AkuLite Report 2, SP Report 2011:58
This study presents results from surveys made in 10 Swedish apartment buildings as well as field measurements in those buildings. The buildings have been selected by the manufacturers participating in two research programs (SBUF and AkuLite), being typical for their current productions and customers/ residents. The results of this study should be interpreted mainly with respect to these buildings since the selections of buildings and residents were not randomized. Bearing this limitation in mind, a few general conclusions are suggested about the noise protection offered by these types of building constructions. The results are complex and it is suggested to invite many parties to discuss them and to contribute to a comprehensive analysis. A few findings are highlighted and discussed.
Residents in the buildings with concrete floors and walls (built by NCC) were slightly disturbed by airborne noise from the neighbours and somewhat more disturbed by impact noise. Noise from technical equipments and traffic were more pronounced, taking compressor noise from the freezers and structure- borne sound from elevators and WC’s as examples. The overall ratings by the residents may be considered satisfying or good, but several improvements are suggested to reduce disturbing sources of noise that were observed. The design goal was in most cases to fulfill sound class B according to the national standard SS 25267 (4 dB better than the minimum requirements of class C). In most cases the buildings did not fulfill this sound class (B) in all aspects, but after some minor improvements the probability of reaching this goal and to get better ratings by the residents would increase.
Residents in buildings with timber joist floors and walls were slightly disturbed by airborne noise from the neighbours and technical installations. However, a main finding, impact noise cause considerable disturbance in all of the timber frame buildings, where about 25-30 % of the residents are very disturbed, about 25 % are disturbed and about 10% are somewhat disturbed. The measurement results indicated satisfying performance but this was not confirmed by the residents ratings. Further analyses are needed of the measurements techniques and weighing procedures described by the international standards EN ISO 140 and EN ISO 717, a research that is already in progress in the AkuLite program.
The results from these surveys were amended by data from previous studies to search for correlations between subjective ratings (by residents) and objective measurement results. A reasonable correlation was found between ratings and the calculated and/or the measured normalized impact sound pressure level (L’n,w + Ci,50-2500). From these results, it may be concluded that L’n,w + Ci,50-2500 53 dB is likely to serve as a minimum requirement. For airborne sound insulation (R’w + C50-3150), the correlation between the ratings and the R’w + C50-3150 was weak and no conclusion can be made with respect to the meaning of changing the current requirement. However, it is observed that new houses have better ratings than older with respect to airborne sound insulation in all buildings. Impact sound rating is better in new concrete buildings. This is certainly a positive result for the developers.
The questionnaire seem to work satisfactory. About 70% residents filled in the form and returned it properly. However, when a building is selected for a survey, it seems to be necessary to inform the residents beforehand, to explain the purpose of the study and to allow the residents to respond to at least one reminder. A few improvements have been made to the questionnaire after this survey was completed as well as some surveys in other EU member states. The average of the ratings turned out to be highly correlated to the fractions ”% of residents rating ≥ x”.
Listening tests and more detailed interviews with residents should be made to find out what reasons there might be behind the worst ratings of impact sound, whether it is a matter of its sound level, its frequency content or its time history. From our own impressions on site, it seems the speed of walking has a substantial effect on the annoyance from the impact sound in the dwelling below this floor. Only a slight increase of speed (impact force) changes the sound from barely audible to very unpleasant. There are many details to improve on to achieve better ratings from the residents, especially better workmanship and choices of technical equipment. Taking sounds from WC, air terminals, elevators as examples, they may all be efficiently attenuated at low costs. The planning process (the design) could be improved by small means.
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