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.