Performance criteria for the window do not always mean that the same criteria are required for the window unit and all of its accessories – like subframes.

Specifiers mistakenly assume that the performance criteria indicated for the window unit itself applies to the entire assembly, including accessories. This can be problematic, particularly if the accessories are a critical element in the water resistance of the assembly (e.g. subframes and receptor systems). Designers typically indicate stringent performance requirements for the glazing system but fail to properly design or detail the interface between the glazing and adjacent construction. Field testing typically includes this interface at the test pressures specified for the window and leakage is common. Differentiating between window and interface leakage is difficult. Operable window and door components are not required to be tested in as stringent a manner as fixed components; however, specifiers often indicate the wrong test procedures and/or field testing is performed erroneously using the wrong procedures, resulting in false test failures.