Glass structures in historic milieux

In order to achieve acoustic isolation for the intimate Lady Chapel worship space, MBB’s design solution centers on a glass enclosure filling the 14-m (48-ft) high arch.
In order to achieve acoustic isolation for the intimate Lady Chapel worship space, MBB’s design solution centers on a glass enclosure filling the 14-m (48-ft) high arch.

This design solution, which could be considered for a range of historic settings, required careful planning and significant consideration of preservation logistics. In this case, the doorframe’s limestone surround was removed, cut down 127 mm (5 in.), and reinstalled to accommodate the channels.

The work of setting the glass entry doors into place was made even more complicated by the need to keep the cathedral open to visitors and worshippers throughout the process. Intelligent and precise coordination and scheduling was instrumental to success. The project team conducted preparation work during the day by simply cordoning off the area around the entry doorframe, maintaining public access to the cathedral’s interior. Installation work took place at night and in the early morning. Working with an architectural metal and glass fabricator and installer, Structure Tone orchestrated closing off a portion of Fifth Avenue so the glass assemblies could be delivered and set into their pockets.

 New motorized sliding glass pocket doors welcome visitors to the cathedral entrance, allowing the original bronze doors to remain open while minimizing heat and air-conditioning loss. Photos © Elizabeth Felicella/Esto

New motorized sliding glass pocket doors welcome visitors to the cathedral entrance, allowing the original bronze doors to remain open while minimizing heat and air-conditioning loss.
Photos © Elizabeth Felicella/Esto

A minimalist enclosure and technical challenges encountered

In addition to improving the cathedral entry, archdiocese leaders sought to enhance the functionality of interior worship spaces. Over time, the popularity of St. Patrick’s Cathedral and the sheer number of daily visitors had acutely impacted the ability of its Lady Chapel, an addition on the east side of the cathedral built in the early 1900s, to serve as a quiet, intimate space. Responding to the changing needs of worshippers and the visiting public required creating an enclosure that could provide acoustic separation between the main cathedral areas and the chapel itself. Any intervention also had to preserve the original character of the spaces and allow them to remain quiet while still also feeling contiguous and consistent with the rest of the structure’s architecture.

As with the glass entry doors, for the Lady Chapel enclosure, the project team was committed to a design approach that complemented and worked
in concert with the existing aesthetic. A carefully detailed glass structure again proved to be the most sensitive solution. Employing an iterative design process in collaboration with the glass fabricator, the architecture team gradually reduced this separation to its essentials. Early schemes featured substantial framing with steel beams and wood tracery responding to the adjacent cathedral space. As the design and engineering developed, the team formulated a solution that would eliminate excess framing material while creating an all-glass assembly.

During a six-week installation process, the glass enclosure work was staged on a side street to protect the structure and interior spaces. Photo © Murphy Burnham & Buttrick Architects
During a six-week installation process, the glass enclosure work was staged on a side street to protect the structure and interior spaces.
Photo © Murphy Burnham & Buttrick Architects

A high level of technological and engineering sophistication was required to achieve the resulting liminal gesture and its required level of performance, from the design of the installations to the suitable materials and detailing. Three 38-mm (1 ½-in.) thick, triple-ply laminated glass panels—each weighing up to 2267 kg (5000 lb) and entirely supported by a horizontal, 101-mm (4-in.) wide, 7-m (24-ft) long laminated glass beam—now fill the Lady Chapel’s 14-m (48-ft) high arch. The installation presents a light and effortless sensibility, yet is a significant presence. Most importantly, it improves facility performance without negatively impacting the surrounding architecture or creating any visual barrier around the Lady Chapel.

While St. Patrick’s Cathedral is an iconic landmark and destination for visitors, it is also a thriving house of worship. There are up to 18 said masses performed each day and 150 weddings each year. With an acoustically separated chapel, the cathedral can accommodate simultaneous ceremonies (e.g. worship, weddings, funerals) in the chapel and the nave. Perhaps more importantly, the Lady Chapel was conceived as a sanctuary within a sanctuary—a place for quiet prayer and devotion. In a building that now sees more than 5 million visitors each year, creating a space of quiet refuge is more vital than ever to the cathedral’s mission as a spiritual home.

With transparency as a crucial element, this glass structure sits in a minimal and carefully detailed bronze frame. Aiming for the highest possible level of visual integration with the cathedral, the project team treated the bronze to match the historic architecture. Acid treatment brought the metal from a bright gloss to a darker finish, calibrated to match the historic bronze doors at the front of the cathedral. The frame itself is entirely machine fabricated, but the acid treatment had to be hand applied. A traditional crafts specialist sponged the acid on from a bucket, then washed it back off after a prescribed time period to achieve the desired finish.

To create a pocket for the motorized glass entry doors to slide into the existing structure, the project team shifted the interior wall by 101 mm (4 in.) and removed some of the stone entirely.
To create a pocket for the motorized glass entry doors to slide into the existing structure, the project team shifted the interior wall by 101 mm (4 in.) and removed some of the stone entirely.

The skill of the project team’s various tradespeople and craftspeople allowed the design team to go above and beyond, adding small touches that would bring outsized value. For example, using custom door hardware allowed MBB’s team to design a quatrefoil seal—the symbol of St. Patrick’s Cathedral—for the inner side of the bronze door pulls on
the glass doors into the Lady Chapel enclosure. This attention to detail in deference to the historic architecture was important for cathedral leaders. A key moment in the design and planning process took place on a trip to Germany, where archdiocese representatives became convinced of the appropriateness of an all-glass intervention after seeing a mockup of the assembly in the glass manufacturer’s workshop.

Skilled collaborators, advanced technology for complex site conditions

Before any glass even came into the cathedral, the project team had to design and install the bronze frame to fit perfectly into the Lady Chapel’s historic plaster arch, marble columns, and floor. This was an exacting process, as all the existing building components are irregularly shaped. To document the structure, the project team engaged digital surveyor Hypsometric to undertake a full 3D scan of all interfaces. Using a terrestrial light detection and ranging (LIDAR) scanner to create a virtual model of the building components enabled the project team to form and shape the structure to follow the irregularities of the historic architecture, but remain regularized enough to create clean visual lines. The historic columns presented a particular challenge to the scanning tools, as subsurface refraction within the marble returned inaccurate data. The team compensated by covering the columns with painter’s tape for the scan, then adjusting for the thickness of the tape in the final point-cloud model.

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