17:59 Jun 2, 2015
This is a typical peculiarity with Swedish/Scandinavian building standards. In apartment houses, the main tapwater and sewage pipes are placed in vertical shafts that run throughout the building, from the bottom floor, all the way up. Thus, most piping can be completely hidden, as long as rooms with relevant appliances are located adjacent to this shaft. The name stam (Eng. trunk) is logical, considering that the main pipes runs vertically and branch out into the piping connecting the various appliances.
This has the advantage of less visible piping, which looks nice. Once in a while, however, every ten years or so, there will be "stambyte". This means that all the main pipes within the shaft are replaced. Bathrooms are usually refurbished as part of this process. Live long enough in Sweden, and you can be sure to experience the curse of stambyte!
Stambyte actually has an entry in Rikstermbanken:
Definition: byte av tappvatten- och avloppsrör
Anmärkning: Om nödvändigt värmerör i badrumsgolv. Byte av tätskikt i badrum. | 
