Top down construction is the reverse method of bottom-up construction in which the permanent structure is built from top to bottom of the basement along with deep excavations.
1. Early restoration of the superstructure is possible even before the completion of the building and the structures aboveground can be carried out simultaneously with the structures below ground. This greatly reduces the time for construction.
2. Concrete diaphragm walls are more cost-effective when they can simultaneously function as a groundwater cut-off and temporary soil retention system during the excavation phase of the project, and then as permanent underground walls with load-carrying capabilities for the finished structure.
3. Easier and economical construction of roof since it can be cast on prepared grade rather than using bottom forms.
4. The structural slab act as an internal bracing for the support of excavation, thus reducing the number of tiebacks required.
5. The virtually vibration-free operation minimizes the potential for ground movement and its resulting detrimental settlement.
6. It requires less width for construction area. Reduced environmental pollution associated with pre-construction earthworks.