Architectural Week 07 Belgrad
Vortrag in der Galerie O3ONE (www.o3.co.yu)
City Concentration – Building on the roof in Vienna

Building on the roof and high-rise building are contentious issues in Vienna. There is no question that adding space on the roof has many advantages: there is no need for additional roading, building land or infrastructure. The added space has more light, good views and, last but not least, a better potential concerning lay out.

Under what general conditions are roof extensions possible in Vienna?

Legal requirements
1. The zoning plan
This determines the nature of the development, for example, the permitted height of building. The problem is that many existing buildings already exceed the height restrictions.
2. Building regulations
These determine the quality of construction, including the standard of fire protection, thermal and sound insulation, fixtures and fittings, access requirements and so on. Along with this are regulations concerning structural stability and earthquake considerations.

Aesthetic form requirements
1. Listed buildings
Here, alterations to the basic building or to the roof are rarely possible.
2. Conservation areas
Here, alterations are often possible but the approval of the town planning department is necessary.
3. World Heritage Sites
In these sensitive areas every change is subject to public debate. There are no formal regulations, only recommendations and public pressure.

I have developed, for myself, four approaches for the designing of roof extensions.
1. Reconstruction within the existing building envelope. Here the only change to the envelope is, for example, insets for roof terraces and the projections of dormer windows.
2. The building is given a new roof form of which is developed from considerations of the main building’s form and structure.
3. An independent object is erected on top of the main structure. Here the main structure serves as a pedestal for the roof structure which forms the main feature of the building.
4. The new roof design is integrated into the original roof envelope to provide a merging of the new with the old.