“Men build because they have need for specific kinds of enclosed space, and the appearance of the building they put up is very much a matter of taste” (Goldthwaite, 1980, p. 67). No doubt, the provision of an “enclosed space”, more precisely the provision of shelter, is the primary function of buildings and building. Hence the central concept of any building economics has to be the notion of shelter, by which we mean an enclosed space that maintains a favourable environment for some more or less specific process. Demand for shelter arises, on one hand, from the need to protect a process from natural disturbances, and on the other from the need to protect it from interference by other people. No demand for shelter is absolute. What is sought is not absence of any exchange with the outside world, but rather some specific amount of control over the environment of a process, i.e. some control over the inflows and outflows affecting a given process. After all, such things as hides, membranes as well as houses, tents etc. are not designed to hermetically insulate the process taking place within their confines (it is doubtful whether any meaningful process could unfold in a perfectly sheltered environment), but merely to keep out disruptive influences. After an initial euphoria for ever more perfect insulation after the first oil crisis, architects quickly learned that excessive insulation may well save a lot of energy but may also decrease amenity. Moreover, since the crucial thing is the favourable environment of a process it is useful to think of shelter in broader terms than in terms of material structure. In order to provide the proper environment the material structure will usually require such things as heating, cooling, ventilation, humidification, internal transportation and communication and other kinds of “catalysts”. To get a clearer understanding of what building economics is, it is useful to think of shelter as “buildings-in-operation”. This seems reasonable despite the fact that, in the market, shelter comes only in such discrete and separate items as service of a building without utilities (rental market), built buildings cum land (stock market), land (stock), land rental (service), construction services (service), utilities (service) so that production of the service of the building-in-operation is really achieved by the occupant who combines the various items.