The practice of reusing processes and technical solutions leads to the formation of product platforms in house building. Product platforms originate from industries employing a make-to-order production strategy, e.g. the automotive industry. To test how the product platform concept is useful in engineer-to-order production strategies, a case study at two Swedish house-builders was made. Key factors that affect platform use in systems buildings were sought. The smaller company operates a supplier-led platform focusing on commonalities in process knowledge. There is less definition of the product itself to allow for distinctiveness in the product offer. The larger company has a decentralized business and operates a client-driven platform with fragmented standardization. Focus is put on creating commonality through defining the product and handling distinctiveness through an iterative design procedure. Product families were not in use at the case study companies. The companies transform standardized platform solutions into project uniqueness by using support methods. Four platform support methods emerged from the case studies: design planning, collaborative design, design optimization, and requirements iteration. The balance between commonality and distinctiveness in the platform is important to attend to in each house-building project. The engineer-to-order production strategy hinders the implementation of a fully parameterized platform. The product platform concept is therefore expanded with support methods to handle distinctiveness, i.e. project uniqueness. The product platform assets: components, processes, relationships and knowledge, are present also in platforms used in systems building