Building 16, a new addition to the Design Council's milennial list, is a model for energy efficient office buildings of the future. Utilising natural energy sources, it could prove to be an architectural milestone - but only time will tell.
Building 16 is as energy-efficient an office building as Britain can offer, or so the Design Council hopes. They have put it on their millennial list, but in truth they don't really know whether it works or not. By the time the millennium comes, we will know. Still, it is a three-storeyed building, to be found at the Building Research Establishment at Watford, designed by the Bath practice of Fielden & Clegg to provide "a 30 per cent better energy performance than previous buildings".

It is supposed to be state-of-the-art, and it probably is, but it must be said that the story of its construction had its unstate-of-the-art moments. There was a major glitch at the start: imperial-sized bricks and metric floor plans - and this for BRE, the UK's leading source of independent advice and information on building performance, construction and fire safety.

The bricks were imperial measure because the intention was that it would be built from old bricks recycled - 20,000 of them from the demolished building on the site. But the Portland cement that bonded them meant that nobody could separate them. A crusher had to pulverise them on site. Other salvaged bricks were ordered, finding the right quantity from the same site to ensure continuity of finish and colour. They were found, transported at a cost, and the architects' charges rose with each redesign; as did the main contractor's, due to the care and cutting required in the brick- laying to fit the imperial bricks into a metric building frame.

As for the rest, the on-site recycling did happen. Slate cladding, roofing sheets and cast-iron drains were salvaged from the demolition of a building on site. Roofing timbers were sold to a pine furniture maker, and all the fittings inside, such as fire extinguishers, blinds, light-switches and sockets, were distributed to schools and hospitals.

According to the Building Research Centre, the hassle over the old bricks was worthwhile. The manufacture of new bricks causes environmental damage, which was averted. Besides, the reclaimed bricks give a mellowed character to the building. But, as they put it, they learnt that "greater insight is needed in the role of the reclamation industry in the UK".

So how does the building work? It is designed to harness the sun, the wind and water. When the south-facing, glazed facade is bathed in sunlight, inside it is cool. A borehole was sunk 70 feet to pipe cold water throughout the three levels. This groundwater pumped from the borehole as a cooling source is more efficient with a waveform construction of flooring, an organic form which provides interesting ceilings on the floor below. In winter, this water will be heated for underfloor heating, and piped into radiators. Mike Clift, project manager, admits that monitoring the success of this natural air-conditioning with airflow and temperature controls has just begun.

Any breeze is captured with cross-ventilation, a natural choice for the open-plan arrangements. The shallow office plan with fairly high glazed facades means that there is plenty of daylight indoors, and BMS-controlled windows on the third floor, with manually opened windows at lower levels, allow for cross-ventilation. Occupants can override the automatic control of all aspects of their environments; for the architects, this is "a most important issue for any building and one which a naturally ventilated building should address more effectively than a sealed box".

On the outside of the south-facing facade there are external motorised glass louvres and fan-assisted ventilation stacks, so on hot, still days fans inside will circulate the air through the offices. A small, thin film of silicone panels are photovoltaic, to store enough heat to light the building. In the summer the fire research unit was using this solar power to boil kettles for tea but these photovoltaic conditions are expected to generate 1,500 kilowatt-hours a year, enough to light the building. The new generation of compact low-energy fluorescents, T5, are more efficient than conventional fluorescent tubes and less environmentally damaging in manufacture. They are linked to presence detectors and to the BMS computer system, which switches off the lights when they are not needed.

It sounds like a building for the millennium, doesn't it? Let's hope it winters well.