The noise attenuation due to a barrier constructed parallel to a building facade has been studied to test for filling in of sound in the semireverberant space between the barrier and building. The excess attenuation in each13‐octaveband from 125 to 4000 Hz was measured and compared with the predictions of Maekawa. Measurements were also done with the barrier in a free‐field configuration, remote from the house. Results show that there is negligible filling in of sound and that the excess attenuation agrees well with the Maekawa predictions in both cases. The barrier was relatively light (2.5 kg/m2) and, although the performance was therefore limited by the transmission loss, the maximum excess attenuation ofA‐weighted levels was found to be greater than 19 dB.