As we have seen with sustainable urban drainage (section 2.8), definitions and policy are important. Voluntary inclusion of green infrastructure elements in high-profile landmark developments can be visually stunning and inspire other developers and architects, but it does not necessarily make it easier to ensure that such features are included in the more mundane, run-of-the-mill building projects. I lived in Cologne, Germany, for six months over the winter of 1985 to 1986 and was astounded at the extensive use of UPVC (PVCu) windows with double-glazing; back home in Southampton, England, it was something of a rarity with most houses being single-glazed. Now, in the UK, all new builds have to be double-glazed, and most replacements as well, on energy eciency grounds (FENSA, undated). If doubleglazing had been left to purely voluntary action, it is likely that many buildings now with double-glazing would have remained single-glazed.