Due to the Government Decree No. 993/1992 of the State of Finland, the highest A-weighted mean sound pressure level in residential room is at day time 35 dB and at night 30 dB. Because of the noise from cars, trains or aeroplanes in cities and near traffic lanes buildings? outer walls can have regulations for sound insulation. In these cases, regulations for outer walls have been set in the city plan. Fulfilment of the regulations can be checked by measuring the noise level of a speaker, which is placed outside, or the noise level of traffic.