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Hot-wire measurements were performed in a zero-pressure-gradient turbulent boundary layer overlying both a smooth and a rough wall for the purpose of investigating the details of inner–outer flow interactions. The roughness considered embodies a broad range of topographical scales arranged in an irregular manner and reflects the topographical complexity often encountered in practical flow systems. Single-probe point-wise measurements with a traversing probe were made at two different regions of the rough-wall flow, which was previously shown to be heterogeneous in the spanwise direction, to investigate the distribution of streamwise turbulent kinetic energy and large scale–small scale interactions. In addition, two-probe simultaneous measurements were conducted enabling investigation of inner–outer interactions, wherein the large scales were independently sampled in the outer layer. Roughness …