Designing buildings to cope with extreme climate events: Part 1

As the global temperature continues to increase, so too does the frequency and intensity of the catastrophic climate events it causes.

In September last year, the Bahamas was hit by a Category 5 hurricane – the strongest the islands have ever endured. And worse is predicted: in February last year, a study part-funded by the National Oceanic and Atmospheric Administration and published in Nature, suggested that, in future, similar storms will strengthen faster in the Atlantic Ocean.

Large parts of the UK have battled floods over the past year. In November, the rivers Severn and Avon burst their banks, and the Sheffield Met Office weather station reported its wettest ever autumn.

It seems undeniable that climate change is ushering in a new world of extremes, with each posing a unique risk to different elements of the built environment. With that in mind, we take a closer look at precisely what those threats are and, perhaps more importantly, what can be done to mitigate their potentially disastrous effects.

Wind

Tall buildings are particularly vulnerable to extreme wind speeds, especially when it leads to a process called vortex shedding. This occurs when wind moves past a building, creating a fluctuating low-pressure area (vortex) behind it, causing the building to vibrate or sway. The taller and more uniform in shape the structure, the more damaging vortex shedding can be.

As cities construct taller and taller buildings in the face of rising urbanisation, innovative solutions to vortex shedding will become more pressing, especially as winds become stronger and more frequent. Research published in November last year, a report in the peer-reviewed journal Nature Climate Change, suggested that shifting global ocean circulation may have triggered a significant change in wind speeds over the past 10 years. Analysing data from 9,000 weather stations, researchers found that in the past decade wind speeds have unexpectedly increased.

Currently much of the focus on mitigating against this problem is on improving the aerodynamics of buildings, smoothing sharp edges to reduce the strength of the vortices.

Shanghai Tower, which stands at 128 storeys and 2,073ft (632m) in height, making it the second tallest building in the world, is a good example of how this works in practice. The tower is susceptible to sways of up to 5ft (1.5m) during the region’s regular typhoon conditions and has been designed with a twisting, smooth, triangular shape that has been found to reduce the force of typhoon-strength winds by nearly a quarter.

The tower is also equipped with a 1,200-tonne mass dampener – a computerised stabilisation system that counteracts the motion and slows the sway.

Another method used to minimise the areas where vortices can form is to taper the shape of the building as it rises. This is evident in the design of the world’s tallest building, Burj Khalifa in the United Arab Emirates. It rises from a flat base, with setbacks occurring in an upward spiralling pattern and the central core emerging at the top of the structure to form a spire.

However, with space at a premium, tapering isn’t always possible – or even desired – as demonstrated by New York City’s super-skinny 432 Park Avenue tower, which is a perfect square that reaches 1,398ft (426m) in height.

Rather than tapering the building or smoothing its corners, engineer WSP sought to reduce the likelihood of vortex shedding by omitting the glazing from the mechanical floors, which occur at 12-storey intervals all the way up the tower, allowing air to pass through the building.

But it isn’t just tall buildings that are affected: low-lying properties face their own challenges, particularly if they are located in hurricane-prone areas.

Having inspected the devastating impact that Hurricane Dorian had on properties in the Bahamas, Quantity Surveyor Ron Taylor MRICS says that work still needs to be done in some areas to implement and enforce building codes to better prepare for severe storms. Taylor says inadequately fixed hurricane straps, which play a big part in keeping the roof anchored, as well as the design and installation of hurricane windows and doors, were frequent problems.

While bad design clearly heightened the vulnerability of these properties, elsewhere innovative design is being used to reduce the risks associated with hurricanes.

Water

Not far from the Bahamas, in Miami, Koen Olthuis, from architectural firm Waterstudio, has designed a storm-resilient home in partnership with housing start-up Arkup. Built on water, the home is fixed with several stilts that enable it to move up and down with rising water levels during a storm, and withstand winds of up to 156 mph (251 kph). The first prototype was built last year.

“In an extreme situation, where there is a hurricane – and they’ve just tested it with Hurricane Dorian – the technology enables the house to move up 6m above the water, so it’s really like a growing house,” says Olthuis.

Olthuis’ firm has also been involved in the building of a sustainable floating neighbourhood, called Schoonschip, in Amsterdam. Schoonschip, which is still under development, will eventually have 46 homes built across 30 floating plots and be home to more than 100 residents.

The idea behind the community is that it makes better use of Amsterdam’s available space, while developing houses future-proofed against rising sea levels. So far, 26 homes have been built.

“In the project all the clients try to be as sustainable as possible and try to take as much from the natural energy around them as possible,” explains Olthuis. “So, many of the houses have systems in the water that can take heat out of the water during the winter or cold out during the summer.”

On this latter point, the heat is generated by water pumps, which extract warmth from the canal water. Tap water is then heated by sun boilers in warm-water pumps, while all the showers are equipped with installations that recycle the heat.

Elsewhere, green infrastructure is being used as a more environmentally friendly way of protecting against storm waves and coastline erosion.

One city that’s doing particularly well in that regard is Singapore, largely due to the state’s Landscaping for Urban Spaces and High-Rises (LUSH) programme, which places a requirement on developers to integrate green features into their building, the level of which must equal the size of land that was used for the development.

Far from merely improving the aesthetic of the building, foliage also boosts the drainage system, with the plants and substrate absorbing the water before releasing it naturally into the environment at a slower rate.

With these types of benefits in mind, Autodesk came up with a software solution to help designers and engineers incorporate green infrastructure into their building developments. The Green Stormwater Infrastructure (GSI) plug-in works alongside Autodesk’s InfraWorks infrastructure design software, which supports the building information modelling (BIM) process.

Floyd explains: “They [Designers and engineers] can choose and customise a variety of techniques – including green roofs, bioretention, harvesting, swales, permeable pavement, trees, infiltration and wetlands.

“GSI’s ability to provide real-time feedback on stormwater performance with each design change enables users to iterate quickly, compare alternatives, and improve their designs. Engineers, landscape architects and planners can use GSI as part of their early-phase planning and conceptual design process for new or existing development projects.”