Condor Tower in Perth, Western Australia provides an excellent example of how innovative engineering can be used to overcome the difficulties encountered in the retrofitting of reinforced concrete structures. Condor Tower was a 9 storey office building, to which 19 storeys have been added, converting the structure into a 28 storey residential building. During design, the need for new structural elements to carry the vertical loads was quickly identified. New infill party walls were utilised as load bearing elements. The interaction between these new elements and the old reinforced concrete columns could not be predicted with any confidence. The structure was expected to develop two vertical load paths as the new and the old concrete would have different shrinkage and creep characteristics. An investigation has been undertaken in conjunction with the University of Western Australia. On site strain measurements were taken over a four year period, building a large set of data on the behaviour of the building. Simple computer modelling has recently been completed which has aided in the explanation of some of the complex behaviour observed. In this paper the proportions of load sharing are quantified. It is shown that aside from elastic shortening, shrinkage and temperature effects dominated the observed behaviour. It is hoped that a better understanding of the load sharing behaviour between old and new reinforced concrete elements will permit more efficient designs in the future, leading to sustainable solutions for the redevelopment of existing buildings.