Background Constructive relationships between staff and young people in custody are a vital component of a therapeutic youth justice approach, which extends to the maintenance of a safe and secure environment (i.e., relational security). Despite the growing recognition that the physical environment of a facility impacts the procedures within a youth justice environment, as well as the relationships between staff and young people, there is a dearth of research in this area. Aims We investigated youth custodial staffs' views on, and approaches to, establishing relationships with young people while maintaining safety and security. The current study reports on the impacts and challenges highlighted by staff relating to the design of the facility. Methods We interviewed a total of 26 custodial staff members working at a Youth Justice facility in Melbourne, Australia. The semi-structured interviews were audio recorded and transcribed. NVivo 12 was used for thematic analysis. Two researchers (SO and PT) coded one transcript independently, iteratively creating a coding template using a thematic analysis approach. Once the final set of broad themes was constructed, the transcripts were re-examined, and narrower themes were identified. Results Thematic analysis revealed that a total of 14 staff (53.8%) identified the design of the custodial facility as impacting upon their ability to practice relational security. Identified design aspects included: unit size, quiet and private spaces, communal areas, green and outside spaces, ambience and spatial characteristics, spatial differentiation, facility and unit lay-out. Conclusion Youth custodial staff identified design aspects of a youth custodial facility that either promoted or impeded the ability to practice relational security approaches. The current study highlights the importance of carefully considering facility design given its impact upon staff-young people relationships, procedures and ways of working within these custodial facilities.