New heights in Green Building 


In many people’s minds, green buildings are simply associated with energy conservation and green star ratings. A fascinating talk was, however, given at the Green Building Conference in Cape Town on the Bosco Verticale (Vertical Forest), by Maria Pastore of Stefano Bueri Architects.

These two residential towers in the centre of Milan, Italy are literally green. They are 110m and 76m high but what makes them really interesting is that the two buildings host 65 million Euros of tree, shrubs and plants in what could literally be described as a vertical forest. Over 10 000m2 including around 800 trees of between 3m and 9m, 4500 bushes and over 15000 plants were planted in this metropolitan reforestation project. It is argued that this biophilic design can result in significant energy savings and wellbeing of the inhabitants, besides the obvious aesthetic advantages of a more natural living and working environment and protection from noise pollution from the streets.

The interesting aspect of this living façade is that exfoliated Perlite was used in the growing media to ensure that the structure could bear the load imposed by the plants. To put this in perspective, conventional, fully watered soil weighs as much as 1900-2200 kg/cubic meter without the weight of plants or trees. This is close to the full weight of concrete. When this is multiplied by the number of planters and plants on a building such as this, the additional weight on the structure can be massive. In contrast, fully watered perlite and peat moss/compost growing mixes weigh about 550-600 kg/cubic meter and the high quality 100% horticultural grade perlite we supply weighs as little as 80-100kg/cubic metre. This tremendous weight saving using perlite can provide architects, developers, designers and nurserymen with a host of additional options including more extensive plantings, larger shrubs and trees and reduced design loadings on buildings.

It is for these very same reasons that Perlite is used highly successfully as an aggregate replacement in lightweight concrete with typical cured densities of around 500kg/ cubic metre.

The advantages of using perlite are not limited to weight savings only. Perlite is an inorganic mineral of volcanic origin and it therefore does not rot or deteriorate over time. Perlite will also retain three to four times its weight in water and water-soluble nutrients without becoming soggy. This results in healthier plants and trees with better soil aeration while requiring far less attention and less water. When used in concrete it also assists in hydrating cement. In addition, it offers the advantages of being pH neutral, non-toxic and sterile, having been exfoliated at nearly 1300 deg C.

I found an interesting video on this project.