The building envelope is a mix of construction units with different sound insulation properties. A window cannot be compared to more compact building parts such as external brick walls
or a roof construction.
The various building components will contribute with different levels of sound insulation. It is reasonable, therefore, that regulation of noise impact is made for the building as a whole – and not for the components alone.
A location on the roof will alter the outdoor road noise level – and the sound insulation required can be less for a window facing the back yard than for the facade facing the road. A typical change in the outdoor sound level would be -5 till -8 dB on the roof constructions facing the road and app. -15 db for the roof constructions facing the back yard (ÖNORM, 2006), see figure 4.6.
Legislation should take into account the fact that the various building components have different sound insulation properties, and that the variation of the outdoor sound level depends on the building location (city/country) and the location in the building envelope.