The paper presents a mathematical model of process optimisation for the architectural layout of small apartments in the multi-family buildings in dense city centre housing area. The model was used to analyse and select an optimal version of the functional layout from 6 chosen solutions which are frequently used in the modern implementations of residential buildings. To solve the issue, the modified Chang's multicriteria comparative analysis - the EA FAHP (Extent Analysis Fuzzy Analytic Hierarchy Process) was used. The discussed model presents a new approach towards the issue which was so far lacking in the literature. Advantages of the adopted method of assessment were presented in the final conclusions.