The sound insulation performance of a specifically designed facade device, which allows natural ventilation but can provide relatively high-sound insulation, is studied experimentally in the present study. The experiment was carried out in two coupled rooms with one of them very reverberant and the other made semi-anechoic. The former acted as the receiver room and the latter contained a linear loudspeaker array (25 loudspeakers) as the noise source. The full scale facade device was installed on the concrete brick wall between the coupled rooms. Nine microphones were used to measure the average sound intensity inside the reverberant room. The effect of the size of the device opening (for ventilation) on the sound insertion loss was then determined by the difference between the average intensities with and without the device (an opened window). The present results show that the present facade device can offer additional acoustical protection of ∼12–13 dB(A) compared to that resulted from the conventional openable window design when exposed to traffic noise. The introduction of sound absorption materials at the top internal surface of the window cavity in general can result in a maximum of 2 dB extra benefit.