Department store, Graz

On sunny days in particular, many Graz residents are drawn to Schlossberg, or Castle Hill. Rising a full 123 metres above the historical city centre, the summit offers a wonderful panorama of the city's red-tiled roofscape, the River Mur and the surrounding area. The Kunsthaus (art gallery) by Peter Cook and Colin Fournier on the opposite bank of the river also vies for attention. Up here it is easy to see that any rooftop extension in old Graz is bound to be discovered. And since 1999, when Graz's historical city centre was declared a world cultural heritage site, objectors can call on UNESCO for support. If that organization decides that the proposal is not compatible with world heritage integrity it must either be changed or dropped.

A case in point is the extension of a tradition-rich department store in Graz's historical city centre. In 2005, Kastner & Öhler's board of directors decided to expand the sales area from 30,000 to 40,000 square metres. An additional storey and a unified rooftop landscape would unite the existing adjacent but independent buildings. An international design competition was subsequently won by the Spanish architects Fuensanta Nieto and Enrique Sobejano. Impressed by the structure of the old city centre and the deep, narrow, closely spaced houses with their steeply gabled roofs, the Madrid architects designed a folded rooftop landscape consisting of a series of steep gables of different heights. Skylights in the gables bring light down into the interior of the building and the two tallest gables sit atop new atriums containing the escalators. Three terraces cut into the rooftop landscape promise customers a panoramic view of old Graz.

But UNESCO did not approve of this proposed intervention in the cityscape. It found the volume and the chosen material incompatible with the world heritage fabric and threatened the City of Graz with – what else – the red list. Only when the volume was reduced by 35%, the height of the eaves was minimized and a different roofing material was chosen did it give the project the green light. The roof surfaces will now be covered with butt-jointed, anodised cast bronze sheeting. Preliminary work for the alterations has already begun and the opening is planned for the autumn of 2009.

The expansion of Kastner & Öhler is an asset not only for Graz's economic life but also for the architectural landscape. Nevertheless, a touch of bitterness remains for those familiar with the original design. It carried on a much more exciting dialogue with the historical roof landscape. As local architect Volker Giencke commented, 'this project in particular takes on the world cultural heritage title and develops it further. The project has such high quality that the claim of a loss of world cultural heritage is simply nonsensical.'