To preserve the older building stock in Sweden in a sustainable manner, investigations of the construction and condition of these buildings are required. The investigations are needed to make correct decisions on maintenance of buildings and to evaluate energy-efficient measures for different types of buildings. In this work, the building stock in the city of Arboga, built before 1945 is investigated. Data about the building stock have been compiled using information from the building register of The National Heritage Board and the national database of energy certificates. Properties such as usage of the building, construction year, number of floors, area, volume and placement have been investigated and documented in an inventory list. The objective of the present study is to implement a method where the building stock can be divided into more manageable categories. The categorization is done by grouping the inventory in three steps: number of floors, location relative to other building and volume ratio. Based on the building categories, an archetype building is created for each category. With the help of these typical buildings, careful studies on energy-efficient measures can be performed. The results can then be extrapolated on the entire building stock. Delimitations have been made during the inventory. Outliers i.e buildings where the volume deviates much from the average in each category have been excluded. Finally, the method applied on 149 buildings resulted in four categories and four type buildings which represents the building stock of Arboga, built before 1945.