Roofs from necessary evil to functional elements - 19/04/2011

roof functional element

The basic concept of a roof is quite simple: it needs to prevent you from getting cold in winter and it has to keep your things dry when it’s raining. So we make roofs water-tight and, if possible, we insulate them.

However, Dutch cities are getting more condensed. This means that we realise more living, working and accommodation functions within the existing city boundaries. “There is no more space” or “Now there isn’t any space left for green”, people often say. But seen from the air there is 350 million m2 of flat roof surface available. This number even increases by 10 to 20 million m2 every year. The often heavy roofs do not add anything useful to the city in itself, except for a lot of extra heat in summer.

Many steps are taken at the moment to stimulate the functional use of the Dutch roof landscape. There are, for example, solutions with solar cells (function: generation of energy), and there are different types of functional ‘green roofs’ (functions: urban cooling, water storage and re-use, room for biodiversity, decreased cost of air conditioning in summer, and air quality improvement). Urban Tree Tops, developed by SHFT, is one of these.

In the meantime, however, we find ourselves at another crossroads of innovation. Can those functions be combined, in order to make maximum use of the roof? Research has shown that solar cells yield more energy when environment temperatures are low, and as it turns out, it is a green roof in particular that yearly lowers the environmental temperature by 6 to 8 degrees Celcius on average, research in the USA and Germany has demonstrated.

A new challenge for actual practice: solar cells do not like the shade of plants, and plants do not like the shade of solar cells. Yet another analogy with the forest: every branch wants to be the uppermost one in the treetop so that it will catch as much sunlight as possible.

In order to find a solution to this, SHFT has been working hard – in cooperation with Knooppunt Innovatief Groen [central organisation for sharing knowledge and experience in the field of innovative green] – on the design of a roof that combines all functions and looks pleasant too. The set-up of the roof is such that the various functions can be measured and registered, in order to be able to validate the efficiency claims in the end. After all, also for you we want to be able to make objective calculations regarding investments, output and cost-recovery time.

This solution needs to be tested in actual practice. If you consider having your roof made ‘functionally green’, this innovative roof is a good option for you. For more information, please contact Joris Voeten (