covered in wildflower and sedum is lot more attractive than dull felt or grey asphalt surface. Green roof materials help reduce water run-off and flooding as part of sustainable urban drainage systems (SUDS). They have an insulating effect, helping to reduce the amount of energy needed to heat the building in winter and keep it cool in summer. They also cut noise levels, provide habitats for wildlife and reduce air pollution by absorbing CO2. Plus, you won’t hear pigeons walking on it.

Cons

Of course, there are a few negatives. Green roofs are slightly more expensive than the traditional option. Without a doubt, green roofs are heavier than a standard roof. Some buildings can’t be retrofitted with certain kinds of green roof because the weight loads will exceed the permitted static loading. Typically, the addition of a green roof will add between 50 and 200kg per m2 to a rooftop. That said, there are ultra-light weight sedum blankets systems available, for example from Green Roofs Direct. Green roofs can be affected by drought and waterlogging.

Can you have solar panels on a green roof?

Environmentally conscious homeowners may feel they have to choose between solar panels or a green roof.  But there are systems available that combine the two.  Green roof PV or biosolar systems integrate the energy-generating capability of solar technology with the habitat creation benefits of green roof systems. In contrast to a typical flat roof PV installation, the panels are placed at a steeper angle (15 degrees rather than 10 degrees). This extra space allows vegetation to spread underneath the panels with access to light and moisture. Obviously, the system needs to be well-designed, so the plants don’t overgrow the panels and put them in the shade. A biosolar system will require expert installation.

Plants

Picking the right plants is essential for your green roof to survive and thrive. Many suppliers now offer green roof seed mixes specially chosen to grow in very little soil (50mm to 150 mm) and cope with droughts. They include sedums – evergreen alpine plants used to harsh, elevated conditions which provide coverage all year round. Wildflowers, such as poppies, Cows Slip, rockrose and thyme, can survive in low nutrient substrates and provide colour. Green roofs may also be planted with heather and lavender to create a rooftop garden.

The vegetation can come in pre-planted mats or blankets, usually sedum or wildflowers. Alternatively, you can plant cuttings or seedings.  

Green roofs are attractive and have many environmental benefits. As bird and bee populations plummet across the planet, this is an area where homeowners can step up.

The eco-friendly credentials of green roofs are recognised by government at a local and national level. A green roof in a planning application should help win approval.

If you are thinking of improving your home, you may find some of these services useful: