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1 Blight Street Sydney | Commercial architecture

Using natural ventilation to reduce the spread of airborne viruses

Pandemic proofing city buildings through mixed-mode and natural ventilation

The architecture profession is questioning how COVID-19 will shape future cities and their buildings.

While we should expect new technologies that will make buildings more resilient, increasing our emphasis on design features that we already know to be effective in preventing the spread of communicable diseases may be among our most powerful tools to safeguard urban populations faced with future pandemics.

Communicable diseases account for several million global deaths annually, even in pandemic-free years. Many are transmitted in indoor environments through either close exposure to a carrier, or through micro droplets that can linger in poorly circulated air for up to several hours. Outbreaks of COVID-19 – including well documented, catastrophic outbreaks on cruise ships – reveal how quickly airborne viruses can take hold in sealed indoor environments, particularly those containing ventilation systems that recirculate air between spaces.

Research has shown that natural or mixed-mode ventilation markedly reduces the spread of airborne viruses in indoor spaces. One 2007 study of Peruvian hospital wards modelled infection rates of tuberculosis across mechanically ventilated rooms built between 1970–1990, mechanically ventilated rooms built post-2000, and naturally ventilated rooms, many in older buildings with high ceilings and large operable windows. The results suggested the post-2000 rooms were only somewhat more effective in reducing the spread of infection than the 1970–1990 rooms, with 33 percent of patients infected in the newer rooms versus 39 percent in the older. However, in the naturally ventilated rooms infection rates dropped to 11 percent.

In Australia, our practice has been a leader in designing contemporary towers comprising natural or mixed-mode ventilation systems – a feature that not only improves air flow and quality but significantly reduces a building’s carbon footprint.

For example, highly-awarded Sydney office tower, 1 Bligh Street – which we co-designed with Ingenhoven Architects and was completed in 2011 – was Australia’s first high-rise office building with a naturally ventilated atrium and balconies on every floor. Operable windows through the full height of the atrium allow fresh air to circulate, a feature that decreases the risk of infectious doses of micro droplets lingering.

As Sydney workers return to their offices, a design scheme conceived more than a decade ago to create a green building with a healthy and permeable ground plane will now help safeguard 1 Bligh Street’s COVID-wary occupants as they come and go. Multiple entry and exit points into the building and a generous ground plane will reduce peak hour congestion. People can safely enter and gather in the lobby area while they queue for the lifts, which will now accommodate fewer people. Staff can take breaks on the building’s atrium balconies and rooftop terrace, which are naturally ventilated and exposed to sunlight – another means of reducing the infection rates of airborne viruses.

1 Bligh Street uses natural ventilation within the atrium and on balconies on every floor.

Since 1 Bligh Street, we have continued to design advanced natural and mixed-mode ventilation systems across a diverse range of projects. Some of these are new builds like 1 Bligh Street, while others were created in the context of existing buildings. For instance, when we designed the Qantas Headquarters in Sydney, we were tasked with transforming an outdated 1980s office campus into a modern and sustainable workplace. A major part of this project was designing an efficient, mixed mode ventilated atrium that connects the campus spaces and innovatively uses spill-air drawn from adjacent office floor plates to regulate temperatures throughout the seasons.

Natural and mixed-mode ventilation systems are just one example of how buildings can protect occupants from airborne viruses. Some buildings are sealed and mechanically ventilated for practical and climatic reasons. In these cases, design features that are already common in hospitals such as optimal humidity control systems and air cleaning light filters including UV light filters may become increasingly standard in city high-rises.

Scientists warn us that, in a world with a growing and evermore global population, the instance of pandemics will rise. Many cities are adjusting to COVID-19 – imposing social distancing rules, sectioning off roads to widen footpaths and bike lanes, taking citizens’ temperatures before they board public transport. What remains uncertain is what the enduring impact of COVID-19 will be; how will cities and their buildings change so that when the next pandemic strikes, we are better prepared?

We don’t have to look far back to find examples of global events comparable to the COVID-19 pandemic that changed the course of architecture and design. In the wake of the cholera pandemic of the 19th century, countries constructed more hygienic sewer systems and introduced new zoning laws to prevent overcrowding. Almost a century later – as the world endured two world wars, the Spanish Flu pandemic and the Great Depression – the minimalist design principles of modernist architecture began taking seed. The desolation of the first half of the 20th century saw the great mid-century architects aspire to create pared back, light-filled buildings – blank canvases for the ideas that would form a better future.

Today, we are more informed and better equipped than ever to design spaces that protect people from the overlapping challenges arising from climate change and globalisation, including rising urban populations, extreme weather and natural disasters, and future pandemics on par with COVID-19.

If developers and architects rise to these looming challenges, one positive outcome will be to fast track the next generation of sustainable, naturally ventilated towers, through which clean air flows and people can breathe easy.

This article first appeared here on Architecture & Design.


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