How is a house from the mid-50s constructed? According to the description, the framework and floor structure are made of wood. Is it then a "plankhus?"
Houses from the mid-50s are almost invariably built with a frame structure, i.e., not a plank structure.
My house from 1953 is built with a wooden frame.
Then you should start tapping on the walls. However, the studs/planks are often hidden, so it's not always easy to interpret the tapping sound. If the house is a 1.5-story with about 115 square meters, you can assume it has a stud frame. This is because it was built with government loans, and one had to follow the National Board of Housing's regulations. The Swedish government was trying to reduce the use of wood in domestic construction so that more could be exported.
When I was looking for a house, I requested everything from the municipality's building permit archive; I think this should be standard practice for all home buyers. Hopefully, this will reveal the construction through the technical description, etc.
Contact your municipality and see if you can get hold of this before the viewing.
Contact your municipality and see if you can get hold of this before the viewing.