SUSTAINABILITY

  Targets for sustainability have been set by the Royal Commission for Pollution. The targets are more strict than the current Kyoto agreements and they need to be. The proportion of the world population who have access to the benefits of industrialisation must rise if the population of the world is to stabilise at about 10 billion people. We should not be encouraging a new building type if it is inherently more inefficient in its carbon emissions than other competing building types. Buildings where people work need good light. Electric light is responsible for nearly half the carbon emissions of an office building. As the thermal properties of buildings are improved, using efficient glazing, CHP, etc, The need to reduce reliance on electricity for lighting must also be implemented. Natural lighting is the best use for solar energy. The energy content of natural light is given by the relationship 100 lumens per watt. It takes between 30 watts and 3 watts of carbon emission to produce 100 lumens of light. So natural light is one of the most efficient ways of using solar energy to replace carbon emissions. On an overcast day the sky produces 5,000 lumens per square meter of which 2,000 lumens reaches a square meter of vertical window. There is a limit to the depth into a building which can be reached by light from a window. The limit is one or two times the height to the window head. Tall buildings need to be served by lifts, escape stairs, and other services. The area of these essential, but not productive parts of the building has to be minimised. For tall buildings the depth from the window to the back of the office is maximised so that the ratio of useable to total area is economically feasible. For the Nat West Tower the useable to total ratio is less than 50 per cent and the depth of the offices is around 7 metres. At Canary Wharf the depth is around 14 metres, the building is more efficient in terms of net to gross area, but he 14 metre deep offices rely on electric lighting. Any modern building will have to show compliance with current building regulations. The building regulations as currently tabled are an interim stage in reaching the eventual targets for sustainability and we should not be opening the doors to a building type, which is bound to need electricity for lighting.

  Tall buildings are exposed to strong wind forces. It is generally accepted that the buildings need sealed envelopes and mechanical ventilation and air conditioning. Mechanical ventilation and air conditioning do increase the Carbon emissions of buildings. Again we should not be encouraging buildings which will increase emissions.

  The increase in town density should reduce carbon emissions caused by transport. One of the important research results of the 60s was that a density of around 500 p/ha could easily be achieved by low-rise buildings. The current planning policy of limiting housing density to 100 p/ha needs to be revised, but it is not necessary to aim for say 5,000 p/ha as in Hong Kong, nor is it necessary to build extravagant showy buildings now.

SAFETY

  The requirements for phased means of escape need to re-examined while we sort out what can be done (if anything) to prevent collapse of buildings which may obtain more people than can escape in a short time.

  Max Fordham MA, FREng, FCIBSE, Hon FRIBA, Visiting Professor Dept Civil Engineering & Architecture, University of Bath.