PRESERVATION TECH NOTES     HISTORIC GLASS NUMBER 2

Preservation Problem

	Figure 3. The individual cast-iron panels were displaced and coated in some areas with asphalt and concrete. A number of glass lenses were missing, allowing water to enter the basement of the building.

At the outset of the project, the vault lights at 552-554 Broadway were in poor condition (see figure 3). As with many old vault light installations, broken glass lenses and deteriorated seals allowed considerable water infiltration through the individual panels and the surrounding framework (also referred to as “saddles”). A majority of the glass lenses were either cracked, missing or replaced with a variety of materials including wood, concrete and asphalt (see figure 4). Of the twenty-one cast-iron panels, six sections had areas which were cracked or missing altogether. Two original vault light panels had been replaced with steel diamond-plate hatchway doors to the basement and a variety of materials had been applied over the remaining panels in repeated attempts to prevent further leaks. Worn and lacking a protective coating, the cast iron panels were exposed to the elements. Displaced panels and uneven asphalt and concrete patches presented trip hazards at sidewalk level.

Repairing and restoring the historic vault lights presented a number of obstacles. These included finding an experienced contractor, locating suppliers and fabricators for the glass lenses and missing cast-iron panels, and keeping the overall cost of the restoration program reasonable.

Consideration of building codes, and load requirements in particular, is part of any vault light restoration project. At 552-554 Broadway, loading issues were addressed in 1995 when the current retail tenant took over the space and installed a supplemental steel framing system beneath the deteriorated vault lights. This system involved the installation of a series of beams set beneath the edges of the individual cast-iron panels and supported by a large girder running parallel to the storefront. To meet stringent New York City loading requirements, other vault light restoration projects have included pulling up the vault lights for restoration, pouring a recessed concrete slab and setting the restored vault lights on top of the slab at the sidewalk level. Unfortunately, this treatment removes the basement daylighting character of the vault lights, but it does minimize water infiltration and maintains the historical character of the sidewalk.

Figure 4. A detailed view of one of the panels illustrates typical conditions prior to work. Although the original cast-iron knobs were still visible through the asphalt and concrete, many of the round openings were covered over or infilled. Nearly all of the remaining glass lenses were cracked.

Improving performance, safety and appearance were the main goals of the current restoration program. Water leakage into the basement and trip hazards at the sidewalk had produced a dangerous and unacceptable situation. Meanwhile, the deteriorated condition of the vault lights presented an unattractive entrance to the storefront and building.

Preservation Solution
An investigation of the vault lights and their support structure indicated that the assembly was repairable. Despite the appearance of the vault lights, physical deterioration was limited and the steel structure was in excellent condition. The project architect and preservation consultants contacted a specialist experienced in rehabilitating cast-iron who developed a plan to return the lights to their historic appearance and function. This eliminated the need for a concrete slab which would have cut off the light to the lower level.

To facilitate treatment and allow the sidewalks to remain unobstructed, the panels were removed and temporary steel plates were installed over the vaults. In the cast-iron contractor’s workshop, the surviving deteriorated glass lenses were removed, the cast iron stripped, cleaned and repainted, and new lenses set into the openings. Replacement lenses were cast by a specialty glass manufacturer, Blenko. The company had created glass molds for a vault light restoration several years prior and were now a regular supplier of various sized lenses for similar projects. A cast-iron foundry was contracted to fabricate two new panels to match the missing historic panels. Both new and repaired panels were delivered to the building site where the cast-iron specialist reinstalled them.

Repair Work and Replacement Panels

Contents

Print Version