Single sided natural ventilation configurations are very frequent especially in buildings in urban environments. Four single sided ventilation experiments were carried out in a full scale outdoor Test Cell facility. Air velocity measurements were taken at various heights in the middle of the opening. The average air flow rate through the opening was derived using the tracer gas decay technique. This work presents the results of an investigation into the relationship between the air velocity at the opening and the bulk air flow rate measurements. The paper presents a description of the experimental set-up as well as a qualitative discussion of the results.