The gravity method is used increasingly for site investigations in the development and re-development of urban areas. Typically, this work includes corrections for the terrain components of the gravity measurements. However, there is very little published reference material that describes the influence of existing buildings upon the gravity measurements. Hence, we conducted an experiment in a residential estate to evaluate this influence. The results show that the effects of buildings are significant and should not be ignored or underestimated. To achieve gravity data that can be attributed uniquely to geological variation in developed areas, we must first define the component caused by the buildings. It is hoped that the conclusions of this experiment will be useful to other geophysicists and help promote the use of gravity surveys in urban site investigations.