In-depth Study of the Dismantling and Reconstruction of a Century-Old Stained Glass Laylight — STRATA Architecture + Preservation

"The Great Window” at the Missouri State Capitol, which is more than a century old, is a keystone architectural element of the building that houses the seat of government.

It’s one of numerous projects that STRATA Architecture + Preservation has undertaken at the Capitol since 2010.

“It is one of the largest projects we have undertaken at the Capitol—if not the largest,” says firm Vice President Trudy Faulkner, AIA LEED AP, adding that the restoration of the press gallery in the building’s Senate chamber and the Legislative Library restoration were more extensive.

The stained-glass laylight, which is under the largest skylight in the 1917 building designed by Tracy and Swartwout, is suspended 60 feet above a two-story grand stair at the Capitol’s south entrance, a placement, Faulkner says, that “provides a moment of awe upon entering the building while looking towards the central rotunda while ascending the stair.”

Designed and fabricated by New York-based Herman T. Schladermundt and installed in 1921, the laylight contains 1,225 square feet of stained glass in 56 leaded panels that contain 26,500 individual pieces of glass.

“The artistry of the laylight stands out,” Faulkner says. “The level of quality and complexity is incredible. Each piece of glass is textured, and a stunning piece of artwork in itself. You would be hard-pressed to find anything comparable in the United States.

By the time STRATA Architecture + Preservation started the project, the laylight, which has an appraised replacement cost of $17.3 million, had deteriorated sections that so compromised the use of the staircase below, where a prime portion of visitor tours occur, that it had to be closed off for fear of falling glass.

Deciding to restore the laylight wasn’t as easy as it sounded. The state didn’t have the budget to erect scaffolding for STRATA Architecture + Preservation merely to assess the laylight’s condition, so the firm came up with a novel idea: Let drones take an up-close look at things.

“It still wasn’t as good as seeing and touching the laylight up-close, but it did give us more insight than just using binoculars from two stories away,” Faulkner says, adding that that information was combined with visual observations and high-resolution photography.

The team, which included glass artisans from Judson Studios, stained-glass conservator Julie L. Sloan and structural engineers from Bob D. Campbell & Co., decided that it was best to remove the stained-glass panels for repair and restoration and replace them with frosted polycarbonate while the work was in progress.

“It took four to five people to remove each panel,” Faulkner says, adding that archival rubbings were made of each piece of glass to ensure proper placement during reinstallation and to provide a record of what was in place before removal.

“Five vans were used to transport the panels,” she says. “Because of their high value, insurance coverage would not allow them all in one van.”

During the assessment, which was supplemented with 3D laser scanning using mesh overlays, photogrammetry and deformation analysis, it was determined that there were two main failures in the laylight.

The primary structure was deflecting because of the weight of the glass, age, thermal variations and an inherent design flaw where the arched structural ribs were interrupted to allow for the center oculus.

The secondary and tertiary framing of the individual panels was failing due to deflection from insufficient support – an issue that arose from the original fabrication suspending the stained glass above rather than supporting it from below. 

These issues were exacerbated by the fact that the lead came, sourced right after World War I when metals were scarce, was subpar.

To create a more stable, long-lasting structure, the team replaced the lead came, shifted the support bars from on top of the panels to below and added seismic clips and a new under saddle detail that doesn’t add weight and allows individual panels to be removed for maintenance.

The team also created a U-shaped carriage anchor that supports the secondary framing from below. More than 300 of the seismic clips in five to six configurations were used.

The carriage anchors were affixed to the primary steel with set screw bolts, and neoprene tape was inserted between the steel and glass panels as a spacer to minimize stress or friction.

U-shaped anchor clips were also placed over the primary steel framing and anchored in place to provide tie downs from the glass panels in the case of a seismic event.

Each piece of glass had to be cleaned at least two to three times to remove a century of grime buildup.

The modifications to the historic design, in addition to the tinning of both sides of the glass panels that provide a stiffened assembly with solder, Faulkner says, “make the glass panels strong enough to last another 100 years, factoring in increased seismic requirements, and still maintain a historically appropriate appearance. The finished work provides a cleaner appearance, casting fewer shadows on the glass and thus enhancing the original historic intent of the art while drastically improving the structure of the laylight.” TB