Walls in office building ended against ceiling plate - measured sound insulation

In Norway there are many experiences with office buildings with measured R'w around 32-37 dB between offices. Such values of sound insulation are measured for situations were the walls are ended against the ceiling, and not splitting the ceiling on both sides of the wall. In office building in Kristiansand with 40 mm Thermatex Silence (Dn,f,w 44 dB) as ceiling plate and walls ended against the ceiling, measured sound insulation between offices was R'w 41-45 dB. The reason for these good results is due to good sealing between wall and the ceiling plate of mineral wool. Experience from other situations with low sound insulation for such solutions, seems basically to be explained by sound leakage in the connection between wall and ceiling plate. It will be possible to achieve measured sound insulation between offices with walls ended against ceiling of mineral wool of at least R'w 40 dB or better, with good enough sealing between wall and ceiling and a good enough ceiling plate.