BACKGROUND: The physical environment is presumed to have an effect on aggression and also on the use of seclusion on psychiatric wards. Multicentre studies that include a broad variety of design features found on psychiatric wards and that control for patient, staff and general ward characteristics are scarce.AIMS: To explore the effect of design features on the risk of being secluded, the number of seclusion incidents and the time in seclusion, for patients admitted to locked wards for intensive psychiatric care.METHOD: Data on the building quality and safety of psychiatric as well as forensic wards (n = 199) were combined with data on the frequency and type of coercive measures per admission (n = 23 868 admissions of n = 14 834 patients) on these wards, over a 12-month period. We used non-linear principal components analysis (CATPCA) to reduce the observed design features into a smaller number of uncorrelated principal components. Two-level multilevel (logistic) regression analyses were used to explore the relationship with seclusion. Admission was the first level in the analyses and ward was the second level.RESULTS: Overall, 14 design features had a significant effect on the risk of being secluded during admission. The 'presence of an outdoor space', 'special safety measures' and a large 'number of patients in the building' increased the risk of being secluded. Design features such as more 'total private space per patient', a higher 'level of comfort' and greater 'visibility on the ward', decreased the risk of being secluded.CONCLUSIONS: A number of design features had an effect on the use of seclusion and restraint. The study highlighted the need for a greater focus on the impact of the physical environment on patients, as, along with other interventions, this can reduce the need for seclusion and restraint.