In modern highrise buildings, the exterior walls are often suspended from the concrete floor slabs. Examples include curtain walls, claddings and precast concrete walls. The facade can at times be required to have a fire-resistance rating, for instance, if two buildings are very close together, to lower the likelihood of fire spreading from one building to another.
Whether rated or not, fire protection is always a design consideration both in terms of concern for the subject building as well as for the surroundings, as falling glass can endanger pedestrians, firefighters and firehoses below.
Some building codes also limit the percentage of window area in exterior walls. When the exterior wall is not rated, the perimeter slab edge becomes a junction where rated slabs are abutting an unrated wall. For rated walls, one may also choose rated windows and fire doors, to maintain that wall's rating.