This study explores how the logic of product modularity could be useful for the design of complete residential building areas. Previous research has noted that product modularity is usually only applicable if a ‘full modularization’ approach is pursued (i.e., an approach with completely defined modules). This is challenging in Engineer To Order production strategies. Therefore, an approach towards partial product modularity is sought instead. In this approach, the modules are lesser defined to allow flexibility following, e.g., architectural design freedom, as well as per project-specific requirements posed in house-building projects. This study identifies nine (9) ‘modules’ which are denominated as functional spaces. By explaining how unique project requirements affect functional spaces, some integral elements of house-building are detailed. By evaluating the functional spaces in regards to the level of predefinition, as well as the level of relationship, their level of modularity is explored. The usefulness of partial modularity for house-building is suggested to be for coordination of design work and support tools that aides design work. This study suggests that partial modularity can be a feasible approach towards modularity without the need for countermeasures in terms of increasing product predefinition.