This research develops a spatial transformation model to work as a tool to address all possible layouts that can be expected when a building is changed. This tool provides tangible answers to the different spatial configuration possibilities of an apartment that can exist within one building design. It combines existing knowledge about the flexibility and adaptability of building elements with spatial and configurative information about an meant to generate alternative solutions. It can help the designer to explore variations, educate them on the different possibilities, support their decision-making, provide custom-fit solutions, and collaborate between different actors within a housing project. The main research question asked in this research is: “How can the extent of spatial alternatives of an apartment configuration be explicated within a building design?”. First an apartment building is deconstructed and its constituent parts are analyzed on their spatial flexibility implications. The second part of the research focuses on the definition and requirements of spaces. Every space inside a two person starter’s apartment is evaluated on their configurational, ergonomic, and legislative constraints. The third part of the research combines the building constraints and the spatial definitions of the room to build a layout generator. Finally the floorplans, that are generated by this model are evaluated on their validity and veracity. The overall functionality of the model is compared to an existing spatial flexibility assessment model and a spatial generative model.