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What Lies Below, Part 2: City Infrastructure

by Jan Cermak

Most owners and developers that have developed sites in New York City realize the importance of understanding potential impacts of adjacent buildings, other structures, and city infrastructure on their development plans. These impacts may have a significant influence on what can be reasonably designed and constructed on any site.

The New York City Building Code includes a chapter (Chapter 13) that is fully dedicated to Safeguards During Construction and Demolition. This chapter discussed requirements for protection of adjacent buildings and infrastructure. Additionally, the NYC Department of Buildings follows more specific requirements for protection of historic and landmark structures.

Developers and owners are typically familiar with challenges of construction in dense urban setting next to existing buildings, retaining walls or building backyards. Negotiating access agreements with adjacent property owners is something that is often undertaken in the very early stages of design process. While these are typically prepared and negotiated by specialty real estate attorneys, engineers should review the technical language of such agreements (e.g., criteria for vibrations and building movements). The technical conditions of access agreements can significantly impact the design and construction.

New York City has extensive infrastructure which includes both above-grade and below-grade works (Fig. 1). New construction may have a potential impact on such infrastructure. When considering interaction with any development, the NYC Building Code requires that whenever construction is within 200 feet of NYC subway or other railroad tunnels/structures, approval and permit needs to be obtained from the authority having jurisdiction over the tunnel/structure. The presence of transportation infrastructure is generally easy to identify. However, establishing limits and depths of below-grade tunnels and other transportation structures can be a challenging and often requires some research (Fig.2 is an example of historic subway map showing subway location and profile).

In addition to rail/subway infrastructure, approvals may be required from agencies overseeing roadway tunnels and structures.

In recent years, new laws took effect to protect critical sewer and water distribution infrastructure requiring review of NYCDEP. When excavations or foundations are exceeding certain limits and a site is falling within 500 feet horizontal distance from the centerline of any water tunnel, an approval and permit is required from NYCDEP. Fortunately, there are historic and other records of City Water tunnels that allow us to determine whether this review is required. Water tunnels are in most cases deep enough not be impacted by typical building foundations. However, NYCDEP may also require an approval for construction adjacent or near other critical inrastructure, such as, large sewers. Since the location of such critical infrastructure is not well defined by NYCDEP, it is sometimes difficult to determine whether their review will be required or not. This uncertainty makes it difficult on some sites to evaluate impacts of critical infrastructure during the initial site studies.

In addition to NYCDEP, there are other utility companies such as ConEdison, National Grid or Empire City Subway that are responsible for maintaining underground electrical, gas and steamline conduits. These utilities may also impact construction on a site and review/approval of utility companies may be required. For instance, Fig 4 shows a regulator found along steamlines in NYC. A large vaults was found next to that regulator and required redesign of the building cellar.

As noted earlier, the presence of city infrastructure can influence what can be constructed on a site and may have major impact on the construction costs and schedules. Additonaly, the approval process requires time to complete. The agency review make take weeks to several months. Hence, it is important to consult with engineers and other professionals that have local experience with similar developments to understand this potential impact on site development. This can be often done in the very early stages of evaluating feasibility of developing a site.