In December of 2019, a woman was fatally injured in midtown Manhattan when a piece of terra cotta dislodged from a 17-story building façade and fell to the sidewalk. The building was cordoned off and a sidewalk bridge was immediately erected, but the tragedy underlined the ongoing need to vigilantly maintain New York City’s aging building infrastructure. The Façade Inspection and Safety Program (FISP) requires that buildings of six stories or more be reviewed by a qualified architect or engineer every five years, and that deficiencies be corrected shortly after. While this provides some assurance to owners, tenants, and passersby alike, it remains important for building owners as well as co-op and condo boards to understand what problem conditions look like and what the process is to correct them.
Let’s start with the basic building blocks. The term masonry refers to dimensional material of either stone or clay. Typical stone materials include marble, granite, limestone, and sandstone. Typical clay materials include brick and terracotta. The joints between masonry units are filled with a cement-like binder called mortar. Prior to the latter part of the 19th century, masonry buildings were constructed without internal steel, which meant that a building relied on bulky stone and brick outer walls to support the floors and roof. With the addition of a steel skeleton, the exterior walls could be reduced in thickness, larger windows were made possible, and buildings could be much higher.
While there are differences in density and porosity (for example, granite is a lot less porous than limestone, which is less porous than marble) all stone absorbs water. Brick also absorbs water in varying amounts, depending on density and brick face finish. Mortar has a granular composition, and thus promotes the migration of moisture outward once absorbed. Over decades, various construction innovations have been put into practice to more effectively eliminate moisture from exterior walls. For instance, the cavity wall is built with a continuous internal slot of space that directs water down and out the face of the building via flashing components and weep holes. The more contemporary rain screen is a wall type in which the facing of a building is constructed to stand off a water resistant air barrier, allowing drainage and evaporation.
There are various terms to describe the different types of masonry deterioration. A crack is a split in material, scaling is local flaking or peeling, and spalling describes material loss due to chipping. The term delamination is used to describe the complete removal of face material.
Almost all building façade problems are caused by trapped water. Building elements such as parapet walls, cornices, sills, and building corners are the most exposed to the elements, and therefore are the most vulnerable to water penetration. Water can enter as rain, melted snow, or as vapor that condenses in the wall. When water freezes it expands, so, if water manages to enter a hairline crack and freeze, the crack will grow larger. As this crack enlarges, more water can enter and freeze, expanding the crack further. Additionally, when water comes into contact with unprotected steel, it creates rust. Rust, similar to ice, expands and can therefore also cause cracking and spalling in adjacent masonry. This material displacement can lead to structural compromise and falling debris, so building elements supported by steel angles such as window heads and decorative terra cotta must be regularly checked. Any bowing out or sagging of a structure signals an underlying issue that should be assessed immediately.
Delamination poses a particular threat to brick. Bricks are made from clay that is heated to a high temperature in a kiln. During the firing process, a harder, denser, protective layer, called the fireskin, forms on the brick face. If water becomes trapped inside a brick wall, it can cause the fireskin to delaminate from the brick body, inviting rapid moisture infiltration. Incidentally, the same problem occurs when a brick wall is improperly cleaned with sandblasting or excessively high water pressure. Brick that has delaminated cannot be repaired. It must be replaced entirely.
While the Façade Inspection and Safety Program is required for buildings six stories and greater, it is just as important for smaller buildings to regularly monitor any signs of damage and to correct any deficiencies before they lead to failure. A typical review includes visual inspection from the ground with high powered binoculars, and physical inspection from fire escapes or through the use of a boom lift, scaffolding, or rope access. During the physical inspection, suspect areas of the building will be sounded with a hammer to determine underlying hollows and the severity of damage. Investigative probes may also be performed to study the substrate material. If a building is found to be unsafe, a protective sidewalk bridge must be installed immediately. Less severe conditions that require repair need to be addressed in a period of time specified by the inspector. In all cases, a qualified professional can help pull together construction documents, assist with bidding the work, and provide oversight during construction to ensure the work is in accordance with all building regulations.
Building owners who do not address problem conditions are subject to violations and fines, but unfortunately, this does not always provide adequate incentive to go through the appropriate process. The owner of the midtown Manhattan building noted above had received a violation notice eight months prior to the fatal accident. A regular review schedule and adherence to proper maintenance could have averted that tragedy, and hopefully we can avoid similar incidents in the future.