The influence of thermal insulation selection on a facade sound insulation property – theoretical case study

Impact of the external thermal insulation composite system (ETICS) on the sound 
reduction index improvement is widely discussed topic. ETICSs are already several 
years commonly used to reduce buildings thermal loses. However, its application 
can negatively influence facades sound insulation properties. In the high frequency 
range  an  additional  thermal  insulating  layer  improves  the  sound  insulation 
property. However, in the low frequency range the sound insulation spectra rather 
often decrease. This decrease is caused by a mass - spring - mass resonance of the 
ETICS  system.  Location  and  the  depth  of  resonance  dip  depend  on  the  ETICS 
composition.
Several  prediction  models  and measurement-based case  studies  were  published 
already.  In  this  contribution, an  analytical  model  is  used  to  predict  the  sound 
reduction index, using a measured dynamic stiffness of the ETICS system. A number 
of different thermal insulating layers are analysed having similar thermal properties 
but  different  material  dynamic  stiffnesses and  loss  factors.  The  comparison  of 
theoretically  predicted  sound  insulation  spectra and  the  impact  of  the  dynamic 
stiffness measurement technique are presented.