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Cavity Check

The Department of Buildings is concerned about the safety of buildings built with cavity-wall construction. Can you explain what this is?

So in the old prewar days, buildings were built solid mass, three, four, five layers of brick. In the 1950s, engineers and architects wanted to come up with a lighter, quicker method of building, so they developed the cavity-wall system. Basically, there’s a cement-block wall on the inside, a two-inch air gap, then a brick veneer on the outside. And the brick veneer is tied back to the cement-block with galvanized aluminum wall ties, which keep the brick skin from peeling away and also keep it parallel to the backup wall.


Where do you find cavity-wall buildings?

They were built from the late ’50s to the 2000s, and they’re all over town. The problem is that the earlier generation cavity-wall buildings are now 70 years old, and the weak link in the system is not the backup block wall, because that's on the inboard side, resting comfortably without being subject to wind, rain or any of the elements. Meanwhile, the brick on the outside has become more porous, and the galvanized aluminum ties have rusted over time. Also, the early building codes required a tie every four feet on center, but later codes required a tie every two feet on center. As you can imagine, if the wall ties are rusting and deteriorated, all of a sudden the bricks can fall off and out. And there have been examples where bricks have fallen off buildings, either as a result of deteriorated wall ties, an insufficient number of wall ties, or just aging.


How do you discover if there’s a problem?

In the last Facade Inspection and Safety Program cycle, the eighth cycle, the Department of Buildings raised the bar on all architects and engineers. The DOB basically said, "We believe cavity-wall construction is in failure. Prove to us that it's not." So you were guilty until proven innocent, and I say that in a loving way because they were right. Now, instead of a visual inspection, we're required to do probes and report on the condition of the wall ties or the absence of ties.


Do you do the probes during the five-year FISP inspections?

Yes, this is a requirement for the new cycle, the ninth cycle. But we knew in the eighth cycle that the DOB was looking very critically at two things. In prewar buildings, they were going after the terra cotta, because they believed terra cotta was in failure. And they were going after the cavity-wall construction, and they wanted the architects and engineers to report on the wall ties.


If you do probes and find a problem with the wall ties, what’s the result?

Here’s a perfect example. We have a building that we started working on in 2018: 18 stories, red brick, late ’50s cavity-wall construction. We wanted to repair the spandrel beams (above arches) and their flashing. It was a $1.3 million project with about an 8- to 10-month timeline to complete. At the very beginning, we did  some probes and found that the wall ties were installed per the 1938 building code, which was legal at the time that the building was built. But it's no longer adequate because those ties were four feet on center, not two feet on center. The existing wall ties were more deteriorated than they should have been, and we were concerned that in the process of removing three or four courses of brick in order to access the spandrel beams to waterproof and repair them, the process would destabilize the rest of the brick, and it would fall down. So we had to present to the board this problem with the original construction of the building. A full reskin of all four sides would take the project from $1.3 million to $6 million, and from 8 to 10 months to 2 1/2 years.



Obviously not good news. But we came up with an option to reskin just the two street-facing facades, then, on the rear facades, we’re going to drill through the outer brick and put in new wall ties without having to take the brick out. Instead of going up to $6 million, we brought it down to $4.4 million, and a little less than two years. Everybody felt that it was a reasonable workout of the problem.


What would you suggest to boards in buildings from this era?

More and more of these buildings are getting to that age where the board could go on and on, spending a lot of money on mobilization and fixing and refixing the skin. Eventually they may come to the decision: "Listen, we have to reskin this building, and we may as well do it now rather than 10 years or 20 years down the road."

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