Two residential buildings in Sosnowiec — walls, stairs and balconies

Lightweight concrete changes that arithmetic at its base. A 10 cm wall in class LC12/13 weighs 140 kg per square metre against 235 kg for normal-weight concrete — over seven storeys the difference accumulates at every level and, across the building, runs into hundreds of tonnes. Smaller loads mean lighter walls on the lower floors, less reinforcement and shallower foundations, and every one of those is a line in the cost estimate.

The wall units arrived with window openings already formed and service penetrations prepared, which removed cutting and chasing on site. In a loadbearing wall every such cut is an intervention in the cross-section, permissible only within defined limits — and at seven storeys the walls on the lower levels are the most highly stressed, so that is where the tolerance for weakening is smallest.

Repetition of the storeys does the rest: the same set of precast concrete units returns to the hook on the next level, and the erection rhythm settles after the first floor and holds all the way up. Two buildings to the same layout mean that the moulds prepared for the first one work for both.

The stair flights and landings arrived complete, so the staircase rose with the structure — no formwork, and no waiting for concrete placed on site to gain strength.

Scope of work: lightweight concrete external and internal loadbearing walls, stair flights with landings, balcony slabs, transport and erection.