The “Yes” Versus “No”for Sustainable Tall Buildings
In the “No” side, it is quite simply a myth that high-rise means high density. Based on statistics, Manhattan with its iconic valley of skyscrapers has a density ratio of about 27,000 people per km2 making it by far New York’s densest borough.
Nonetheless, the centres of Paris and Barcelona, with their tight, compact grids of mid-rise apartment blocks and a complete absence of high-rises, generally offer density ratios of 26,000/km2 and up to 36,000/km2, respectively. It is difficult therefore to cite growing population as a justification for skyscrapers. In addition, the negative view poll by Lynne Sullivan, Environmental Design Studio Sustainable by Design sees that there are social concerns simply “Sustainable for whom?” She cites the increasing expansion of towers across London as symbols of a corrosive social rupture. “These towers are often privatised vertical cities that essentially operate as safety deposit boxes for foreign investment. Towers can’t replicate the vibrancy of public realm or the livability of streets. They have more negatives than positives and there are better density models” (http://www.bdonline.co.uk/can-tall- buildings-ever-be-sustainable?/5074042.article; http://www.building.co.uk/can- tall-buildings-ever-be-sustainable?/5074035.article).
Moreover, the most negative arguments against the sustainability credentials of tall buildings are not social or demographic, but environmental. Various studies, including those by building physics consultancy Inkling, have identified a long list of detrimental environmental effects caused by tall buildings. In terms of energy, the increased use of glass in skyscrapers and the high concentration of inhabitants ensure that towers often consume extremely high heating/cooling loads, which will make them highly susceptible to overheating. Combating this normally requires a huge amount of mechanical ventilation which, coupled with other mechanical and motorised apparatus-like lifts and service shafts which require ever greater amounts of energy, hence more CO2 emissions. Glass surfaces also ensure increased conduction heat loss.
From the microclimate viewpoint, tall buildings also cause wind speed to notoriously accelerate, in particular at their bases, which in turn, makes the surrounding areas suffer. Not only do these wind speeds make natural cross-ventilation within the building difficult, but they largely prohibit the use of open balconies at high levels, another aspect which many cite as evidence of tall buildings’ innate incompatibility with the residential typology. The negative environmental impact of high- rise buildings can extend beyond the building’s boundary line. Sets of towers can also create dark zones where concentrations of still air and pollution can be found when wind speed is low. As far as the urban heat island effect is concerned, tall buildings may increase the damage to the environment in warmer climates. But in terms of daylight and solar gain, towers can cast greater portions of the street level in shadow, resulting in a loss of daylight and solar gain for surrounding properties. This in turn could result in a greater reliance on artificial light which requires the use of additional energy. In old cities where urban sites are surrounded by high blocks, the use of renewable sources on tall buildings can be difficult due to the blocked sunlight for solar panels and once again forcing greater reliance on carbon energy
However, if the urban site is surrounded by low-rises then this is not a negative point. Simon Sturgis (Carbon Profilers Sturgis Associates) added that “the more you go higher the more inefficient the building becomes in terms of the net area measured against carbon emissions from operation, construction, and maintenance”. He added that “the life expectancy of glazed cladding systems is only 40-50 years before replacement is required”. In comparison, Sturgis recommended key suggestions that may make tall buildings more efficient and therefore more sustainable. “Tall buildings should have much greater resilience and last longer to justify their huge cost. Materials should also be fully recyclable and towers should have to provide a detailed whole-life carbon analysis and operate within an embodied carbon threshold” (http:// www.bdonline.co.uk/can-tall-buildings-ever-be-sustainable7/5074042.article; http:// www.building.co.uk/can-tall-buildings-ever-be-sustainable7/5074035.article). Recent tall buildings have considered such points however.
In contrast, the “Yes” poll, have many who are sharing enthusiastic support for sustainable tall buildings and purging Sturgis’s argument. This is mainly seen in the Gherkin’s double-skin facade and its swerving internal atrium (chimneys) assisted to render the building a pioneer of environmental high-rise design for its time (Fig. 9.12). Also, the 121-storey Gensler’s Shanghai Tower (632 m) claims to be the world’s first eco-skyscraper includes features such as its wind-minimising tapering form and one-third of its interior space being allocated to public gardens have earned the building a coveted LEED Gold certification and helped it reduce its carbon footprint by an impressive 34,000 metric tonnes a year in comparison with an equivalent building of the same size (Fig. 9.13). The 20-storey, 80 m-high RHW.2 tower in Vienna (Fig. 9.14) is considered the world’s first Passivhaus office tower that is fully clad in glass, the signature skyscraper envelope material synonymous with environmental waste and efficiency. Three key measures made the RHW.2 to obtain the Passivhaus status. This innovative tall building uses 80 % less heating and cooling energy than an equivalent tower. This was obtained through the incorporation of a unique well-insulated double-skin facade which provides high air tightness and thermal efficiency levels. Also daylight was allowed to penetrate deeply into the interior through the floor plate’s slender surface (18 m deep), thus reducing reliance on artificial lighting (http://www.bdonline.co.uk/can-tall-buildings-ever-besustain- able?/5074042.article; http://www.building.co.uk/can-tall-buildings-ever-be--sus- tainable?/5074035.article). In addition, the Shard tower in London (Fig. 9.15) has a barrage of sustainability features which have enabled it to use 30 % less energy than a conventionally designed skyscraper of the same height. In this tall tower, a combined heat and power (CHP) unit which has a ventilated triple-skin facade was incorporated. This unit consists of low-ion glazing with low emissivity coating and an integrated energy system which maximises energy efficiency to balance energy demand in accordance with requirements at various times of the day. Lastly, the tower is fitted with highly advanced mechanical systems (automatic or manually operated shading system installed within the facade cavity and multiple occupancy
Fig. 9.14 Passivhaus RHW.2 Office Tower, Vienna, Austria. Image source: http:// urbangreencouncil.org/ content/events/ passive-House-office- tower-
Fig. 9.15 The Shard Tower, London, UK. Image source: https://upload. wikimedia.org/wikipedia/ commons/c/ca/ London_01_2013_the_ Shard_London_ Bridge_5205.JPG and luminosity sensors to regulate energy use accordingly). Extra measures include photovoltaics, ecologically certified construction materials, openable inner-skin windows for natural ventilation, and a CHP that generates 60 % of the tower’s power and 40 % of its heating.