Protecting the Public: What You Can’t See Might Hurt You
July 19, 2016
Hidden failures: The invisible deterioration of NYC facades
The facades of 14,000 buildings in NYC are inspected on a regular basis under the facade Inspection Safety Program (FISP). How many of these buildings pass muster? The Department of Buildings (DOB) recently announced that many of these buildings have aging materials that can be expected to fail without proper intervention.
At an industry-wide meeting in April 2016, the DOB requested that professionals involved in FISP inspections during FISP Cycle 8 keep their eyes open for the following failing building systems:
Cavity walls. Cavity walls are commonly constructed of masonry (such as brick or stone veneers) that are designed to allow moisture into the system and provide a way to drain it back out. Cavity walls typically have two layers: a “back-up” layer, which provides support and strength, and an outer-facing “skin.” In between these two layers is a cavity (an air space or insulating plane) that creates a drainage plane, directing the water to drain out through weep holes at the bottom. The two layers of masonry are held together by “wall-ties,” metal strips or bars.
The Department of Buildings (DOB) is concerned about the degradation of these wall-ties when subject to damp conditions over long periods of time. Commonly made from iron and steel, these metal ties are usually galvanized and sealed with a protective coating to resist corrosion. Over time, however, this protective coating can deteriorate, leading to wall-tie failure. Wall-tie deterioration is often difficult to detect, although it can sometimes be detected by a bulging wall, wall movement, or step cracking.
Properties that were built using galvanized-steel “fishtail” ties (1920s–1950s) or galvanized wire “butterfly” ties (1960s–1980s) are especially susceptible to corrosion. Wall-tie deterioration can seriously impact external walls, making the “skin” unstable and susceptible to collapse.
Terracotta. A recent spate of building decorative stone failures and fatalities have put architectural terracotta high on the DOB’s radar.
Terracotta (from the Italian word for “baked earth”) is a clay-based glazed ceramic used as a building material in older buildings. Popular between the late 19th century and the 1930s, glazed architectural terracotta offered a modular, varied, and relatively inexpensive approach to wall construction that was particularly adaptable to rich ornamental detailing. It is one of the most prevalent masonry building materials found in the urban environment today.
Terracotta glaze is impermeable, but as the glaze starts to wear off or fracture, the terracotta becomes increasingly subject to the ravages of water and weather. Even the joints between the pieces can become weathered, allowing moisture to seep in and cause deterioration of the anchorage.
Each case of deterioration is unique, depending on the particular type of terracotta and the various factors involved. Architectural terracotta varies widely based on its method of manufacture, inconsistencies in its original installation, the number of component parts, and any ongoing repairs. Although terracotta deterioration is most commonly caused by water-related problems, there are also other, less-frequent (but no less severe) causes. Faulty original craftsmanship, although difficult to document, is often cited as a cause. Other common causes include stress-related deterioration, damage caused by later alterations and additions, and inappropriate repairs.
The DOB emphasized that a proper program of building maintenance requires keeping a watchful eye out for wall cavity failure and the deterioration of ornamental terracotta facades. In addition to regular FISP inspections, building owners and property managers should report any signs of possible deterioration to their building architects and engineers for closer examination.
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