Effective greenhouse.

Log ID's work is consistent. The firm is concerned to generate houses and workplaces that use as much ambient energy as possible with a combination of active and passive collection devices (see for instance AR February 1993). Their green buildings are always literally greened with an abundance of planting which is considered not just as a visual amenity but as a means of reducing the carbon dioxide content of the air and increasing its proportion of oxygen -- even quite small alterations in the balance between the two gasses has been shown by some studies to improve the sense of well-being (and performance) of the inhabitants of buildings.

Shown here is a little intervention, in which the architects were asked to add an extra floor of accommodation to an existing one-and-a-half-storey office block tacked on to a long row of factory buildings devoted to pot galvanising on a Schlierbach industrial estate. It is a model of its kind, giving a previously dumb 1970s complex a degree of figure and presence, while suggesting a new form of office organisation.

The principles were simple. The new piece had to be lightweight, and fluid in plan, while giving people a sense of place (including the lovely view over the Swabian Alb). Log ID responded by making a building within a building on the roof of the existing structure. Lightness is achieved with a steel structure (galvanised with the firm's own process). Ecological correctness is ensured by making the outer shell a sort of greenhouse using normal insulated glass (K value 3.0) and the inner shell with glass of K value 1.3. The front faces south, so a louvred canopy projects from the roof to protect the interior f rom excessive insulation in summer, while allowing sun to penetrate in the darker months. The plan of the new floor is very simple. A strip of offices looks south over the landscape of the industrial park. Between the strip and the large factory to the north is another layer under the greenhouse, largely a garden of sub-tropical plants, watered automatically from a rain collection system on the roof of the factory.

The inner shell is quite heavily insulated, but the glass wall that divides the long volume from the outer containing one can be folded back to allow people working at this level to allow their places to become part of the garden space -- or not as occasion demands.

In summer, cooling air is drawn in from the roof through the openable lights and it falls down through the planting to oxygenate the atmosphere of the office strip before being expelled through the open windows on the south front. In winter, air is oxygenated and heated in the greenhouse outer shell before it comes to the people working in the offices. Background warmth is from waste heat generated in the factory next door.

The plan of the new floor is not entirely satisfactory: the projection of the fire-protected stair volume into the conservatory is not as lucid and convenient as it might have been. But the idea of one volume within another, with both feeding from each other in atmospheric terms, and in the pleasure that their interaction can give to the people who have to work in them is one that can be built upon.