How to Install a Green Roof

Many of us are looking for ways to be more environmentally friendly and sustainable in our daily lives. While our personal habits are often the first changes we make, improving your home’s energy efficiency can make a big difference and a great way to do that is with a green roof. Here’s what you need to know about how to install a green roof.

Green roofs can be installed on most buildings

The first thing to note about installing a green roof is that you don’t need a flat roof for it to be possible. While flat roofs are better suited to the construction of a green roof, it is possible to grow a green roof on a pitched roof and they can be created on houses or outbuildings.

On pitched roofs over 20°, the green roof will need to be designed with a system for retaining water and housed within a frame to keep everything in place.

Check the suitability of your current roofing material first

Before you begin the installation, you should check that your current roofing material is suitable and durable enough to support a green roof on top of it. Even a lightweight green roof can weigh between 60 and 150kg per square metre and this weight will temporarily increase during periods of heavy rain. Even a strong, undamaged roof may need an additional layer of waterproofing before a green roof is added.

Extensive green roofs may be able to be done yourself

If your roofing material is appropriate, an extensive green roof may be able to be DIYed. Extensive green roofs are lightweight and do not need additional watering unless there is significantly less rainfall than usual. Extensive green roofs are usually made up of grass, sedum or small flowers, which keep the maintenance requirements and weight low whilst still providing environmental benefits.

Intensive green roofs will require professional assistance

Intensive green roofs are commonly known as roof gardens and are much more complicated projects than extensive green roofs as they can house more complex systems that can include bushes or small trees. These types of green roofs require a much stronger roof to support the system. Intensive green roofs will most likely need a specialist professional to install them.

How to install a green roof

Green roofs are constructed in a layered system, which needs to be adhered to during installation:

  • First, a waterproofing layer must be installed on the roof deck. Some roofs may already have this layer and it can be created from a bitumen membrane, waterproofing liquid or asphalt. In other cases, a layer of pond liner or a similar material can be used.
  • Next, a root barrier must be laid to prevent roots from damaging the roof structure. This layer is usually made from a thin polyethylene plastic membrane.
  • After the root barrier is secured, a drainage membrane must be laid, which allows the excess water to drain and prevents damage to the plants and the roof itself.
  • If the drainage membrane does not have a geotextile filter layer attached, then one will need to be installed to prevent the drainage membrane from filling with soil and substrates.
  • Next, a growing substrate must be laid to allow vegetation to grow on the green roof. This could be soil, but specially designed green roof growing substrates are available which are a mix of organic and aggregate substances designed to facilitate plant growth. Remember that, on pitched roofs, the substrate will need to be housed within a rot-resistant frame to keep it in place.
  • The final step of installing a green roof is to plant the desired vegetation. 

Extensive green roofs will be limited to smaller choices such as grasses, mosses, sedum and wildflowers. Some of these plants can be bought in pre-grown mats that simply need to be installed on top of the substrate. Intensive green roofs have more choice, all the way up to small trees and bushes, but these should still be drought and wind resistant varieties that can handle the British weather.

Now that you know how to install a green roof, you just need to decide where it’s going to go and what you’re going to plant. If you need any further advice on installing a green roof, please don’t hesitate to get in touch.

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