This paper explores the densification of nontraditional post-war staircase entrance apartments in the Netherlands as a potential solution to the housing shortage. It examines the characteristics of nontraditional construction systems and their load-bearing capacities. The study employs methods such as literature review, research by design, and calculations. The results identify various densification strategies such as changing accessing, repurposing storage spaces, adding stories, and other extensions. The challenges associated with each strategy are analyzed. Calculations and literature research reveal that the foundation's capacity typically limits vertical extensions, recommending a maximum additional weight of 10-12%. Additionally, the inclusion of galleries is essential for certain densification types, with a maximum depth requirement of approximately 2000mm to comply with Dutch building regulations. The design project is about expanding and enhancing post-war staircase entrance buildings on urban and building scale, combined with a lightweight SIP construction method.