By: Grace Gallagher, May 27, 2020
Whether you realize it or not, when you are walking on New York City sidewalks you may actually be passing over a vaulted space that is concealed by the sidewalk adjacent to the building. These sidewalk vaults, as they are typically referred to, are typically constructed of steel beams and metal decking or even masonry arches that support the structural and sidewalk slabs above. Sidewalk vaults were commonly built in industrial areas to allow for delivery of materials, especially coal, without disturbing the occupants of the building. These days, many sidewalk vaults are used to house mechanical or electrical equipment, for storage, part of a commercial space and even some are abandoned spaces that have no use.
Since sidewalk vaults are a common feature of many commercial and residential buildings in New York City, proper maintenance of sidewalk vaults is imperative to ensuring the safety of the general public as well as avoiding water infiltration into the vault. The responsibility to maintain sidewalk vaults and the sidewalk slab above the vault in a safe condition falls on the owner of the building under Chapter 3 of the New York City Administrative Code. Sidewalk vault repair or replacement projects can be expensive, as sidewalks experience exposure to the elements throughout the year especially in the wintertime when de-icing salts are dispersed. Sidewalks and their vaults can sometimes sustain pedestrian and vehicular loads that exceed the vault’s load bearing capacity, resulting in deterioration or damage to the structural vault slab and supporting walls. Routine assessment and inspection of the vaults by qualified design professionals on a scheduled basis is highly recommended and will ultimately the building owner identify and address issues early on, minimizing the cost of the repairs.
When inspecting a sidewalk vault, architects and engineering can typically identify the obvious causes of deterioration such as water infiltration, corrosion of the steel beams, deterioration of the masonry arches, as well as weathering and aging of the structural elements. Water infiltration is one of the most common culprits for much of the damage observed in sidewalk vaults as many of the sidewalk vaults have not been properly waterproofed or protected from water infiltration.
Excessive deterioration of the structural components of a sidewalk vault can lead to failure of the structure and collapse of the vault, damaging the building’s property and potentially injuring those walking above the vault or occupants of the building. While not all damage and/or deterioration observed in sidewalk vaults will lead to imminent danger, it is still important to promptly address any conditions that are observed in order to prevent further deterioration.
At times, it is inevitable that the structural damage to the sidewalk vault is past the point of repair, with replacement of the structure being the only remaining options. In a sidewalk vault replacement project, the structural components of a sidewalk vault – namely, the masonry arches and steel beams – must be removed and replaced. Prior to the start of work, temporary shoring may need to be installed to properly support and protect the walls, ceiling, and any equipment in the vault. The sidewalk slab and masonry arches are demolished to reveal the steel beams, which are removed and replaced with new steel beams that are coated with a rust inhibitor. A new structural deck – either a corrugated metal deck with a concrete topping slab, or a newly-formed structural concrete slab – is installed over the vault and waterproofed prior to installation of the sidewalk slab. In vault remediation, the sidewalk vault is filled in with a concrete slurry, and a new sidewalk slab is then poured over the filled-in space. Prior to filling the vault, walls that are adjacent to the basement underneath the building must be examined to ensure that there are no voids that would allow the concrete slurry to travel from the vault to the basement space; any voids along the wall should be patched. Replacement of the sidewalk vault structure is the most labor intensive and therefore usually the more expensive option; however, the Owner could stand to gain long-term benefits from continued – or newly designated – use of the space. On the other hand, remediation of the vault ensures the structural stability of the vault and can often ease the Owner’s worries regarding future maintenance and operations of the space.
In any sidewalk vault repair or replacement project, it is important to consider the needs of the Owner. How are they currently using the space? Would they like to re-purpose the vault for another use? What additional work, if any, must be performed in conjunction with the vault work? Are all areas accessible? Are there any areas that appear inaccessible?
Once the Owner’s goals and priorities are defined, the engineers and architects designing the vault repairs can tailor the scope of work to fit the Owner’s needs. The common thread that runs through all sidewalk vault repair projects is that they are a necessity to ensure the safety of the general public and the occupancy of the building. At the end of the day, safety is everyone’s priority.