PurposeIn response, this study developed a mathematical and computational method, through spatial configurations with justified plan graph (JPG), drawn from Space Syntax to extract essential information of the spatial topology of 13 valuable traditional courtyard houses located in Toon historical city of Iran.Design/methodology/approachHistorical vernacular housing has always been designed to incorporate and reflect the local lifestyle and cultural conditions. “Courtyard” is a fundamental part of traditional Iranian houses. This traditional building type includes a walled boundary and a complex of open, semi-enclosed and enclosed spaces. This study investigates the traditional houses in Toon historical town. Toon is one of the ancient towns in southeast Iran, including old courtyard houses in its heritage context. The spatial influence of the courtyard contributes to the formation of this famous architectural type.FindingsThe results show the remarkable impact of this space on dominating the plan of traditional Toon houses configuration compared to other spaces in all cases. Furthermore, spatial accessibility has changed over time, and the Safavid period had a higher level of integration and lower level of accessibility (mean i = 7.03) rather than the Qajar period (mean i = 6.34); also, privacy has decreased progressively.Originality/valueThe knowledge of characteristics of this historical architecture needs to be gathered for the preservation and conservation of the built heritage. Hence, the principle behind traditional Iranian courtyards was investigated to recognize the difference between the spatial influence of the courtyard and other spaces and the changes in the courtyard over time.