is substantially co planar with a floor level of the public corridor 25 also in each of the apartments 10 a and 10 b the floor level of module a and the floor level of module b extend from the public corridor 25 to a building facade on a first side of the public corridor 25 on which an entry 34 from the public corridor 25 into the apartment is situated see fig3 b a floor level of module c of each apartment 10 a and 10 b extends beneath the public corridor 25 to a building facade on a second side of the public corridor 25 opposite to the first side such that the floor level of module c extends in a direction opposite to the direction in which the floor levels of modules a and b extend from the public corridor 25 the floor level of module d of each apartment 10 a and 10 b extends above the public corridor 25 to the building facade on the second side of the public corridor opposite to the first side such that the floor level of module d extends in the same direction as the floor level of module c extends from the public corridor 25 a stair system is arranged in each apartment 10 and 10 b to connect the floor levels therein see for example fig1 and 2 although preferred embodiments.