Ask Habitat: What Should My Board Look for When Assessing Façade Damage?

HABITAT ANSWERS: Water is the nemesis of all building materials. Typically, the façade of a large residential building in New York City consists of brick or stone surfaces interrupted by window openings and the occasional area of decorative stone or terracotta work. Regardless of the combination of materials visible on the exterior, the hidden supporting framework is either steel or concrete enclosing steel-reinforcing bars.

The materials of the façade fit together to form components that deflect water toward the building’s exterior surface — away from the supporting framework. However, no building material is impermeable. As a result, over time, water that sits on and/or penetrates these materials works its way into the façade, attacking everything it touches.

The steel in a building’s structure is especially vulnerable to attack by water. Prolonged contact with water causes steel to rust. Rusting can cause steel to expand up to three times its original size.

In the process, the expanding steel puts increasing pressure on the surrounding building materials. This pressure, called “rust jacking,” compels those materials — whether stone, brick, or concrete — to move or bulge or crack.

Shifting or cracking of building materials forces open new points of access for additional water to penetrate the building envelope, speeding the deterioration process. The pace of this process speeds up when water freezes inside these new openings.

Freezing causes water to expand, enlarging the size of any openings it has infiltrated, and eventually making way for even more water penetration. This increased penetration leads to ever more shifting and cracking with each additional freeze/thaw cycle.

The resulting signs of deterioration, which you might see on your own building, fall into a variety of categories, each reflecting a specific type of damage:

• Vertical cracking, provoked by rusting and expansion of steel columns. This is especially prevalent at building corners lacking in expansion joints, where all the systems meet and one gives way as the others expand.
• Horizontal cracking at window lintels and supporting angles that hold up the brick or stonework above openings. Here again, the rusting and expanding steel puts pressure on the surrounding masonry, causing it to bulge, shift, or crack.
• Spalling, after water infiltrates glazed masonry or terracotta. The masonry backing expands at a different rate from the glazed surface, which eventually separates from the masonry. This separation allows more water into the material, only becoming apparent when the glazed surface falls from the façade. As a result, this problem poses a danger to the passing public while it greatly increases the permeability of the exposed materials.

Other less visible, but still eventually dangerous, locations for deterioration include:

• Fire escapes, which seem to be the last place owners want to spend their money. However, as exposed metal elements attached to the façade, fire escapes are uniquely vulnerable to the effects of weathering. The steps and platforms rust and deteriorate, as do the anchor bolts attaching them to the façade. With time and water, a half-inch anchor bolt can easily be reduced to the size of a needle.
• Cornices and water tables, decorative elements of stone, terracotta, or metal, like fire escapes, which are the most exposed and vulnerable components of the façade. They are not only exposed to wind and rain but also their projections provide opportunities for water to collect and sit against the adjacent building elements, weakening their structural connection to the façade.

Each of these problems starts out small and, while small, can be easily contained by small (and inexpensive) measures. Once building problems are allowed to fester, however, they take on a life (and a costliness) of their own.

As much as a good engineer may try to be sensitive to an owner’s budget constraints, every owner should keep in mind that, in the long run, preventive maintenance pays for itself. A tube of caulk is cheap and should be used when appropriate, but a tube of caulk will not help once a problem has reached the point where greater intervention is needed.

 

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