In architecture, the facade of a building is often the most important from a design standpoint, as it sets the tone for the rest of the building. Many facades are historic, and local zoning regulations or other laws greatly restrict or even forbid their alteration.
Highrise facades
In modern highrise buildings, the exterior walls are often suspended from the concrete floor slabs. Examples include curtain walls 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. An example of this is the First Interstate Bank Fire in Los Angeles, California. The fire here leapfrogged up the tower by shattering the glass and then consuming the aluminium skeleton holding the glass. Aluminium's melting temperature is 660 °C, whereas building fires can reach 1,100 °C. The melting point of aluminium is typically reached within minutes of the start of a fire. Firestops for such building joints can be qualified to UL 2079 -- Tests for Fire Resistance of Building Joint Systems. Sprinklering of each floor has a profoundly positive effect on the fire safety of buildings with curtain walls. In the case of the aforementioned fire, it was specifically the activation of the newly installed sprinkler system, which halted the advance of the fire and allowed effective suppression.
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.
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