All discounting techniques require an assumption to be made about the lifespan of thebuilding under consideration. Traditionally, a 60-year life has been taken for analysessuch as those discussed above. The points made earlier with respect to notions of economiclife and obsolescence must, however, be borne in mind. One retail chain, forexample, takes an economic life to be 11 years, because it is assumed that at the end ofthis period the market will have either grown or disappeared, thus requiring eitherthe disposal or replacement of the building. This is becoming increasingly true of manymodern industrial buildings.The notion of the disposable building has become more readily accepted thanhitherto and investment decisions have been adjusted accordingly. In such a scenarioit is reasonable to expect this requirement to be an important aspect of user requirements,which should be clearly identified during the collection of the brief, andresponded to accordingly. Current sustainability debates, however, challenge thesepurely economic-based decisions and increasing environmental pressures will force amore holistic analysis of building life.