In the pursuit of energy conservation we must not forget the Vitruvian principles of commodity, firmness and delight. In this context, we read comfort for commodity; and the second underlying theme of these guidelines is that comfort should not be compromised, but in many cases improved. The pursuit of comfort is a basic drive in human behaviour, evolved for the purpose of survival (Figure 3.1), and is not just a sign of wimpishness! If the occupants of a building are subjected to discomfort for substantial periods no amount of architectural delight will compensate, nor will reduced energy bills.