Crystal box.

Houses chart the continuing, century-old romance of architecture and glass. This is an elegant, ecologically aware addition to the canon.

As an architect, Werner Sobek is informed by his conviction that, in formulating an architecture that is truly modern, which has a radical and positive relationship with the natural environment and inhabitants, architects must make demands on the wealth of technologies, materials and techniques available, rather than having recourse to tradition. (He has never forgotten Frei Otto's heartfelt plea, made in a speech for the Schinkel celebrations in 1977: 'Will you please stop building the way you have been doing').

This house in Romerstrasse, designed by Sobek for himself and his family, is set on a steep hillside overlooking Stuttgart. Rising four storeys high out of light woodland, it is a pure crystalline box which at night becomes an illuminated beacon. In spite of appearances, it is a green building, made of recyclable components; it is free from noxious emissions and energy efficient.

The sloping site presented problems, for as well as being at the edge of the hillside, it was at the end of, and some distance from, a steep narrow road. It contained a dilapidated and dangerous structure dating from the early '20s which had to be demolished with light equipment and a great deal of manual labour. But it provided a footprint for new foundations a concrete raft with built-in frost apron over a channel for cables and pipelines. Most of the foundation work had to be done by hand. There is no basement, so the building did not require deep excavations.

Being modular, the building could be erected quickly, (and, equally, dismantled and recycled). A steel frame stiffened by diagonal members stands on the concrete floor slab. The entire four-storey frame was assembled in four days. Floors of prefabricated wooden panels were then simply placed between beams, again without screws or bolts. Being modular, loadbearing and non-loadbearing elements are held together by easily detachable connections. There is no plaster or screed so no wet-trade waste. And no concealed installations -- cabling and pipelines are contained in sheet metal ducting along walls. Instead of light switches, fittings, door or window handles, the house is activated by touchless radar sensors and voice control.

The building is entirely transparent for, in addition to the suspended triple-glazed skin, there are no internal walls and space is defined by a few, strategically placed pieces of furniture. Entrance is from a bridge to the fourth floor and kitchen and dining room. Below, are living quarters, and below again, main bedroom, with children's and service rooms on the lowest level. All floors are linked by the vertical stairwell.

To create such a house, the architect had to devise a new way of managing energy without compromising aesthetic ideals and components, each by themselves innovatory, are worked into a coherent system. Triple glazing, with coated panels, has a k-value of 0.4. Solar radiation passing through the facade is absorbed by water-cooled ceiling panels and the energy transported through a heat exchanger to a heat accumulator which helps warm the house in winter. Ceiling panels act as thermal radiators and, says Sobek, there is no need for additional heating. Bath rooms are contained in a cubic unit, two storeys high; and all operations like flushing, opening doors, water flow and temperature, are controlled by sensors linked to a central computer.

Sobek says that the house was never intended to be a universal model - after all not everyone would choose to live in what would appear to be an elegant fish bowl. But it is an experiment that works very well on many levels and which has provided the practice with the opportunity of developing ideas for the future. As an exquisite architectural essay, it is a very personal manifestation of architectural, artistic and social convictions.