552-554 BROADWAY 

New York, New York 

Introduction 

Beginning in the 1850s, sidewalk 

vault lights became a common feature amidst the burgeoning manufacturing districts of America's urban 

streetscapes. These cast-iron panels, 

fitted with clear glass lenses, were 

set into the sidewalk in front of 

building storefronts. They permitted 

daylight to reach otherwise dark 

basements (or "vaults") that extended out beneath the sidewalks, creating more useable or rentable space 

for building owners. 

Each panel was screwed to a castiron saddle and the iron framework 

that spanned the basement vault. 

They were cast with molded iron 

knobs around each lens to protect the 

glass and improve the footing of 

passers-by. Originally simple glass 

lenses were set in the panels, usually 

with a cement grout. Advances in 

day lighting technology including the 

development of prismatic glass pendants that refracted the sun's rays 

further into basement areas, and the 

Technical Preservation Services 

Preservation 

Tech Notes 

HISTORIC GLASS 

NUMBER 2 

Repair and 

Rehabilitation of Historic 

Sidewalk Vault Lights 

Cas Stachelberg 

Higgins & Quasebarth 

Historic Preservation Consultants 

Chad Randl 

Technical Preservation Services 

National Park Service 

Deteriorated historic sidewalk 

vault lights should be repaired 

wherever possible. Missing panels 

can be replicated with new panels 

that match closely the detail and 

overall appearance of the historic 

vault lights. 
use of reinforced concrete panels 

made vault lights popular through the 

1930s. 

Located in New York City within 

the SoHo Cast-Iron Historic District, 

552-554 Broadway is a six-story loft 

building detailed with Italianate ornamentation on the upper floors (see figure 1). Designed by the architect John 

B. Snook and originally constructed in 

1855 as two separate buildings, 552 

and 554 Broadway were joined internally and unified in 1897 with a new 

two-story, cast-iron storefront and sidewalk vault installation. It is likely that 

the building's basement was used historically for a combination of light 

manufacturing and storage. 

The original vault lights stretched 

approximately fifty-four feet across the 

full width of the ground-floor storefront. They were made up of twentyone individual panels extending five 

feet from the building line and varying 

in width from l' 1 0" to 2'8" (see figure 

2). The cast-iron panels were fit with 

1-1/2" diameter glass lenses, typical for 

historic vault lights. Raised lettering 

on the panel frame, "Jacob Mark, 7 

Worth Street, New York," indicated the 

foundry's name and address in 

Figure I. A cast-iron storefront was added to 

552-554 Broadway in 1897. The storefront 

included a fifty-four foot long assembly of 

cast-iron vault lights set in the sidewalk. Glass 

lenses in the panels allowed light to enter the 

basement area, increasing rentable space for 

the building owner. 

2 

Figure 2. At the outset of the restoration project, the original cast-iron and glass vault 

lights in front of the building's storefront were 

in poor condition. 

Manhattan. Over one hundred years of 

pedestrian traffic, deliveries and environmental exposure took a toll on the 

vault lights at 552-554 Broadway. 

With use of the basement for merchandise storage, the current ground-floor 

retail tenant initiated a vault-light 

restoration program in 2002 to return 

this historic sidewalk feature to its 

original function and appearance. 

Problem 

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. 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 twentyone 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 

panels and supported by a large girder 

running parallel to the storefront. To 

meet stringent New York City loading 

requirements, other vault light projects 

have included pulling up the panels for 

restoration, pouring a recessed concrete 

slab and setting the restored vault 

lights on top of the slab at the sidewalk 

level. This treatment minimizes water 

infiltration and maintains the historical 

character of the sidewalk but removes 

the daylighting function. 

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. 

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 beneath 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. 
Figure 4. A detailed view of one of the panels illustrates the 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. 

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. 

Figure S. Workers removed any remaining corrosion, grout and other contaminants 

with hand chisels and power~perated wire brushes. 

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 Glass 

Company. 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 

The first step in repairing the vault 

lights at 552-554 Broadway was to dismantle and remove the panels from the 

sidewalk. Over two days, a crew of 

five experienced workers drilled the 

heads off of the panel bolts and gently 

pushed them through the holes in the 

cast-iron framing. After the bolts were 

removed, one comer was loosened by 

inserting a chisel between the saddle 

and the panel. Other chisels were 

worked around the other sides of the 

panel. Then, two workers raised the 

panels, each weighing approximately 

three-hundred and fifty pounds. Each 

panel had to be lifted straight up out of 

its frame because any uneven pressure 

could have cracked the cast-iron. A tag 

with an identification number keyed to 

a drawing was secured to each panel to 

ensure reinstallation into the same 

opening after repair. The twenty-one 

panels were packed upright into the 

back of a truck and delivered to the 

repair shop. 

The sidewalk at 552-554 Broadway 

had to remain accessible to pedestrians 

while the vault lights were restored offsite, so a 3/4" thick plywood sheet 

topped with 3/16" steel diamond plate 

was placed over the openings. The 

temporary covers were tack welded 

into the comers of each hole and the 

seams were sealed with a flexible 

polyurethane-based caulk. 

When the vault lights arrived at the 

repair shop they were placed upside 

down and the surviving glass lenses 

were knocked out by hand. A variety 

of materials, used in the past to fill 

holes where lenses were broken or 

missing, were also removed. Next, 

each panel was sandblasted. This 

3 
Vault Light History 

Cast-iron vault lights were originally 

patented by Thaddeus Hyatt in 1845. 

As envisioned by Hyatt, the system 

incorporated small glass lenses set into 

cast-iron panels. The panels were modular, allowing for installation over large 

areas. Vault lights, sometimes referred 

to as "Hyatt Patent Lights," became 

widespread through the second half of 

the nineteenth century, paralleling the 

rapid development of cast-iron architecture (see figures a and 

b). As detailed in numerous historical trade catalogues of the time, vault 

lights were marketed to 

building owners and 

architects as a safe, inexpensive daylighting system that allowed for the 

conversion of previously 

"unusable" basements 

Figure a. 

subway system (see figure d). 

Purposefully employed by the designers of the Interborough Rapid Transit 

Company's (IRT) subway, vault lights 

were constructed in the ceilings above 

the platforms to create an inviting 

underground space for a public unaccustomed to subterranean travel. 

Along with decorative amenities and 

the promise of rapid transit, the subway depended largely on pure, natural 

light to attract its riders. 

/ 

into "rent-earning, productive work space." 

Prismatic pendant (or 

"saw-tooth") lenses were 

often used in place of the 

basic lenses because the 

angled projections on the 

underside of the prism 

bent light rays, directing 

them to the inner reaches 

of the lower levels (see 

figure c). 

"HYATT" REFRACTING LENS. 

With the emergence 

of Portland cement as a 

new building material at 

the end of the nineteenth 

century, vault lights were 

increasingly constructed 

with round, translucent 

glass lenses set into reinforced concrete. The new 

concrete-and-glass version improved durability, 

waterproofing and slipresistance while producing the same illuminating 

effect. 

Vault lights were also 

widely employed in the 

early 1900s construction 

of New York City's first Figure b. 

cleared off the paint, chewing gum, tar, 

asphalt, concrete, corrosion, grout and 

other grime that accumulates on a New 

York City sidewalk over the course of 

a century, without pitting or otherwise 

damaging the cast-iron. Then, workers 

cleaned each of the panels with small 

chisels and drills fitted with wire brush 

attachments to remove any material 

missed during sandblasting (see figure 5). 

At the outset of the restoration program, six of the twenty-one vault light 

panels were found to be cracked. 

Rather than replace them with newly 

cast panels, the contractor chose to 

repair the damaged units using two different techniques: welding cracked sections and splicing in replacement 

4 

pieces. Due to inconsistent heating 

and the presence of impurities in the 

blast furnace mixture, historic cast-iron 

is a notoriously brittle material. This 

brittleness makes historic cast-iron susceptible to cracking and a challenge to 

weld properly. 

The contractor had developed a system for repairing cracked or damaged 

vault covers. Primary considerations 

were to ensure that the pieces to be 

welded were correctly positioned and 

level and that the cast-iron was properly preheated. Then, using a wire-feed 

MIG (metal inert gas) welder, the two 

pieces were joined together (see jigure 

6). The welded seam was ground 

down to the level of the adjacent panel 

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Figure c. 

Figure d. 

surface so that the repair would not be 

visible after painting. The result was a 

strong, durable and complete cast-iron 

panel. When replacement sections 

were required, the contractor drew 

from a small stockpile of salvaged panels identical to those at 552-554 

Broadway. 

When repairs to the cast-iron were 

completed, two coats of primer were 

applied, followed by three coats of 

gloss black paint to match the existing 

paint color (seejigure 7). The contractor used a Benjamin Moore system 

including an "ironclad" oil-based metal 

primer and alkyd gloss enamel 

(Impervo) top coat that offered high 

abrasion resistance. A rust conversion 
Figure 6. Cracked panels were repaired by 

welding in new material from a stock of 

salvaged panels maintained by the cast-iron 

contractor. The welded seams were then 

ground down before repainting. 

Figure 7. Cleaned and repaired panels were 

painted with two coats of oil-based metal 

primer and three alkyd gloss enamel top coats. 

Figure 8. Before the glass lenses were set, a 

ring of silicone was placed along each flange 

on the lower edge of the opening. The silicone 

kept the lens centered in the cavity while a 

waterproof grout was used as the main sealer. 

Figure 9. A caulk gun helped workers apply the 

waterproof epoxy grout around the lenses. 

coating system would also be suitable. 

Painting was followed by the resetting 

of new glass lenses. 

After ensuring that the panels were 

dry and free of oils, dirt, dust and other 

contaminants, a bead of silicone was 

applied at the bottom of each of the 

round openings (see figure 8) . This 

preliminary seal would keep the glass 

centered during the grout application. 

Replacement lenses were obtained 

from a specialty glass manufacturer 

that has supplied new lenses for a number of vault light rehabilitation projects. The glass lenses were set into 

place and a two-part epoxy grout was 

used to seal them in the panel and 

waterproof the joint (see figure 9). The 

gray, chemically-resistant material was 

the same used for grouting floor brick, 

quarry tile pavers and ceramic mosaics. 

Workers mixed the compound, placed 

it in a caulk gun and squeezed it into 

the areas adjacent to the lenses. Before 

it hardened, excess grout was removed 

using a dampened sponge (see figure 10). 

After twenty-four hours, the grout 

cured sufficiently to complete the 

reglazing process. The panels were 

turned over and workers used a razor 

blade to cut away excess silicone that 

had dripped out of the space between 

the lens and the cast-iron along the 

underside of the panel. Then, the panels were shipped back to New York 

City. 

Replacement Panels 

Because vault lights are no longer in 

regular production, new custom panels 

had to be fabricated to replace the two 

missing when the project began. The 

contractor chose a surviving panel that 

was in good condition and sent it to a 

foundry in Alabama for use as a pattern. The foundry, which had worked 

Figure 10. The grout remained water-soluble 

until it hardened, enabling workers to remove 

excess material and smooth the joint between 

the lens and cast-iron with a sponge. 

on a number of vault light projects in 

the past, cast two new panels using 

techniques that had changed little in 

the past century. The original sample 

was packed in a bed of casting sand to 

make a three-dimensional mold. To 

account for shrinkage in the casting 

process (1/8" per foot), the mold was 

made slightly larger than the pattern 

ensuring that all panels, original and 

new, would be the same size. Vents 

and gates were created in the mold to 

allow the flow of molten iron and gas. 

Although the method of casting new 

panels was nearly identical to the historical process, the composition of the 

cast-iron was altered to improve the 

material's tensile strength. To produce 

what is referred to as ductile iron, the 

iron was combined with a slightly 

higher percentage of carbon (+/- 3.75% 

in the new cast-iron versus +/- 3.5% in 

the historical). Very small amounts of 

magnesium and graphite were also 

added to produce a material two to four 

times stronger than that of historical 

cast-iron. 

Following fabrication, the new panels were shipped to the contractor who 

set the new glass lenses and transported them to New York City for installation alongside the repaired panels (see 

figure 11). 

Reinstallation 

The reinstallation of the panels at 552-

554 Broadway was straightforward 

because the substructure that supported 

the vault lights and saddles had been 

reinforced with steel members approximately seven years earlier. Where 

leaking panels had led to the deterioration of the original stringers and support structure, the previous contractor 

shored up the substructure by replacing 

the deteriorated stringers with T-beams 

Figure II. Just prior to installation, each 

panel was lifted by hand from the back of a 

truck and stacked on the sidewalk. 

5 
Figure 12. During the installation, each panel was set onto the supporting 

T-beams that span the vault. A steel supporting girder, running perpendicular to the beams, is visible within the vault opening. 

Figure 13. The restored and reinstalled panels prior to repainting the saddles. Figure 14. The restored panels after work was completed. 

spaced beneath each joint between 

adjacent panels (seejigure 12). 

Additionally, newly cast frame sections 

were bolted together and installed 

beneath the sidewalk surface. As part 

of the current restoration, the contractor examined the substructure at 552-

554 Broadway and determined that the 

previously rebuilt assembly did not 

require additional strengthening or 

modification. 

To reinstall the panels, a bead of 

flexible polyurethane caulk was 

applied around the perimeter of the 

support frame. The panels were positioned on top of the sealant, in the 

same order they were set before 

removal, ensuring that the bolt holes 

would align (seejigure 13). Four 

stainless steel flat-headed machine 

screws secured each panel to its framework. A flexible foam backer rod was 

inserted into the seam around each 

panel filling much of the gap. The 

6 

same grout that was used to seal the 

glass lenses was also applied to the top 

of the backer rod to form the final surface seal. Again, excess grout was 

carefully cleared from the joint. The 

last step was to touch up paint on any 

area that was scratched during transportation or reinstallation. 

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 jigure 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. This work shows that proper 

installation techniques and periodic 

maintenance can ensure the long-term 

performance of vault lights. 

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 res

toration. 

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 manufac

-

turers. When historic panels are miss-

ing, new ones can be fabricated, utilizing the same methods used to cast 

ornamental iron features and replace-

ment 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. When part of a building 

rehabilitation, costs associated with the 

vault light work may be eligible for 

state or federal tax incentives. 

The project described here took 

eight weeks including removal and 

reinstallation. 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 feature frequently overlooked and 

under maintained. Considered beneficial for the way they manipulated light 

and improved dark, potentially usable space, vault lights were also a visual 

Concrete Vault Lights 

Although this publication focuses 

on cast-iron vault lights, it is also 

possible to replace deteriorated 

or even missing historic reinforced concrete vault lights. 

Beginning in the early 1900s, 

this type of installation supplanted cast-iron panels. When 

three existing concrete panels in 

the sidewalk in front of Smith 

Tower in Seattle, Washington, 

were damaged by a construction 

truck, owners turned to a local 

concrete precaster to replicate 

the panels. The two inch thick, 

4' x 9' panels dated to the first 

decade of the twentieth century 

and contained 180 Luxfer glass 

lights with saw-toothed prisms 

extending below. To cast new 

panels, measurements were first 

taken of the surviving panels 

and used to build a wood formwork (see figure a). Styrofoam 

cubes were set in the form to 

act as block outs for the square 

glass li

ghts. A quarter inch, 

twisted square, steel rod was 

embedded in the original panels 

to reinforce the concrete. To 

obtain even greater strength in 

the new panels, a grid of steel 

reinforcing bars and standard 4" 

x 4" wire mesh was secured 

between the styrofoam blocks. 

Then concrete was poured into 

the mold. After the concrete 

set, workers removed it from 

the form and dug out the styrofoam placeholders (see figure b). New 1-3/4" square by \" 

thick glass blocks with a pinkish tint to replicate the historic 

solarized lenses, were obtained 

from a local glass caster and set 

in the square voids with an 

epoxy. Then, the panels were 

transported to the building site 

and in

stalled with a backer rod 

and caulk (see figure c and d). 

Figure d. 

7 
complement to a building's entrance 

and facade. Today, whether severely 

deteriorated, buried under layers of 

asphalt or missing altogether, this feature need not be lost. 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. 

PROJECT DATA: 

Building: 

552-554 Broadway 

New York City, New York 

Project Date: 

2002 

Contractor: 

Rocco V. DeAngelo 

Antique Cast Iron, Inc. 

Cherry Valley, New York 

Replacement Glass Supplier: 

Blenko Glass Company 

Milton, West Virginia 

Replacement Panel Fabricator: 

Talladega Foundty and Machine 

Company 

Talladega, Alabama 

Cost: 

The total cost of the vault light rehabilitation project at 552-554 Broadway 

was approximately $70,000 or about 

$318 per square foot. Forty-five percent of this total was attributed to labor 

costs for sandblasting, hand cleaning, 

repainting, resetting glass lenses, grouting, touching up the panels, as well as 

welding the cracked or damaged panels 

and the two newly cast panels. Thirty 

percent of the total cost was for dismantling and reinstalling the panels, 

including transportation. The remaining twenty-five percent was for materials, primarily new glass lenses. This 

project did not include structural work, 

which would have added to the overall 

cost of the project. 

Photo of Bleecker Street station in 

"Vault Light History" sidebar is courtesy of New York Transit Museum 

Archives, Brooklyn, New York. 

Photos in "Concrete Vault Lights" 

sidebar are courtesy of Fred R. Beyers, 

Master Precaster Inc., Puyallup, 

Washington. 

All other photos by the authors unless 

noted. 

THIS PRESERVATION TECH NOTE was prepared by the 

National Park Service. Charles E. Fisher, Heritage 

Preservation Services, National Park Service, serves as the 

Technical Editor of the PRESERVATION TECH NOTES. 

Information on the 552-554 Broadway vault light project was 

generously provided by Rocco V. DeAngelo of Antique Cast 

Iron, Inc. Special thanks are extended to Elise Quasebarth of 

Higgins and Quasebarth, David M. Look at the Pacific Great 

Basin Support Office of the National Park Service, and Jo 

Ellen Hensley, John Sandor, Shannon Dodge and Sharon C. 

Park of the National Park Service's Heritage Preservation 

Services for their review and comments. Thanks also go to 

Alan Weiskopf of Perfido Weiskopf Architects. 

tural resources. All techniques and practices described herein 

conform to established National Park Service policies, procedures and standards. This Tech Note was prepared pursuant 

to the National Historic Preservation Act, which direct the 

Secretary of the Interior to develop and make available to 

government agencies and individuals information concerning 

professional methods and techniques for the preservation of 

historic properties. 

PRESERVATION TECH NOTES are designed to provide 

practical information on traditional practices and innovative 

techniques for successfully maintaining and preserving cul8 

Comments on the usefulness of this information are welcomed and should be addressed to PRESERVATION TECH 

NOTES, Technical Preservation Services, National Center for 

Cultural Resources, National Park Service, 1849 C Street, 

NW, (2255) Washington, DC 20240. 

ISSN: 0741-9023 PTN 47 November 2003