Sound insulation of multi-storey houses: Summary of impact sound insulation

Problems connected with the sound insulation of wooden multi-storey buildings are even more severe than those connected with fire safety. Evidently a wooden house can be built so that modern requirements for both the airborne and the impact sound insulation are met with sufficient margins. However, low frequency impact sounds produced by walking may be audible or occupants may feel them as non audible vibrations. There is still debate over what is the proper way to rate low frequencies and which of the rating methods is most appropriate. However, what is clear is that that the ISO rating method is not sufficient where wooden floors are concerned because of the results may be subjectively wrong. On the other hand, this does not mean that the impact sounds should be rated with more than one method. Therefore existing methods shall be developed into one sole method (Fasold's method) covering all types of floors. One of the main targets in the research project was to develop an impact sound insulation model of a multi-layered floor. An EXCEL-based system was developed with which it is possible to consider the effects of different sructural parameters on the impact sound pressure levels. The comparison between measured and calculated impact sound pressure levels shows promising results. However, the model shall be surveyed and verified with a more extensive sample of floors. It seems that walking on wooden floors causes low frequency "thumps", and that these floors are poorer, in this respect, than ordinary concrete floors. Measurements in laboratory and field were carried out with the floors carpeted and with and without the the floating structure. The purpose of these tests was to study the effects of different floor sub-systems (e.g. different floating floor structures, different heights and spacings of the joists, different ceiling structures) on the imapct sound isulation. The sound insulation properties of altogether 14 different wooden floors with some modifications to them were tested. There were not very many or so great differences between the floors concerning the airborne and the impact sound insulation. However, the wood-concrete composite slab behaves clearly better than the others. Addiotinally, a floor with a thicker and stiffer board on the top of the load-bearing sub-floor seems to function well.