The inside and outside velocity distribution was highly related with contaminant transport of naturally ventilated buildings. The building sidewall openings have a large impact on the velocity distribution at wind-driven conditions, but were not comprehensively investigated in previous studies. To achieve knowledge on that, a laboratory experiment was conducted using a building model in a wind channel. A laser Doppler Anemometer (LDA) was applied for the velocity and turbulence measurements. Tracer gas method (using CO2 as tracer) was applied to measure the air change rate. Eight configurations of the sidewall openings in varied sizes and locations in the sidewalls were investigated. Results showed that in the same outdoor wind conditions, the air change rate depended upon the inlet (windward opening) and outlet (leeward opening) sizes. The location of openings seems to have little impact on the air change rate. Even with the same size and location of inlet but different outlet, the velocity profiles ahead of building remain different. Inlet and indoor velocities with the same inlets were similar even in cases with varied outlet. The velocities at the outlet depended on the inlet sizes. The wake flow behind the building was highly depended on the size and location of inlet and outlet. It was recommended to consider the inlet and outlet size and location when investigate the contaminant transport from the inside of the building to the outside. (C) 2016 Elsevier B.V. All rights reserved.