Although they can be hard to pin down, any measures of CO2 emissions are useful.
The AJ has started to add CO2 emissions figures for each building study. We must all support this move. Initially, the figures will be difficult to compare and bare little relationship to reality, but even if they represent the most wild-eyed optimistic aspirations of the designers, they will be data to use for a wide statistical analysis in the future. Then the projections can be compared with actual measured figures. I advocate the collection and publication of any data, because the randomness of the results is useful in itself.
The energy use of buildings has been measured for many years, and the figures show very wide variations for apparently identical buildings. I once tried to analyse three years of energy bills for 1,000 flats. According to speculative calculations, a flat with no roof or gable walls would have half the energy use of a flat with roof and a gable wall. But my figures showed that there was no difference between these two types of flat because the variation caused by other factors outweighed the difference in construction.
The energy/carbon figures which are currently being calculated are skewed to the low side. The parameters which are entered into the computer databases include very little data on the users of the buildings or the skill of the maintenance team. Even things like errors in the control algorithms, or leaks in the ventilation ductwork cannot be taken into account. However, any calculations that are made thoroughly and purport to include all the energy exchanges of a building are worth consideration. It is not good enough to exclude those energy exchanges which are not controlled by the building designers. The total carbon footprint of a building is the important issue.
Max Fordham is founder of Max Fordham Consulting Engineers