The great office meltdown has begun

Remember the summer? those scorching August days when the thermometer appeared to be stuck above 30°C? When drinking water had to be rushed to site for workers sweltering on BAA's Terminal 5 project? And when temperatures at Gravesend in Kent smashed the record for the hottest day ever recorded in Britain – a very sweaty 38.1°C.

For developers and designers alike, this summer's extremes have come as a wake-up call. Specifically, they have prompted worries about the ability of existing office buildings to cope with the impact of global warming. Experts are now questioning current strategies for low-energy building design, and there are concerns about the appropriateness of the government's commitment to timber frame, modular and other factory-made lightweight construction systems.

Climate change is happening. In Review of the Potential Effects of Climate Change in the United Kingdom, published in 1996, the then Department of the Environment (now DEFRA) predicted that the mean summer temperature in the UK would increase by 2°C from 1990 to 2050.

While 2°C may not sound like a calamitous increase, it is important to remember that as an average value, the extremes that contribute to this rise are likely to be far in excess of any summertime temperature experienced to date. Already, the norms are shifting steadily upwards. "The number of hours when the temperature tops 25°C is growing year on year," warns Mark Way, head of research at architect RMJM.

This summer, many commercial buildings struggled to provide a comfortable working environment. Nick Cullen, a climate change specialist at consultant Hoare Lea, says most commercial buildings in the UK do not have air-conditioning, and that global warming will make it impossible to work in them by the year 2030. "Seventy per cent of all business premises are naturally ventilated: by 2030 they will become unusable in summer," he says.

The obvious solution to an overheated building is to fit a cooling system. "As climate change becomes more apparent over the next 50 years, existing naturally cooled buildings will increasingly need supplementary cooling," Cullen says. However, many buildings do not have space for air-conditioning plant or the service risers to house the labyrinth of pipe and ductwork essential to such systems. "Such buildings will not have a future," warns Cullen.

It is not just naturally ventilated buildings whose future is now being called into question; many air-conditioned buildings will also struggle to function as temperatures rise. Most cooling systems have been designed to "historical" weather data, which does not take into account climate global warming. "Climate change means we can no longer rely on that historical record, and we must seek to predict weather patterns," says Cullen.

Climate change is the death of lightweight construction

Architect Bill Dunster

Global warming will force architects and engineers to fundamentally rethink low energy building design. In a foretaste of summers to come, night-time air temperatures remained uncharacteristically high this summer. However, many low energy buildings rely on cooler night-time temperatures for their climate control. This is achieved through the use of heavyweight construction elements such as exposed concrete walls and floors. Concrete has a high thermal mass, which means it can absorb heat during the day, keeping the interior cool. At night, when the air is cooler, this heat is released from the building. But warmer nights will limit the amount of heat released from these heavyweight construction elements.

As a result, buildings that were designed to use night-cooling will fail to perform as intended, which means that naturally ventilated offices will become increasingly uncomfortable places to work. "Current passive design strategies of relying on diurnal temperature swings may become ineffective as climate change causes prolonged periods of excessive temperature," says Cullen. Geoff Levermore, professor of the built environment at the University of Manchester Institute of Science and Technology agrees with Cullen: "If you have hot days and hot nights, you are not going to get much cooling from the air," he says.

It is not just buildings with night-time cooling strategies that rely on thermal mass to keep temperatures within acceptable levels during the day. Many homes and offices use a heavyweight structure to maintain thermal stability.

However, most forms of off-site construction, such as timber frame and modular construction, do not use materials with a high thermal mass. Experts are warning that climate change will call into question the government's drive for increased use of standardisation and off-site manufacture in the construction industry. "If you are looking at buildings designed for the long term, then lightweight construction is going to be very susceptible to climate change," says Gavin Davies, an environmental engineer at consultant Arup.

Low-energy architect Bill Dunster agrees: "Climate change is the death of lightweight construction. It has not got a future in a country that will get increasingly uncomfortable in summer," he says. "You don't tend to find Mediterranean countries using lightweight construction."

With a lifespan of 30 years or more, buildings put up today need to be designed and constructed to cope with summertime temperatures far in excess of those experienced this year. Rather than rely solely on the use of outside air to keep buildings cool, the low-energy office of the future is likely to combine natural ventilation with some form of cooling – what engineers term a mixed-mode system. When it becomes too hot to cool the building using outside air, the occupants close the windows and switch on the air-conditioning.

For the design engineers, the challenge then becomes one of providing this additional cooling in an environment-friendly manner. One solution is to use cold water from deep underground instead of electricity-guzzling air-conditioning units. Consultant Arup used groundwater to keep London mayor Ken Livingstone cool in City Hall.