Because of the noise from traffic lanes, railways or airports external walls of a building can also have regulations for sound insulation in the city plan. These regulations are based on the Government Decree No. 993/1992 of Finnish Council of State, according which the highest allowed A-weighted mean sound level in a residential apartment is 35 dB at day time and 30 dB at night. The city plan regulation means the difference between allowed sound levels outside and inside the building. To meet this regulation, the exterior of a building has to have a bit greater insulation capability than the difference is.

The insulation capabilities of exterior are dependent on its parts; the whole insulation depends on the wall structure of the facade, windows, doors and ventilation. Also areas of the structural parts have an effect on insulation. It is possible to determine the required insulation for every part by calculation.