Despite the spatial and social restrictions it causes, single stall housing still prevails in sport and riding school horses, leading to the emergence of abnormal behaviours such as stereotypic or abnormal repetitive behaviours (SB/ARB). In the present study, we investigated the impact of the type (visual/tactile) and amount of social information that could be exchanged (i.e. distance between the individuals) on the expression of welfare indicators, including, but not limited to, STB. Additional observations were made on the production of snorts, recently described as a potential indicator of positive emotions, according to the type of stall horses were housed in. Two complementary studies were performed. One observational study on 32 sport horses, all living in the same place, being of the same breed and sex, whose aim was to compare the behaviours of horses maintained for a long time in two types of stalls differing mostly in the possibilities of contact with close neighbours versus looking outdoors. The second, experimental study, consisted in moving purebred Arab broodmares from one condition to another randomly every day for 66 days, the two types of stalls differing only by the possibility or not to put the head outside above the open top half door. The results show clear statistical relations between stall architecture and horses’ behaviour, especially STB, their prevalence and type differing according to the type of stall in both studies. Overall, the access to outdoor visibility and its degree (possibility to put the head out or not) had a major effect on the horses’ behaviours, which was the same in both studies, despite the differences between populations in terms of breed, sex and type of work. The experimental study also reveals that changes in behaviours can be rapid after a change of housing.