Zigzag zenith.

This library and cultural centre translates disciplines of passive energy control normally associated with rural and suburban sites to the centre of a small German town.

The work of Log ID has regularly been shown in the AR's pages because this Tubingen practice has consistently pursued a policy of creatively investigating the potential of ambient energy (particularly solar) to create economical and humanly rewarding environments. But almost all of the firm's work so far has been one-off, isolated buildings in the suburbs or the countryside.

When the firm was commissioned to make a new library and cultural centre in Herten, it was faced with a new kind of problem. Herten is one of the Ruhr towns that is successfully moving from a clapped-out industrial base to one that promises hope for success in the twenty-first century. Part of the city's strategy has been to reinforce the existing structure of the town centre - a bit of a jumble architecturally, but one that has a strong, tight urban grain. Log ID had to find a solar-collecting solution for what they thought to be 'a shady site in the centre of the city'.

They chose to throw a great zigzag glass roof over the whole thing, and to create two contrasting volumes under it. The solid, concrete-walled library tower addresses the west-facing corner of Jakobstrasse and Hermannstrasse. Behind it to the east is the glazed drum of the cultural centre. A nick is articulated in Jakobstrasse to form Jacobsplatz, a little circular-organised urban space. A cafe opens to the west of the Platz (in summer its whole wall can be thrown open).

The cultural centre opens onto the little square too, but the usual route to it will probably be through the double-height free-form foyer that links entrances on Jakobstrasse and Hermannstrasse. From here, a route leads to the newspaper room and exhibition space, and to the stairs and lift to the upper levels of the library. The children's library is on the mezzanine, above that is the non-fiction section, with the main adult lending library at the top of the building. Each level has delightful study balconies within the drum of the cultural centre; the one on the mezzanine floor swells out to make an upper level of the cafe.

The balcony edges are lined with green plants that will eventually form a cascade down the interface between library and cultural centre (and provide a degree of acoustic absorption that will surely be welcome when music is played in the glass drum). The vegetation is part of an extensive layout of sub-tropical plants in the cultural centre. These are not only to make the place look agreeable but, as in other Log ID buildings, are intended to increase the oxygen content of the internal atmosphere which the architects believe improves the wellbeing and performance of a building's occupants.

The huge glass roof hovers over the building proper and in the void between it and the roof proper are solar collectors that heat domestic hot water and air which can be circulated to the interior. The drum walls have (for glass) a very low U-value (1-1.3 W/[m.sup.2]degK) and on sunny days in winter, both it and the library are warmed by the solar-heated air, which in autumn and spring is supplemented when necessary by a conventional air warming system. The mass of the concrete structure of the library tends to keep its spaces at an even temperature and heat losses to the drum are minimised when the cultural centre is not in use on cold days by simply shutting the doors to the balconies. On very hot days, the glass roof of the drum can be opened so that it acts as a solar chimney and is self-cooled by convection.

The Herten building has a complex human programme which has been addressed with a brave and innovative building. (It is plainly more difficult to create a building of diverse functions that uses assisted passive energy than to deploy such systems in, say, an office building.) Only time will tell whether Log ID's daring will pay off.