SIJ is a company that combines most of Slovenian steel industry, with headquarters at the site of a former screws factory. The original administration building was built in 1955, with an annex 10 years later, both attached to the manufacturing facility in length of 80 m. Both segments had pronounced structural design, the façade system of reinforced concrete columns gave facade rhythm, while horizontal structures were complex lattice structure. It was evident that during the construction period - due to poor foundation soil - emphasis was on reducing the total load, thereby also lowering the cost of construction at a time when cement was a scarce commodity. The analysis of the seismic safety showed that seismic restoration of the older part of the building was not viable, so we proposed the client to replace it. Construction of the newer part of the building was restored with carbon reinforcements. A composition of two volumes ensued, showing openly the difference in compositional tools of both periods. The existing building was renovated both structurally and in terms of building physics, so that it has retained the structural expression characteristic of the 1960s. The new building's function and geometry of construction design follow similar principles as the old building it replaces, but we decided to use composite structures - the vertical structural system of the facade was designed as round thick-walled tubes (one of the steelworks had produced guns for T 80 tanks), while horizontal construction systems and seismic core are of the reinforced concrete. The whole building is structurally designed in increments of 1,40 m, installations are arranged in the double floor so that it is possible re-arrange partition walls into new rooms without any intervention in the installation of heating systems, cooling, ventilation and lighting. As the building faces only due east, a 30% white print on outer glass of the double-ventilated facade ensures a pleasant working diffuse light and at the same time reduces the input of heat energy into the building. This also reduces the reflex of the glass volume, softens it and thereby generates an appropriate counterpoint to the sharper structural expression of the renovated building. Between the two volumes, a highlighted entrance canopy composition was envisioned as a smooth mirror-like base for the company logo and a nice division between the different compositions of both volumes.