Andreas Späth

Let’s green our rooftops

2015-04-07 09:28

Andreas Wilson-Späth

If you’ve ever seen an aerial photograph looking down onto any South African city centre, whether it’s Johannesburg, Pretoria, Durban or Cape Town, you would have been struck by the vast expanse of flat, grey concrete landscape, only interrupted by the odd lift shaft. Acres of wasted, unproductive space in some of the most sought-after areas of the country.

As an environmentalist, my first instinct is to suggest that all of this bare real estate should be covered with solar electricity panels, rainwater collection systems and solar water heaters, all of which are great ideas, but there is a different option that is increasingly recognised as a valuable alternative with many environmental benefits: green roofs.

The concept is simple and the technology well established. Instead of covering the flat roofs of inner city structures with heat absorbing concrete or asphalt, green roofs add a layer of living plants to the top of buildings. They typically include high quality water proofing provisions and ways to prevent structural damage from roots, as well as water drainage and filtration systems, a light-weight growing medium and, of course, the plants themselves.

Why bother? Well, there are a number of very compelling environmental, social, public health and economic benefits from green roofs:

- They improve the energy efficiency of buildings, reducing the need for heating in winter and air-conditioning in summer. Green roofs provide an excellent insulation layer that can lead to substantial savings in energy and cost. According to a group of Spanish researchers, roofs covered by high-density vegetation are up to 60% more effective in passively cooling buildings than conventional roofs. Other studies have shown that energy consumption from summer air-conditioning can be reduced by over 75%.

- Green roofs increase and sustain biodiversity, providing urban habitats for indigenous plant and animal species.

- By capturing airborne particulate pollutants and dust, absorbing noxious gases and carbon dioxide, and breathing oxygen, green roofs improve inner city air quality.

- Living green roofs act as effective retainers and filters of storm water when it rains, helping to relieve pressure on urban sewage and storm water systems.

- They offer fire protection and extend the structural lifespan of roofs.

- Green roofs can lower noise pollution inside buildings, reducing sound from the outside by up to 40 to 50 decibels.

- They provide much needed green spaces, making cities more pleasant places to live and work.

- By absorbing light energy to grow, plants in green roofs can moderate a city’s microclimate, dampening the urban heat island effect in summer.

- Their installation and maintenance creates jobs for rooftop gardeners.

- City building roofs are increasingly popular areas to grow food locally and sustainably.

Last month, the French government enacted a new law that requires all new commercial buildings in the country to be covered, at least in part, by plants or solar panels. In 2009, Toronto adopted a by-law mandating green roofs for many new industrial, commercial, institutional and residential developments, and Basel, in Switzerland, already has extensive green roofs as a result of building regulations and financial incentives.

So how about it, city councils of Jozi, Cape Town and Durban? Why not take the lead in greening South Africa’s inner city roofs for everyone’s benefit?

- Andreas is a freelance writer with a PhD in geochemistry. Follow him on Twitter: @Andreas_Spath

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