A common way to stabilize high rise buildings is to use an elevator core built of concrete. Today, we use to build these elevator cores of in-situ concrete. Precast concrete twin wall (double wall) is a semi-finished product that has become more common in recent years. This diploma work studies how the twin wall works out as structural elements in an elevator core. The work also shows some possible ways of designing twin walls and highlights some important parts of the design that will be vital to the stability of the building.     The result shows that it is important to think through where the element joints should be placed. The reason why this placement is important, is partly because of the stability of the structure and partly because the elements has to be mounted in a convenient way. The result also shows that it is more difficult to place the reinforcement in the twin walls than in an in-situ concrete wall. The consequence of this is that twin walls may need more space than an in-situ concrete wall to achieve the same load capacity.