Conditional averages of longitudinal and normal velocities and of their products have been obtained with the VITA analysis for a centerline development of a boundary layer flow through a gap in an isolated wall-mounted roughness element. All measurements were made for a ratio of roughness height to boundary layer thickness 0. 135 at a Reynolds Number of 3 300, based on obstacle height and free stream velocity. It is inferred that conditional averaged patterns and higher-order moments are significantly affected by the difference of gap size G. In particular, the gap width effect on the peak ratio, mean event frequency and mean consecutive time for both accelerating and decelerating events at X/G=0 is completely contrary to those at X/G=4. The higher-order moments show the reverse tendency at the Y/δ≒0. 14 border.