Have we learnt anything from the Walkie Scorchie?
- 21st August 2015
- Posted by: wiredbarrister
- Category: Beechfield Consulting Engineers
Behind the headlines ridiculing the Walkie Talkie for its death ray and wind scoop effects are serious issues that should concern us all, says architect and urban climatologist Julie Futcher
The Walkie Talkie, aka 20 Fenchurch Street, has won the 2015 Carbuncle Cup as much for what it does to street life around its base as for its appearance.
The timing of the award is prescient. Today is the second anniversary of the event that gave it international notoriety. On September 2, 2013 the glazed and curved south façade of the 38-storey building managed to collect, reflect and focus solar energy on to a nearby street, raising surface temperature to over 90°C and damaging buildings and vehicles. This problem has since been addressed by adding a series of vertical fins to the face of the building.
But just as one issue was addressed another occurred. When the wind is off the River Thames the façade also acts as giant wind catcher, redirecting faster-moving, high-level winds to the ground.
Both these impacts are by-products of its height relative to the surrounding buildings and its curved form. And they are entirely (and easily) predictable outcomes.
Yet 20 Fenchurch Street is considered to be frugal in its energy consumption and has been given a Breeam Excellent rating. How do we reconcile this apparent contradiction?
The short answer is that a building’s sustainable credentials are assessed primarily on its energy efficiency, which is largely linked to the envelope fabric and internal management systems. This “fabric first” approach gives considerable scope to experiment with building form but, without consideration, can exert a strong influence on the surrounding micro-climate.
In cities, this means each building modifies the climate shared by other buildings and outdoor spaces. This mutual dependency is clearest where a new building radically changes the existing urban form and redistributes the shared natural resources (daylight, sunlight, wind), often to the detriment of its neighbours.
Unfortunately existing environmental assessments of buildings in cities do not account sufficiently for these effects. In this regard, 20 Fenchurch Street has lots of company.
The winner of the 2010 Carbuncle Cup was the Strata tower, another tall building with impressive environmental credentials. Its three embedded turbines have unimpeded access to the airflow over London and promised to deliver 8% of its electricity needs. However the turbines have rarely spun so its green standing is questionable.
Across the river in the City the Heron Tower has an impressive array of photovoltaic cells embedded in its south-facing façade. It has arranged its building services vertically so that potentially valuable adjacent office space is not used. However, it has no “right” to this passive energy resource. Once 100 Bishopsgate reaches its full height, much of the Heron will be in shadow during the hours of peak available solar energy, negating the tower’s renewable energy strategy.
Elsewhere, the planned development at Bishopsgate Goodsyard will create a set of tall buildings that will cast a shadow over the nearby Boundary Estate for much of the winter when heating costs are highest. Ironically this estate, which dates from the early 20th century, was designed with the climate in mind. The heights of buildings, the widths of streets and the layout allow access to sunshine and airflow. The current plan for the goodsyard emphasises its sustainability, but its form will make the Boundary Estate less sustainable.
These buildings all represent a type of architectural “exceptionalism” where their needs trump those of others.
In planning, the environmental impact of these buildings is assessed, although these methods have come under criticism for their limitations. Daylight, sunshine and wind assessments are usually done separately even though we experience the micro-climate holistically. Moreover, there is no requirement to account for the effect of one building on the energy management of another. In some cases the effect is acknowledged and purchased or the built form is modified. In the case of 20 Fenchurch Street the City of London Corporation used its powers to compulsorily purchase the “right to light” of neighbouring buildings that were cast into shadow.
More often than not the (un)desirable outcomes are treated as insignificant or even ignored. This is not to say that all impacts of tall buildings are negative. Shadowing the glazed envelope of an office building could reduce its cooling demand.
But until we establish a framework for evaluating the totality of the effects of these exceptional buildings on the wider urban setting, their environmental achievements will be suspect.
Some lessons have been learnt from the effects of 20 Fenchurch Street on the surrounding microclimate. The cost of fixing the south-facing façade to deal with solar reflection is likely to be a sufficient deterrent to stop similar design oversights in the future. However, the fact that basic solar geometry was not accounted for in the final construction is symptomatic of a building-centric perspective in a shared environment. Similarly, the negative wind effects have prompted changes to the way aerodynamic impacts from new construction are assessed.
On the other hand, these fixes do not address the underlying issue of reconciling the desirable qualities of an individual building with those of its urban neighbourhood.
Resolving potential conflicts will require a more holistic approach to assessing impacts and addressing responsibility. For example, should Bishopsgate Goodsyard compensate the Boundary Estate for increasing its heating costs?
The environmental management of cities is more complex than dealing with the particulars of an individual building or relying exclusively on renewables to reduce the impact of climate change and the growing energy crisis.
We need methodologies that can deal with the interactions that take place between buildings in our urban systems. To support this, a broader planning framework is required to guide urban development for form-driven microclimate effects.