Original building enclosures and past restorations and repairs to building facades require periodic evaluations to assess their safety, durability, performance, and aesthetics. Safety evaluations include review of gravity loads on terra-cotta cornices and seismic loads on stone anchors. Durability is a function of material properties such as permeability of sandstone or marble's dimensional stability. Performance requirements include watertightness of masonry, and aesthetics concern the selection of patching and replacement materials and sensitive design of structural strengthening.
Evaluation starts with visual observations from the ground augmented by close-up examinations such as inspection openings in masonry walls or borescope observations of terra-cotta anchors. Field tests used in the evaluation of exterior walls include moisture detection by infrared photography, wind pressure tests of veneers, half-cell measurements of active corrosion, and strain relief testing of built-up stresses in terra cotta. Laboratory tests are performed on materials removed from the exterior walls to evaluate their composition, the cause of distress, and the expected durability.
The final assessment of the building envelope is the result of a synthesis of observations, test results, and often mathematical analyses of the system and the materials.