Regarding stair railings, the building code (BBR) states:
"Railings on stair flights should be at least 0.9 meters high. If an opening beside a stair flight is larger than 0.4 meters in both length directions and the floor height is more than 3.0 meters, measured from floor to floor, the railing should be at least 1.1 meters high.
Railings on stair landings within the individual apartment should be at least 0.9 meters high. If the floor height is more than 3.0 meters, measured from floor to floor, the railing should be at least 1.1 meters. Railings on stair landings outside the individual apartment as well as railings on balconies and gallery access should be at least 1.1 meters high."
Therefore, stair railings should be 1100 mm if the floor height is more than 3 meters, otherwise 900 mm. Handrails should be at a height of 800 mm.