Is it okay to move your neighbor’s building?

This post is not about how people move structures, like the Hamilton Grange or Cape Hatteras Lighthouse, fascinating stuff. This post is about something that is occurring more frequently in New York City than in the past, it is unintended, and is directly related to the construction boom going on recently in the city. Although most of our work is on the design side, we have become increasingly involved in consulting to owners who share a lot line with (or are close to the lot line of) a construction site. And while there are precautions written into the building code¹, things can still go wrong, even with an excellent design team. There are a number of types of work that can affect the neighboring buildings: excavation, lack of information on the adjacent building, dewatering the site, underpinning walls, pile or mini-caisson installation, improper Support of Excavation methods, etc. Site specific factors include the type of soil present, the depth of the water table, how deep they contractors need to excavate to build the design as shown on the engineers drawings.

I believe that engineers should consider the ethics of their profession in deciding to take on a new project that will almost certainly damage an adjacent building, particularly an historic, load bearing masonry buildings such as townhouses, or religious buildings. Some, not all, developers of a site, will try to “skimp” on the monitoring of adjacent properties, doing the minimum that is required versus evaluating the susceptibility of the neighboring structure and modifying their monitoring accordingly (e.g., additional seismograph or optical survey points). And if the historic building happens to fall outside of an historic district, the engineer should still use the more stringent criteria for historic buildings issued by the City: TPPN-1088. If your client wants you to take shortcuts to save money and time, consider resigning.

I consulted to a client in a pristine, early 19th century townhouse when the neighbor on the other side of the party wall informed him that they planned to lower their cellar floor by nearly 20 feet. The engineers for the project told us, “relax, we do this all the time” and they proceeded with their work. Apparently they did not refer to the Viele Map of Manhattan, dating to 1865, that indicates the proximity of an old stream. They lost control of the soil beneath my client’s building, and did not provide sufficient lateral bracing to the party wall. The result, the building cracked from the foundation to the roof, with the worst movement at the rear where the soil migrated toward the excavation. I asked them to consider stopping at the depth they had underpinned to, not to continue deeper underpinning, and they refused, stating the program for the project required the space they were creating. The moral of the story: review the scope of work carefully before taking on a project. Inform the client that as the Engineer of Record, you would evaluate the adjacent building and then meet or exceed the City’s monitoring requirements.

Foundation wall crack:

Cracks opened suddenly at both the exterior and interior of the building: