The Peggy Guggenheim Collection is located in the Palazzo Venier on the Grand Canal between the Church of Santa Maria della Salute and the Ponte dell'Accademia in the Sestiere Dorsoduro in Venice. Due to the annually increasing number of visitors and the resulting overloading of the existing structures, this design deals with a meaningful, identity-creating extension in the historical urban fabric. Lorenzo Boschetti designed the Palazzo for the Venier family in 1749. The dimensions of the building were so immense that it would have become one of the largest Palazzo in Venice. Due to financial problems of the builders only a part of the ground floor could have been built, which was however over the years over and over again formed and rebuilt. Part of the Thesis was to dismantle this palimpsest into its original components in order to understand Boschetti's design principles and use them for the current design. The original design concept could be analysed by means of floor plans and a wooden model, which can be found in the Museo Correr. In the design, the architect strongly oriented himself on the formal language of the Venetian master builder Longhenas and on the systematics of Palladianism. The most important design tool was an incommensurable principle of proportion, which manifested itself through a variable grid, which in turn was created according to the rules of the golden ratio (Fibonacci series). A similar principle can be found in the Le Corbusier mesh net. After the analysis of these principles, the extension of the Peggy Guggenheim collection could be continued in the same system.