Anyone still prepared to dismiss this kind of architecture as cranky or fringe or provincial should turn their eyes to Westminster, where the new and very expensive Parliament building by Sir Michael Hopkins is taking shape and will open in a year's time. It is designed to last 120 years, twice as long as most new buildings - and Hopkins himself confidently gives it 200. Its roofscape of tall chimneys tells you that it intends to see out its term without much recourse to artificial cooling: like the Contact Theatre, but in a rather more sober suit of clothes, it will be naturally ventilated. And strangely enough, one of the reasons it looks the way it does is because it is a neighbour to a pair of fine and exuberant tall-chimneyed Arts and Crafts buildings alongside by Richard Norman Shaw - together comprising the former Scotland Yard, built in 1890 and 1906.

Norman Shaw's chimneys were, for all their finery, merely smoke vents. Hopkins's versions on the new building alongside will remove stale air from their tops, recycle the heat (or coolness, depending on the season) and transfer it to fresh air drawn in at their bases. You can trace the course of the air-channels from the chimneys, across the sloping roof, and down the facades to individual offices. What it is saying, in a bigger though less strident way than Short's Contact Theatre, is that "greenness" - something that was in the brief for the Parliament building from the start ten years ago - can play an important part in determining the external appearance of a building. Only Richard Rogers really tried to do the same thing with air-conditioning ducts (consider the 1976 Pompidou Centre in Paris), and even he gave that up after a while.

There is an office block in Hertfordshire by architects Feilden Clegg, with tall stainless steel chimneys for the same purpose of natural ventilation. There is a new university college in Durham by James Burland of Arup Associates, where a village of student housing will cluster around tall "wind towers" which save energy. Richard (now Lord) Rogers has designed the new Welsh Assembly in Cardiff with prominent vents sprouting over the hot-air generator of the debating chamber. The famous glass dome of Lord (Norman) Foster’s transformed Reichstag in Berlin contains a spectacular vertical air-trumpet doing the same thing, as will the Darth Vaderish helmet of his proposed Greater London Assembly building. It seems architects have latched onto something they can have fun with: the old idea of form following function is re-emerging in a new guise.

Most of Hopkins' new buildings now work this way - often with glazed stairtowers acting as solar-powered chimneys. As Hopkins puts it: "It stops us being whimsical. It gives us something to hang onto and to develop." By "whimsy", Hopkins means architectural forms that are purely decorative, with no functional justification. That, of course, is a definition of post-modernism. But something has changed. Chimneys did not easily fit with the flat-roofed, horizontal aesthetic of the post-war years, which coincided with the rise of central heating and airconditioning. Now, as in earlier times, there is a ready-made justification to design something vertical. But as Hopkins remarks, "In the 1950s and 1960s, maybe we didn't want that."