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Have you ever wondered how much energy it takes to produce a new car? Or, for that matter, a new building? No? Well you should, because the energy 鈥� and related CO2 emissions 鈥� embodied in a building鈥檚 materials and components is a significant proportion of the energy used during its lifetime. Energy in use, not embodied energy, has been the sole measure of energy efficiency for some time. Take cars: miles per gallon is a well recognised measure of fuel efficiency, and green ratings based on CO2 per kilometre travelled are becoming increasingly popular. In these terms, we would expect the new style of green vehicles (Toyota Prius et al) to outperform their larger, more fuel-hungry ancestors, the likes of 4x4s so derided by environmentalists, yet so loved by Chelsea farmers. But lift the bonnet 鈥� or, more specifically, look behind the new technology 鈥� and a rather different picture emerges.

Last year, a report on automotive energy by CNW Research, Dust to Dust, was published in the US. It compared the green attributes of cars, including design, manufacturing, operation and, most importantly, disposal and recycling over the complete product lifecycle. The report, picked up on by What Car?, covered 96 cars sold in the UK. Of those, the Honda Civic Hybrid finished 73rd on the list and the Toyota Prius 74th 鈥� even though they have some of the lowest CO2 emissions of any car and are usually regarded as the most environmentally friendly. More surprisingly, so-called gas guzzlers such as the Range Rover Sport finished higher up the list.

What goes in鈥�

It's all down to the materials involved and the energy and resources used to process and produce them. The car rated greenest was the Jeep Wrangler because of its long life, simplicity of design and manufacture and ease of recycling keymaterials at the end of its life. To take a more extreme example, the relatively conventional steels used in a Hummer H2 4x4 have a lower embodied energy value than the higher-tech steels and alloys in a Toyota Prius.

The conventional steel is also easier to recycle. And of course the Hummer is more than twice the kerb weight of a Toyota Prius. In general, hybrid vehicles do not come out terribly well from this analysis, primarily because of the manufacture, replacement and disposal of high-energy-use items including batteries and aluminium alloy electric motors. As the report authors' note: 鈥淲e believe that basing purchase decisions solely on fuel economy or vehicle size does not get to the heart of energy usage.鈥� Quite. And it's the same sort of thing with buildings. Over the past six months at Davis Langdon, my colleagues Simon Rawlinson and David Weight have been taking a similar look at the embodied energy and associated CO2 emissions of different building types. We feel this is an important, yet currently missing, element in understanding the total energy and carbon associated with buildings over their lifetime. Indeed, with the current emphasis on the efficiency of energy in use 鈥� and from next year energy performance certificates for non-domestic buildings will only reinforce this 鈥� there is a need for clients and building designers interested in the real carbon footprint of their buildings to take careful account of embodied energy and associated CO2.

That is why we have developed a carbon rating that can identify which building elements carry the highest carbon costs and which can be most easily mitigated. Although our findings for buildings are not so dramatic as for cars, they help point the way towards more energy- and carbon-efficient buildings.

Our early assessments suggest that embodied energy and associated CO2 equates to between eight and 15 years of operational energy. However, for new construction built to higher energy standards, about half the operational energy is not building-related but is associated with equipment and appliances such as computers and peripherals. In this case, embodied energy and associated CO2 equates to between 15 and 30 years of the building-related operational energy.

This is highly significant, particularly for buildings with a high occupancy turnover. Given their high rates of churn and refurbishment (the latter usually involving the replacement of energy-intensive partitioning and plant), it is quite possible for the embodied energy and associated CO2 of these buildings to exceed the operational energy over the its entire lifecycle.

There are lessons here for policy makers and regulators, who really need to get to grips with the lifecycle energy and carbon associated with buildings 鈥� and not just in use. Indeed, the current pre-occupation with renewable technologies for buildings 鈥� many of which, such as photovoltaic cells in buildings, are highly energy/carbon-intensive relative to their marginal contribution 鈥� is even less compelling when looked at in lifecycle terms.

Shifting the balance

From next month we will be introducing our carbon rating on many of the projects in which we are engaged, to help assess the balance between embodied carbon and carbon emitted during the building's operational lifecycle. It will also help clients and designers better understand the mitigation and reduction options open to them. We believe it is a vitally important piece of the sustainability jigsaw that has until now been missing.

Just as the data on cars should not be interpreted as a charter for the 鈥渂igger is better鈥� brigade, the way in which we compare buildings on the basis of their carbon rating needs careful thought. We have been considering banded rates on similar lines to those used to rate electrical appliances, but this could be unfair to certain designs. Towers, for example, will have a much higher proportion of structural steel or concrete than lower-rise buildings of equivalent area. There are also implications for lifts and other services.

The use of simple targets such as those used for cars 鈥� tonnes of CO2 per square metre floor area, for example 鈥� could be misleading. Instead, we are looking at ways of neutralising the effect of shape and other parameters, concentrating on the materials used and the benefits of mitigation measures.

Clients and designers are finding increasingly stringent regulation 鈥� including obligations for the adoption of renewable technologies 鈥� rather limiting. Our view is that significant reductions can be made to embodied energy and associated CO2, and thereby the real energy and carbon footprint of buildings, without compromising quality or the bottom line.