Effect of presence of furnishings on designed and measured reverberation time in school spaces

According to Building Bulletin 93 (BB93), reverberation times for teaching and study spaces are expected to be assessed to comply with the pre-set requirements, when the room is finished and unfurnished. Presence of furniture and people is considered as a changed variable and therefore not included into assessment. Typically the teaching spaces are modelled by acousticians at the design stage (at RIBA Stage 3 and 4), taking into account only geometry and any surfaces' treatments proposed. During site visits (at RIBA Stage 5), when sample testing is conducted (especially in large halls or halls of complex geometry to confirm the necessary treatment), the spaces are not furnished. However during the testing, most of teaching spaces are fully furnished, and it seems impractical to test without the furnishings. The ways of taking into account the furniture and occupancy into reverberation time calculations and measurements, and recommendations on which stage it should be introduced into the design process are discussed in this paper. Examples of compliance on-site tests are provided.