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Vault lights are a unique sidewalk feature in former manufacturing districts of lower Manhattan. Inventor Thaddeus Hyatt first patented the vault cover in 1845 and continuously improved upon the design for decades thereafter. 

Vault light assemblies typically consist of cast iron plates with inset glass lenses supported by iron framing. The underside forms the roof of the sidewalk vault, and the topside is the walking surface. The glass lenses allowed natural light to illuminate the basement area located underneath sidewalks, adding valuable real estate to the building footprint. These assemblies, however, proved difficult to maintain and keep watertight. Despite advancements in materials and design refinements, water infiltration remained an issue. Once electricity and artificial lighting became an affordable option, vault lights fell out of favor. They were employed, however, for nearly a century and are an important feature of the cast-iron architecture found in the historic districts of SoHo and Tribeca.

The repair and restoration of vault lights can be complicated. Few contractors have skilled workers with the knowledge and experience to perform the repairs, and replacing cast-iron plates that deteriorated beyond repair is expensive. Sidewalk vaults must also comply with the NYC Building Code, which requires a minimum bearing capacity of 300 PSF for uniform loads and 8,000 (20 sq. inches) or 20,000 (20”x10”) lb. concentrated load (per BC Table 1607.1). The iron framing for vault lights was not designed to meet these requirements and will likely need to be structurally reinforced. An architect or professional engineer specialized in restoration can evaluate the existing conditions of a sidewalk vault assembly and provide a building owner with a conditions assessment and recommended next steps. The owner and A/E can then discuss available solutions, and a restoration program developed to address the specific needs of the project.

From a preservation point of view, maintaining the integrity of the original design intent of the vault lights is important. Due to high pedestrian traffic, movement from vehicular traffic, inclement weather, freeze/thaw cycles, and other adverse factors, a prudent maintenance program is required to keep the assembly watertight. If the extended basement space has been converted to a mechanical, electrical, or storage area, natural lighting may not be necessary. To comply with current codes and provide a continuous waterproofing membrane, pouring a structural slab under the vault lights may be an option. A repair and restoration program will require review and approval from the NYC Landmarks Preservation Commission and the NYC Department of Buildings.  

For a well-documented case study in NYC and a more in-depth look into the history of vault lights, Tech Notes from the National Park Service can be found online on the Repair and Rehabilitation of Historic Sidewalk Vault Lights.

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Sullivan Engineering provides high-quality building envelope restoration and compliance solutions.

We partner with facilities managers and account executives to provide technical expertise and project management for building envelope restoration, compliance, and maintenance.

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