Exterior stairs should be designed and constructed such that the service life of the stair assembly is no less than the life expectancy of the building or structure to which they provide access, and are maintainable without non-visible damage occurring.  Increasing the ability of exterior stair assemblies to withstand prolonged exposure to moisture and other deteriorative elements will inevitably extend the service life of the assembly.  It is uneconomical to continuously attempt repairs, or to replace stair assemblies that have degraded to the point that they can no longer function as originally intended.  A typical failure of exterior stair assemblies occurs in stair designs that incorporate the use of a steel pan with concrete fill at the treads or landings.  Manifestation of the damage to this particular type of stair assembly appears as corrosion of the steel liners, freeze-thaw damages to the concrete fill, and structural weld and connection damage.  The corrosion will inevitably progress, causing unaesthetic conditions, decreasing structural performance, and ultimately threaten the public’s safety.  These negative attributes are further exacerbated when the stair system is designed with closed riser and stringer components.