Technical Booklet G Resistance to the Passage of Sound·Page 48·2.89
Reduced mass separating wall above ceiling
Where roof or loft space is not habitable and has a ceiling of minimum 10 kg/m² mass with sealed joints, the separating wall above ceiling may be reduced to 150 kg/m² mass but must still be a cavity wall.
Where the roof or loft space is not a habitable room and there is a ceiling with a minimum mass per unit area of 10 kg/m2 with sealed joints, then the mass per unit area of the separating wall above the ceiling may be reduced to 150 kg/m2, but it should still be a cavity wall (see Diagram 2.25).
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