METHOD TO PREDICT AIRBORNE FLANKING THROUGH CONCRETE FLOORS WITH NIBS AT THE BASE OF LIGHTWEIGHT WALLS USING ISO 12354-1

Typically in the New Zealand residential market, concrete floor systems with lightweight walls are the preferred construction method. As floor slabs become progressively thinner what consistently effects the achievement of the airborne acoustic design targets between adjacent residential units is the noise flanking transmission through the floor. A solution to limiting flanking is identified in this paper for when is not possible to have a slab of sufficient overall thickness, or when a floating floor or floating screed is not a cost effective option. The solution, utilising the introduction of a concrete nib along the wall line, reduces the floor to floor flanking noise transmission and promotes the achievement of better sound insulation ratings onsite. The objective of the research is to determine whether the scientific prediction method contained within ISO 12354-1:2000 - "Building acoustics - Estimation of acoustic performance in buildings from the performance of elements - Part 1: Airborne sound insulation between rooms" can be adapted to accurately predict the flanking reduction achieved through the introduction of a concrete nib into a heavy-floor/lightweight-wall system. The standard is under review, but from the draft available, the prediction approach for this specific application has not changed and the proposed method in this paper is still valid. Comparisons of predicted results with several field test results are made to verify the accuracy of the methodology. Incorporating a concrete nib into the wall-floor junction appears to effectively reduce the vibration transmission through the floor slab by introducing a secondary dissipation path for the sound energy running through the floor slab. Additional testing should be done to validate the theoretical model, however, based on the analysed data to-date, it appears that ISO 12354-1:2000 gives good correlation between the predicted and field-measured weighted sound reduction index when a nib is introduced at the wall-floor junction.