Abstract An increasingly popular solution for ventilation that facilitates strategies such as night cooling is the provision of purpose provided ventilation openings comprised of horizontal slotted architectural louvres. Often these are employed in single sided ventilation strategies where there exists an irregular unsteady interaction of wind and buoyancy forces. This paper presents results from full scale experimental measurements of the macroscopic Air Change Rate (ACR) for an opening utilising an architectural slotted louvre in zero2020/NBERT, a National Building Energy Retrofit Testbed in Cork, Ireland. 2 slot louvre cases and 3 plain opening cases were investigated with 44 tracer gas concentration decay tests completed in a single cell isolated office space. The findings show that, for similar boundary conditions, the spectral characteristics of the velocity in the opening are modified by the introduction of the slot louvre. A non-dimensional analysis highlights stronger wind dominant aeration for the louvre than a plain opening having comparable overall facade opening dimensions. On average across the various cases measured, the slot louvre ACR were 6.5% higher compared with the plain opening ACR with even greater increases when considering comparable free opening area cases specifically. A sensitivity analysis using stepwise multiple linear regression also demonstrated a high correlation between ACR, wind speed and wind direction for the slot louvre. A comparison of existing single sided correlations showed lower prediction error for the plain opening cases than for the slot louvre. When considering the dimensionless exchange rate parameter, F r , the published values for plain openings was comparable to those in this study but were too low in general for the slot louvre. An alternative value for this is suggested based on the field study measurements.