A key to optimal use of the space in heavily urbanised areas is its smart planning. By providing an abundance of natural light and appropriate arrangement, even small rooms can be optically enlarged. That happened in this case. At the back of the terraced house in the centre of Amsterdam there was an extension, which deprived of natural light served the residents as a storeroom. By applying the D_F windows featuring solid structure and modern design, the building has gained not only use value but also quality in architecture. In addition, windows have been equipped with external screens to ensure protection against excessive heat.