In Finland, requirements for room acoustics, sound insulation and noise levels in buildings are given in the National Building Code of Finland published by the Ministry of the Environment. In 1985, these requirements dealt with 13 building types, for example dwellings, schools and hospitals. During the 1990’s, the Ministry has developed the building regulation into functional direction. In the field of acoustics, this means that there are official requirements only for dwellings. After 1985, a new generation of architects, structural engineers and HVAC engineers has been educated. The lack of building regulations has resulted in the need of guidelines for acoustical design of buildings. The Finnish standard SFS 5907 with title “Acoustic classification in spaces of buildings” answers to this need by describing the required acoustical quality of the spaces by technical single-number quantities. The standard was written in co-operation with nearly all Finnish companies working in the field of acoustics. The Ministry of the Environment, research institutes and industry participated in the work as members of the advisory committee. The sale of the standard proves the big need of the guidelines: the standard became the most sold standard in the field of building and construction in year 2004 even though it was published in September. The standard is referred in specifications, invites for tenders and other documents. After the publication of the standard, industry and organizations have begun to prepare guidelines for construction of buildings corresponding to the standard. Even though the most buildings, e.g. schools, are designed without the participation of acoustical consultants, the increasing amount of guidelines does not decrease the need of acoustical consultancy. On the contrary, the Finnish consultation companies are growing as general interest in acoustical quality of buildings has become greater. The standard also makes acoustician’s work easier as it is not necessary to prove every detail to the client but the standard can be referred. The standard SFS 5907 is a recommendation, not an official requirement, and its use is voluntary. However, it can be concluded that guidelines and standards published by some institutions or organizations are documents that affect much people making decisions in building projects.