Buildings’ obsolescence and inefficient use can be prevented by designing general and adaptable plan layouts. General plan layouts accommodate different needs without being altered, while adaptable plan layouts can be easily altered thanks to, for example, demountable walls. A design-support method to quantify the generality and adaptability of plan layouts is the Spatial Assessment of Generality and Adaptability (SAGA) method Herthogs (Doctoral thesis. Vrije Universiteit Brussel, Brussels, 2016 ). To the knowledge of the authors, SAGA has not been used yet in a real design assignment. To understand how the method can support architectural decisions in a real design process, we applied an adapted version of SAGA in the transformation of a Brussels row house. In this paper, we describe the method’s relevance in validating the architect’s intuition by comparing the results of the method on the initial and future states of the house. Secondly, we evaluate the method’s added-value to guide the optimization of the plan layout, by comparing the future state with three alternative plan layouts. In this case, the architect considers the quantitative assessment as useful to evaluate and improve his architectural design, but the results are hardly interpretable without prior expertise. In conclusion, the method has potential in validating design choices fostering general and adaptable plan layouts. Depending on the expertise of the assessor, it can also support the optimization of the plan. In the future, implementing automatic checks or suggestions could bypass this reliance on expertise.