SIE/Home21 is a multifunctional building. It is also an ambitious social housing project that provides 244 units of exceptionally affordable housing for members of society who rarely have access to quality dwellings. This project is a part of the City of Vienna’s “Rapid Housing Program” (Sofortwohnbau-Programm); it was planned and built in an exceptionally short period of 20 months. It was the demands of this program that brought its diverse functions together under one roof. The Rapid Housing Program was a response to Vienna’s housing crunch of 2015-2016; it subsidized the pro tempere erection of housing upon underutilized, commercially zoned real estate. This housing could either be composed of temporary, mobile constructions or comprise permanent buildings with fixed-term occupancy for housing. Home 21 fits to the latter category. This fact underlies its use-neutral multifunctionality. The building will provide the city with housing for the first 10 years of its lifecycle, after which it must be capable of being economically converted into commercial property. This precondition required a simple, rapid and use-neutral construction.