PRESERVATION TECH NOTES     HISTORIC GLASS NUMBER 2

 

Project Evaluation
Historically, when vaults lights deteriorated, a building owner would often cover them over with asphalt or steel diamond plate or replace them with a standard concrete sidewalk. By obscuring or removing vault lights from the sidewalk, an owner eliminated a significant architectural feature from the streetscape.

The project at 552-554 Broadway suggested another, more appropriate alternative: the sensitive repair and replication of the historic vault lights (see figure 14). The result was the return of a historically significant feature that exhibited a high degree of craftsmanship and complimented the building and streetscape. Furthermore, the repaired vault lights once again serve their original function of illuminating basement space beneath the city’s sidewalk.

Similar projects that included restoring vault lights have been able to recapture the basement beneath for restaurant, office and storage space, providing additional leasible floor area for the owner. They are showing that proper installation techniques and periodic maintenance can ensure the long-term performance of vault lights.

	Figure 14. The restored panels after work was completed.

Vault lights can be repaired using relatively simple, traditional technology. The tools and materials are commonplace: sanders, brushes, glass, paint and grout. The cast-iron, though often appearing beyond repair when covered with asphalt and rust, is usually sound and capable of restoration. Cracked historic panels, can be welded back together or new patches seamlessly introduced. Damaged lenses can be replaced with new lenses cast in custom molds by specialty glass manufacturers. When historic panels are missing, new ones can be fabricated, utilizing the same methods used to cast ornamental iron features and replacement pieces for cast-iron facades.

Stripping the cast-iron and reinstalling the hundreds of glass lenses are labor intensive undertakings that, depending on the size and condition of the panels, can be expensive. Additional costs would be incurred if the substructure of the installation requires reinforcement, repair or replacement.

The project described here took eight weeks from removal to reinstallation to complete. It involved a crew of three men to restore the panels offsite and a crew of four to reinstall them onsite.

Part of the reason that the fabrication of cast-iron-and-glass vault lights was discontinued was their propensity to leak. This problem was exacerbated by infrequent, misguided or nonexistent maintenance programs. After any vault light assembly is rehabilitated, it requires regular inspection and periodic maintenance. A small stock of lenses should be kept by the building superintendent. When a lens is cracked, the glass should be removed, the remaining grout cleared from the hole, the surface repainted and a new lens set in the same way as described above. Leaks that develop along the edge of the panel should likewise be repaired with the old material removed and new backer rod and grout applied. Lens and waterproofing repairs can often be completed without removing the panel from the sidewalk, and are neither expensive nor time consuming.

Conclusion
Vault lights are an important architectural features that are frequently overlooked and under maintained. Historically considered advantageous for the way in which they manipulated light and improved dark, potentially usable space, vault lights were also a visual complement to a building’s entrance and façade. Today, whether severely deteriorated, buried under layers of asphalt or missing altogether, this feature need not be lost forever. As the restoration project described in this Preservation Tech Note shows, sensitively rehabilitated vault lights can continue to provide architectural and historic character to the urban streetscape while serving their original function of naturally illuminating basement spaces.