Green roofs

Banana 'trees,' perfect for rooftop gardens. For trivial pursuit fanatics: Bananas are not actually trees. Their trunk is a pseudostem that dies once a bunch of bananas have been produced

Right now in major cities of the world enormously good things are happening in regards to built-up areas & green space. They too have growing populations. However, they have made decisions to make buildings more green, sustainable, people friendly as well as environmentally friendly. They are doing this because these buildings are going to be there for the next few decades & rather than continue to build unimaginative buildings that only house people, they are making the buildings also improve the environment while they are standing there.

Melbourne just announced the winner of a rooftop garden competition, the first of its kind in Australia as part of its Growing Up project. The winning rooftop garden was built on top of an old 10-storey office block & included a lightweight polystyrene hill covered in soil & planted with drought-tolerant plants & permeable glass paving to collect rainwater.

The Growing Up project says 20% of Melbourne city’s available space is wasted on unused rooftops. If we see an increase in the number of green roofs in Melbourne, we could see a reduction in the urban heat island effect of up to 2 degrees Celcius. We can also improve biodiversity, air quality & they really are a fantastic aesthetic addition to Melbourne’s space. http://www.abc.net.au/news/stories/2010/07/15/2954450.htm

An experimental rooftop garden at the University of Melbourne’s Burnley campus has shown an energy saving of up to 40% for cooling the building in summer. This is significant at times of high power prices & the serious issue of global warming.

Another benefit is better stormwater management as the rooftop garden catches & utilises as much as 80% of rainwater, meaning less water going down the drain, less stress on our often old & inadequate drains, less flooding of roads & footpaths & less stormwater running wasted into the sea.

Interestingly, the roof membrane lasts 2-3 times longer when there is a rooftop garden because the garden protects the roof from UV rays & temperature swings.

Green roofs combat the heat island effect dramatically without changing land use.  I’ve heard people query the relevance of the heat island effect saying they like heat, but when the surface of footpaths, outdoor cemented areas & roofs are 27-50 degrees hotter than the air, it becomes a major problem.  In built up urban areas, night time air temperatures can be as much as 12 degrees hotter due to trapped heat radiating out from the surfaces of buildings.  This makes for an uncomfortable time for those living close by as well as higher power bills, poor air quality from increased pollution levels because pollution gets trapped in the heat, as well as elevated greenhouse gases & ground level ozone.

If there is a heatwave, all these effects increase & can result in higher rates of respiratory problems such as asthma, heat stroke & heat-related deaths.

Although green roofs are not common in Australia, in other countries they are an established part of the infrastructure. For example, Copenhagen is about to adopt a policy that makes a green roof mandatory for all new buildings with roof slopes of less than 30%. http://inhabitat.com/2010/06/09/copenhagen-adopts-a-mandatory-green-roof-policy/

Chicago has a Green Roof Grant Program for a while & has over 200 green roofs, covering 232,257 sq metres (2.5 million sq ft). They have a very good picture of what a city could look like – http://www.artic.edu/webspaces/greeninitiatives/greenroofs/main.htm

Nice photos of green roofs in Chicago from 2006 -http://www.inhabitat.com/2006/08/01/chicago-green-roof-program/

90 second tour of a green roof -http://www.youtube.com/watch?v=8E278d5d0z0

5 minutes video of research on green roofs & their benefits -

http://www.youtube.com/watch?v=XxqdPOUoJ90&feature=related

Finally, from the benefits of Green Roofs IGRA World –

It is very difficult to find positive arguments for bare or gravelled roofs. Lower building costs for “Non-Green Roofs” in comparison to a Green Roof, are weak arguments considering it is only a short-term calculation. Long-term costs of maintenance & repairs of ‘naked roofs’ are much higher than that of Green Roofs. It has to be considered that roofs belong to the most strained parts of a building; if no precautions are taken & product qualities lack, problems arise quickly. http://www.igra-world.com/benefits/index.php

It would be wonderful if Marrickville Council adopted green roofs as a standard in their new Local Environment Plan, a draft of which is soon to be released for public comment. These types of roofs are likely to be commonplace in the future because built up urban areas are becoming very hot & costly in terms of power use. Businesses will want to save costs where ever they can. The initial outlay is going to be ultimately cost effective because of a 40% reduction in power costs & because a green roof is expected to last at least 20-30 years without maintenance.

Marrickville Council could build on their reputation as a Green Council by encouraging green roofs & green walls at all new major developments & set the standard for other councils to follow.  More on green walls in a future post.

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