Many historic buildings are subject to deterioration from water penetration through the building envelope and into the building components. Unless the underlying structure is inspected and repaired concurrently with the failed building envelope systems, the structural components may continue to deteriorate, causing high maintenance costs, potentially difficult repairs, and sometimes unsafe conditions. To effectively address and respond to the discovered conditions, in-depth knowledge of historic, and sometimes archaic, construction components and systems is needed. This article demonstrates the importance of a comprehensive approach to building envelope and structural repairs to existing buildings.

Background
The Lyceum Theatre, located at 149 W. 45th Street in New York, is the oldest continuously operating, legitimate theater on Broadway. When the Beaux-Arts theater opened in 1903, it boasted the first cantilevered balcony on Broadway, which eliminated columns that obscured views from the orchestra level seats. The intimate, 922-seat theater is a transitional masonry structure; the theater has a steel-frame skeleton with perimeter steel framing embedded into the exterior, load-bearing masonry walls.

While most of the six-story building’s façade is composed of limestone-colored terra cotta, the first floor has a granite base with a limestone facing. Rising above the first floor’s undulating canopy and marquee are six terra cotta columns, which terminate in Corinthian capitals and support a massive entablature decorated with terra cotta theatrical masks. The entablature contains a shallow balcony with a balustrade. Three, one-story pedimented windows extend from the balcony to a secondary cornice that runs the full width of the façade below a slate mansard roof, which is framed with ornamental copper.

In 1974, the Lyceum was the first Broadway theater to be granted landmark status, and in 1987 the interior was also designated a New York City Landmark. Starting in 1981, a façade repair and restoration campaign was undertaken that included the replacement of terra cotta modillions below the cornice and the refurbishment of the original casement windows. In 1986, a new canopy and marquee were constructed over the main entrance, and secured back to the masonry façade using a series of tie-rods and cables. During recent repair and restoration work, undertaken to address a variety of building envelope issues, the contractor uncovered several localized areas of underlying structural deterioration that required repair.

As with many historic buildings, there are no existing construction drawings, and many of the methods and materials typical of the time period are outdated. Given that many repairs must incorporate modern means and materials, it is important to implement repairs that are compatible with the original fabric. In addition, the repairs must also maintain or improve the building’s durability while preserving its architectural appearance.

Water causes deterioration
Water penetration into building components and structure causes deterioration. When steel is exposed to both moisture and oxygen, the steel begins to corrode. Rust, the corrosion byproduct, can be up to 10 times the original steel’s volume. When the steel is encased in concrete, masonry, or terra cotta, the encasement constrains the volumetric change, creating expansive forces that cause distress in the surrounding material. This distress causes cracking, which allows for more water to penetrate and creates an autocatalytic cycle that accelerates the rate of deterioration.

Leakage-related problems are exacerbated in the winter months during cyclical freezing and thawing of water, a mechanism commonly referred to as "freeze-thaw." Because water expands when frozen, the expansive forces cause distress to the surrounding materials. Porous materials, such as masonry and concrete, can be especially susceptible to freeze-thaw damage.

At the Lyceum, the contractor uncovered leakage-related deterioration in several localized areas while making repairs to the building envelope. Cracks in concrete were found at the flat roof, which may have been the result of water leakage and freeze-thaw conditions. In addition, embedded structural steel had corroded at the mansard roof eave, the balcony, and at certain column bases, causing distress of the surrounding terra cotta. Each of these problems was addressed as encountered during construction.

Flat roof
Contractors began their building-envelope repairs at the roof, including replacement of the built-up roof, which had reached the end its useful life. However, when they removed the existing roof membrane, they found widespread delamination and cracking in the cinder concrete substrate as shown in Photo 1 below.

To better understand the construction and severity of the cinder concrete’s deterioration, we made exploratory openings in the deteriorated surface. Our openings revealed that the roof deck is composed of a thin layer of concrete, atop cinder concrete infill, over a flat-arch terra-cotta system that spans between steel beams (Additional A). The top flanges of the steel beams extend above the terra cotta. The cinder concrete infill extends above the top flanges and helps to fireproof the beams.

Cinder concrete is a mixture of cement, sand, and cinder aggregate. Cinder aggregate is the non-combustible byproduct from the combustion of coal or ash. Porous and cellular, cinder is lightweight compared to conventional stone aggregate, and its non-combustible properties make it a good constituent for concrete used as fireproofing. While cinder concrete was originally a good, lightweight material that provided fireproofing to the top beam flanges, the porous aggregate makes it susceptible to freeze-thaw damage when exposed to water and freezing temperatures.

Given that the thin layer of concrete above the cinder concrete was delaminated, and that the cinder concrete infill was loose and friable, both materials did not provide a suitable substrate for a new roof membrane. Complete removal of the cinder concrete would risk damaging the underlying terra-cotta, flat-arch structure. To complicate matters further, the layer of cinder concrete was slightly tapered, but it was not pitched at a minimum of 1/4-inch per foot slope, the commonly accepted pitch used to ensure adequate drainage. Increasing the pitch to 1/4-inch per foot slope would have significantly increased the concrete thickness and weight, even if lightweight concrete was used, and would have required beam strengthening, which is costly and disruptive. Consequently, the team chose a repair that would improve the roofing’s slope and durability without increasing the weight of the roof or significantly disrupting the existing structure.

Repair solution—The team removed the upper delaminated concrete layer and the friable concrete down to 1/2-inch below the top beam flange and installed metal decking transverse to the steel framing. To protect the exposed beam flanges, we applied a Tnemec coating, but this precluded welding of the metal deck. As a result, we fastened the deck using self-drilling screws. On top of the new steel deck, tapered insulation established the desired slope and provided the substrate for a new Kemper roof membrane.

Mansard roof
While the slate covering the mansard roof was in good condition, the surrounding ornamental trim, flashing, and gutters at the base of the mansard roof had deteriorated. One gutter ran just above the cornice at the base of the mansard. The deterioration of the gutter had allowed water to penetrate the masonry wall and reach the embedded steel beams. The expansive forces caused by the corrosion of the beams had pushed the terra cotta units away from the supporting masonry backup. During repairs made in the 1980s, steel pins were added to these terra cotta units to reattach them to the masonry backup.

During the current repairs, the gutter was scheduled for replacement and the terra cotta units pinned in the 1980s again required repair. With the removal of the terra cotta, gutter, and surrounding slate, the connection between the steel roof rafters and the spandrel angle was revealed. The design team observed corrosion at the rafter-to-spandrel connection, which prompted additional exploratory work to better understand the condition of the wide-flange roof joists located directly inboard of the dislodged terra cotta units.

Similar to the flat roof, the mansard roof is a terra cotta, flat-arch roof that spans to steel double-channel rafters. The channel rafters are connected to a spandrel angle, which spans continuously across the tops of wide-flange attic floor joists near their supported end. Riveted clip angles connect the rafters to the spandrel, and bolts connect the spandrels to floor joists. Hairpin bars pass through the web of each floor joist to anchor the masonry walls.

We probed the terra cotta and brick infill at each attic joist along the full length of the cornice to determine the extent of deterioration. Exploratory work revealed that the attic floor joist had suffered corrosion-induced loss of section, primarily in the web, at areas closest to the building exterior. This is understandable, as these are presumably the areas most exposed to moisture and oxygen. Areas embedded further into the brick wall were better protected from moisture and had little visible corrosion. Likewise, the steel rafters, which were embedded in the flat-arch terra cotta of the sloped roof, had little visible corrosion. At the riveted rafter-to-spandrel and bolted spandrel-to-joist connections, we found significant corrosion of the rivets, but the members and bolts were not significantly corroded. On the whole, the rivets and floor joist webs required remedial strengthening to reestablish adequate structural capacity.

Repair solution—The team designed supplemental web plates to reinforce the deteriorated attic joist webs, and welds to remediate the clip angles with deteriorated rivets. Because welding was not common for steel at the time of original construction, impurities in the steel’s chemical composition did not have the same limits as in today’s standards. Impurities can adversely affect weldability and the performance of welds, so before proceeding with construction, we required chemical analysis and testing of steel samples.

The chemical analysis revealed high levels of phosphorus in the building’s structural steel. To check for weldability, we directed in-situ bend tests. For each test, we welded a small steel plate tab to the existing structure with a one-sided fillet weld. We then used a hand-held hammer to bend each plate over at the weld. Our mock-up weld also provided the opportunity to visually inspect the weld for cracking or porosity. In this case, use of an E7018 electrode produced quality welds that deformed without fracture or separation from base metal, meaning welds could be used for the structural repairs.

Balcony
During repair of the balcony, workers uncovered embedded steel outriggers that support the cornice. The outriggers were corroded and had significant section loss as shown in Photo 2 (left). To reinstall the modillion blocks, significant cleaning, strengthening, and coating of the outriggers was needed. Instead, the outriggers were replaced in kind. Replacement framing was fabricated to match the original steel configuration, and a protective coating was applied to the steel before installation.

Column pedestals above the marquee
The terra cotta units exhibited localized cracking and delamination at the base of the colonnade pedestals. To investigate the cause of distress, the damaged portions of the terra cotta units and some loose brick infill were removed. We learned that the terra cotta and brick columns bear on steel shim beams, which rest on wide-flange beams that span between a pair of double-channel outriggers. Several shim beams were significantly corroded, had section loss, and required replacement; see Photo 3 (left). The expansive rust scale caused cracks and delamination at the weak pedestal edges.

The shim beams provide support for the columns that support the entablature and balcony. To remove and replace the shim beams, shoring the columns would be necessary, however; shoring is prohibitively expensive and disruptive. As an alternative, the team designed a carefully sequenced repair that entailed sequential load transfer from shim beams to newly placed concrete. Deteriorated concrete and fill material between each shim beam will be sequentially removed and replaced with concrete. Once the column is fully supported with concrete between the steel elements, the shim beams can be removed and additional concrete installed in lieu of new steel sections. By the end of the sequence, all existing concrete and shim beams will be removed and replaced with new concrete. To safeguard against future corrosion, all steel members will receive a Tnemec coating and sacrificial zinc anodes will be cast into the concrete encasement.

Lessons learned
While building envelopes are constructed to prevent water entry, it is not uncommon for older buildings to leak. Aging roof membranes, improper drainage, failure, or loss of material and cracks are all potential sources for water entry. Invariably, water penetration, unless quickly rectified, results in some form of damage to the building components and systems.

Structural systems are affected by corrosion of steel elements, such as embedded steel beams or reinforcing bars. The ensuing cracking and delamination in the encasing materials causes further steel corrosion by accelerating water leakage. Freeze-thaw cycling of water in encasing materials can also cause deterioration and further water penetration.

In general, when remedial repairs are made to restore the building envelope, it is important to inspect both the building envelope and underlying structural system for water damage to both systems. Façade or roof problems should not be repaired without fully understanding the type of structural systems, whether or not they are in need of repair, and whether or not the underlying damaging agent has been addressed. In addition to making exploratory openings, taking samples, and documenting existing conditions, comprehensive knowledge of historic construction and detailing, as well as modern building envelope and structural practices, is often required to fully understand the problem and provide effective solutions.

At the Lyceum Theatre, deterioration to the terra cotta façade, mansard roof drainage system, and aging flat-roof membrane were apparent by visual inspection alone, but the structural damage was not readily apparent. Exploratory openings, the removal of terra cotta units, and the removal of roofing membrane revealed deteriorated structural members and cinder concrete. While some of the structural repairs were unanticipated, the presence of corroded structural elements was not surprising. The ensuing repairs not only rectified the underlying problems, but also minimized further deterioration of the building envelope and structural elements. Through recent structural remediation and building envelope repairs, the service life of this historic landmark has been extended, allowing the oldest continuously operating theater on Broadway to entertain people for years to come.

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Design and construction team
Project name: Lyceum Theatre
Owner: The Shubert Organization, New York
Structural engineer and architect: Simpson Gumpertz & Heger Inc., New York
Contractor: Yates Restoration, New York
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Senior Staff Engineer R. Scott Silvester, P.E.; Senior Engineer Rebecca Melton, P.E.; Senior Project Manager Diane Kaese, R.A; and Principal Milan Vatovec, P.E., are all employed in the New York office of Simpson Gumpertz & Heger. They can be reached at rssilvester@sgh.com, ramelton@sgh.com, dskaese@sgh.com, and mvatovec@sgh.com, respectively.

Historic photo is courtsey of The Shubert Archive.