What types of green roofs are there?
There are two types of green roofs, namely intensive and extensive. Both have various benefits and disadvantages to those who wish to build them, and below is a more in-depth explanation of both:
This is what you could call a “roof garden”, and has deep layers of growing medium which support a large range of landscaping elements such as shrubs, small trees, lawns and even bodies of water. They require a deep layer of growing medium, which can weigh up to 36-68 kilograms per square foot. Some intensive green roofs are suitable for supporting benches, so people can access them and enjoy the artistically landscaped surroundings.
These have a much shallower level of growing medium, and are easier to maintain. They are not suitable to the range of plants that intensive green roofs are, but can support some such as succulents and other low-growing vegetation. These roofs require less maintenance, but because they do not have as solid a structure, usually are not in place for people to access.
What does a green roof require?
Building a green roof is no small undertaking, but the benefits are massive. If you are considering building a green roof, there are several aspects that must be taken into consideration, including:
The sturdiness of the roof structure:
Green roofs need to be able to support 11 to 45kg more load per square metre than normal roofs, and should be relatively flat in structure.
The reliability of the waterproofing membrane:
The waterproofing material needs to be elastic, in order to withstand the movement of the building, must be non-biodegradable, and needs to be strong enough to withstand root penetration.
The toughness of the protection fabric:
This synthetic fabric protects the waterproofing membrane from mechanical damage during any construction or maintenance. For ultimate durability, it should weigh from 500 to 900 grams per square meter.
Green roof soil is unlike normal soil, as it needs to be lightweight, have good water storage capabilities, have a low organic content and have good particle distribution.
Are the plants appropriate?
Because green roof plants need to be able to survive in the green roof environment – which can be hot and dry – the best plants to use include succulents and herbs for thinner green roofs.
Whether you are interested in an intensive and landscaped “roof garden” or a simple extensive roof covering, figuring out what a green roof requires is the most important first step of the process!