Tuesday, August 01, 2006

HOW GREEN IS MY ROOF (AND MY PRINCIPLES) — try this database and see which countries are the leaders in this new “green” technology [1 ].

What is a Green Roof?

This is a building roof that is completely or partly covered with a growing medium (vegetation and soil) and uses a waterproofing membrane to isolate this garden from the rooms below. A roof with container plants is not usually considered to be a “green roof”. Sounds great except that plants used on a roof garden are not usually the type you can walk, but somehow the idea of lounging on the roof top soaking up a summer tan is unlikely to be financed by the perpetually cash-strapped university – but it can provide habitat for birds, insects etc.

So what are the advantages?

We know its going to cost more, so how do you justify, well here goes with the advertising…

  • Reduces storm water run off. this might not sound much, but with climate change and more extreme events that storm water discharge can be too much and get into the sewage and you are living in the proverbial cesspool [2 ]. I still cannot help thinking to collect the water in a conservancy tanks is cheaper and possibly more useful, f a drought were to come around. The vegetation filters pollutants, especially heavy metals and they get contained and not spread into the water system.
  • Reduce CO2 emissions, and there is more vegetation to take up the carbon.
  • Increase habitat for wildlife – possible this roof could be cat-proofed so the local birds can breed unmolested.
  • Increase roof life span (got this from Wikipedia) but it does not explain how.
  • Reduce heating cost during winter months (provides natural insulation so you do not lose so much heat) and promotes cooler interiors during the hot moths (evaporative losses and again the insulating factor). This has been demonstrated to be considerable in high northern latitudes [3 ], especially when situated far from the cooling effects of the sea and large water bodies (continental areas). Studies in Canada have suggested a 25 percent reduction cooling needs during summer and a 26 percent reduction in heating costs during winter
  • Creates open (amenity) space, this is probably not an issue on UWC campus.
  • If more buildings had Green Roofs in high density cities you would reduce the so called “Heat Island” effect [2 ]. One estimate put this at reduction in 16%.
  • And finally to grow useful plants– well the Egyptians use this to grow strawberries and other edibles – but then the roof has to be sort of flat or your abseiling skills need to be pretty good [4 ].

Who’s clever at building Green Roofs

Well a reconstruction of a Viking house along the Labrador coast of Canada has included a green roof – looks quite groovy too, but apparently the Native North Americans may have a clam to the first Green Roofs with their sod house [5 ] well European colonization put pay to that idea for a few centuries, with few eccentric Scandinavians maintaining the tradition in a low key way. Well the clever Swiss can claim one of the first big Green Roof developments back in 1914

Switzerland has one of Europe’s oldest green roofs, created in 1914 at the Moos lake water-treatment plant, Wallishofen, Zurich. Its filter-tanks have 30,000 square metres (320,000 ft²) of flat concrete roofs [3 ]. To keep the interior cool and prevent bacterial growth in the filtration beds, a drainage layer of gravel and a 15 cm (6 in) layer of soil was spread over the roofs, which had been waterproofed with asphalt. A meadow developed from seeds already present in the soil; it is now a haven for many plant species, some of which are now otherwise extinct in the district, most notably 6,000 Orchis morio (green-winged orchid).

In Germany it is estimated that 10 to 12 percent of roofs are already green and they are certainly the leaders in implementing the technology, whereas other than in a few cities (especially Chicago and Portland) the USA have a little way to go before fully accepting the idea. Nevertheless the Ford HQ has one of the largest, if not the largest greenroof area at a single installation. In the UK the University of Nottingham has a library with a Green Roof – so internationally we would be a bit Johnny come lately.


This all sounds politically correct but they are going to site this new high-tech in the dog-leg section of the Cape Flats Nature Reserve. The where-abouts of the new building has not actually been known to us in the BCB or EERU until quite recently (this June), and even now I am not sure exactly "where" in the dog leg it is to be sited, what I can say is that particular habitat is extremely rare (Sandplain Fynbos), as opposed to what the Cape Flat Reserve mostly represents which is Coastal Thicket which is fairly well represented by the existing Cape Town City reserve network and in any case Dune Thicket is both "less" sensitive and "less" unique. This situation is made more sensitive still, since the substrate of this site is acid and any building will introduce concrete and change the pH of the soil which has been shown to have impacts on acid-adapted plants. A alternative site (West of the dog leg) has already been wasted, it has easy vehicle access (East side of the Senate Building) making for easier construction and very likely easier connection to other services like sewerage etc. Since this site fronts onto the natural area along the North East boundary the "dog leg" part of the reserve would actually complement the building aesthetics, further if the long side of the building were parallel to natural vegetation you would maximize light, but minimize excess heat (North East is usually considered an optimal orientation for building in this part of the world, whereas a North West aspect long-side facing Modderdam Road is hotter in summer and colder in winter — making for more energy demands ). Further this site is closer to the Library and central University buildings than the dog-leg site- it is still next to the road so it can make a statement of sustainable design. Existing pedestrian access could be upgraded in front of the Gold Fields Centre) to connect to the rest of Campus. Search and Rescue has been suggested by the planners but is also not feasible, due to there being very little acid substrate areas to move the "rescued" plants into.

Possibly the most ironic aspect of this is we are one of the few Univeristy that has mission statement directly relating to the environment

"Help conserve and explore the environmental and cultural resources of the southern African region, and to encourage a wide awareness of them in the community"

The University is apparently not oblige to undertake an Environmental Impact Assessment and is not intending to do one either! This is not the first time that a University building has encroached on what is essentially the reserve area — the new School of Government was its first grab! I will keep you informed.

[1] The Greenroof Project Database [Internet]., undated [cited 2006 Jul 28]. Available from

[5] May your Roof be green. [Internet]. Al-Ahram Weekly On-Line: Environment; 2005 Jun 28, [cited 2006 Jul 28]. Available from:

Leave a Reply