To explain the reactions of the building occupants to their acoustical environments, meetings with the designers, walk-through surveys, and detailed acoustical measurements were done. The objective was to determine how design decisions affect office acoustical environments, and how to improve the acoustical design of ‘green’ office buildings. Design-performance criteria were established. Measurements were made of noise level, reverberation time, speech-intelligibility index (SII), and noise isolation. Noise levels were atypically low in unoccupied buildings with no mechanical ventilation, but excessive in areas near external walls next to noisy external noise sources—especially with windows open for ventilation—and in occupied buildings. Reverberation times were excessive in areas with large volumes and insufficient sound absorption. Speech intelligibility was generally adequate, but speech privacy was inadequate in shared and open-office areas, and into private offices with the doors open for ventilation. Improvement of the acoustical design of ‘green’ buildings must include increasing the external-internal noise isolation and that between workplaces, and the use of adequate sound absorption to control reverberation and noise.