Over 40% of the Dutch people live in cities and the expectations are that this number will continue to rise. Although city-dwellers have made a conscious decision to live in the city, they do need green recreation areas. In point of fact: they would all prefer to make use of the green spaces in the city at the same time. So, we have an urban area with a growing number of inhabitants and an increasing amount of pressure on the available space. The solution can be found above our field of vision: our roofs. Green roofs are the perfect way to create green areas without using extra space.
Green islands in the city
For centuries people have made their roofs green. Think for instance of the world wonder ‘the hanging gardens of Babylon’, or the Indian peoples in the Andes covering their roofs with turves. In Scandinavia, Canada and Germany green roofs can be seen now for many years. And in the Netherlands we only just start realising that green roofs are the future.
Green roofs can play a significant role in improving the air quality. Vegetation filters out small particles, nitrogen dioxide and soot and this is beneficiary to the public health. This is needed: 4,000 to 7,500 people die due to the consequences of air pollution by road traffic on a yearly basis. If more buildings near motorways would be equipped with a green roof, this would mean very beneficiary for public health.
Yet another problem of our times. Heavy rainfall is not a new thing in itself, not even in northwestern Europe. But generally speaking, experts do expect fickle weather conditions to happen more often as a result of climate change, with the consequence of too much rainwater. Green roofs can keep the rain in its place, i.e. on the roof, for a while. Subsequently, the moisture will evaporate over time, just like in nature.
Like any addition to the ‘green’ in urban area, green roofs also offer housing to a number of insects that would have no chance of survival in a brick desert. When maintained wisely, green roofs will also contribute to improving biodiversity.
For centuries we have been used to see the city as a collection of facades and roofs. Roofs especially – covered in roofing tiles or slate shingles – are iconic for the city. In an aesthetic sense there is nothing wrong with this image. But office buildings, often having ugly roofs covered in bitumen, do not really contribute to an attractive cityscape. New development of offices and flats, but villas as well, will offer an opportunity to have more green in the city. With a beautiful view as an added bonus.
Heat and cold
An important motive to cover a roof – that in itself should be waterproof of course and protect the inhabitants from the elements – with an extra layer of dirt and vegetation is the protection against heat and cold. In short: isolation. This was the motive behind the above-mentioned hanging gardens of Babylon, besides aesthetic arguments. In our neighbouring country, Germany, green roofs are used on a large scale today, as a way to save energy.
The question arises why the Netherlands, a very energy-conscious country, sees so little green roofs, even though a number of cities (like Amsterdam and Rotterdam) have formulated a green-roofs policy. Furthermore, we can safely assume that solutions have been thought out for all objections we could think of (weight, maintenance, et cetera). But the fear is that the dislike the Dutch people have been brought up with for ‘plaggenhutten’ (turf huts) has destroyed the image of the green roof. It started in old children’s books, where such turf huts were used as metaphors for backwardness and poverty. But those times are in the past now, thankfully.
Compensation and saving
Those who look into the matter will soon discover that modern councilmen and –women are the ones who are making use green roofs, especially in those places where trees and shrubs have been sacrificed for building sites and need to be compensated. But also because they want to reduce the ever increasing use of energy, mostly for heating but also for cooling. Calculations have shown that green roofs will be cheaper than more classical forms of roof covering, if a certain number of preconditions are upheld. Those benefits will only get bigger with the steady rise of gas prices.
Builders, officials and citizens who are interested, can look at the various aspects and possibilities of green roofs with the booklet ‘Green above everything else’, published by TripleE productions: www.tripleee.nl. A lot of the info on this web site is based on this book.