Humans are incredibly good at building things – it’s one of our defining characteristics as a species, after all. But unfortunately, we’re also incredibly good at destroying things, and every building that is erected in a formerly green space destroys the vegetated footprint that was there originally.
While it’s not possible to completely replace what was torn down, one strategy for mitigating the environmental damage – and producing an aesthetically pleasing environment at the same time – is greening your roof. Green roofing refers to growing plants on the roof of your building to both reduce the negative impact of development and produce benefits to your home.
“One strategy for mitigating the
environmental damage – and producing
an aesthetically pleasing environment at
the same time – is greening your roof.”
How Green Roofs Work
To ensure that you have a green roof that performs most optimally, just putting plants on it isn’t enough. Depending on what type of roof you want, you’ll have to do different things. Modern green roofs can be categorized as either ‘extensive’ or ‘intensive’, depending on the planned usage for the roof area and the types of plants you want. (Image source:)
Extensive roofs contain limited plant species, like herbs, mosses, grasses and drought-tolerant plants, and require minimal maintenance to keep them going. They only need a shallow substrate layer of < 10 cm, and usually aren’t publicly accessible.
Intensive roofs have more plant variety, and may include trees and shrubs as well as the hardier plant species that characterize extensive roofs. However, they are usually limited to flat roofs with a substrate layer of > 15 cm, and require a great deal of maintenance, especially since they are usually park-like areas that are open to the public.
Steps to Building a Green Roof
It can be difficult to find a step by step guide to making a green roof, so unless you are experienced in construction, be very careful. The following guide should be used with caution!
- Start by strengthening your roof. The extra weights from the substrate and plant matter could cause damage, especially if you are going for an intensive green roof. Living roofs can weight up to 150 kg/m2, so consider this as you determine the required strength.
- Then consider the substrate you need. Pond liner will keep water from getting to the roof – the last thing you want is leaks. On top of this you can add a root membrane to help drainage, with a layer of gravel above and below it, and then a moisture blanket to keep the moisture in the soil.
- Add wood chips for extra moisture retention and compost and topsoil so that the plans have nutrients and somewhere to grow.
- Once you have your substrate, you can start planting. Hardier plants are best, as you want them to survive (but again, if you are looking to make an intensive roof, you might make a different selection – just be aware of the extra maintenance required).
- After planting, and before the plants spread, you might need to weed the roof space. You will also need to ensure it is kept adequately watered.
Green Roof Benefits
So aside from looking nice and reclaiming development space, why use a green roof at all? Well, there are actually several environmental, economic, and social benefits. For example, as long as you keep your eavestroughs clear, they can help to improve stormwater management by reducing runoff and improve water quality. They can reduce noise and air pollution and sequester carbon, and also conserve energy and mitigate the urban heat island effect.
In terms of economic benefits, they increase the longevity of your roof lining (because UV light does not damage the roof surface as much as it does with no plants on it, and the lining is also protected from large temperature variations), and increase return on investment compared with traditional roofs.
Stormwater mitigation is probably the most important benefit, because there are so many impervious surfaces in urban areas that runoff is a huge problem – it makes flooding worse, increases erosion, and means that more water must be treated to make it drinkable. So the absorption of stormwater by green roofs, and its slow release over several hours, greatly helps in the management of this runoff. Such roofs can absorb between 60 and 100 per cent of the stormwater they receive, so this benefit really cannot be overstated.
Enjoy your green roof!
Have you considered greening your roof?
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