Precision demolition in the Big Apple

by Jeff Winke

It sounds contradictory to talk about “precision demolition.” But think about removing a building from a tightly packed urban area and precision demolition or dismantling is exactly what is needed. The idea is to remove a single structure, not an entire block. Clearly, precise workmanship is required.

Enter CNY Group. Headquartered in Manhattan, CNY Group is a construction management firm that has overseen the precision demolition of a number of buildings from the densely packed New York City cityscape.

“About seven percent of our business is managing building demolitions,” stated Ken Colao, president and co-founder of CNY Group. “Our core competency includes large-scale residential, commercial, lodging and mixed-use construction; institutional, retail and interior construction, as well as building demolition. All of our large-scale work in New York involves demolition of some sort, and we usually plan and manage this part of the project.”

Here are three demo projects that showcase CNY Group’s demo project management capabilities.

701 Seventh Avenue, NYC

CNY planned and managed a delicate, and complicated demolition of an existing theater building built in 1904, and the adjacent bar/restaurant. The site, 20 Times Square, was to become the future home to the Marriott Edition and the NFL/Cirque du Solei. The building is the first high-rise to be built in Times Square in over 20 years.

First, the existing buildings were abated for all hazardous materials. Then, the scheduled demolition occurred in several phases.

“Once the permit for structural demolition was received, the first phase was soft demolition, where all architectural elements and exposed structural slabs, masonry and concrete walls, and encased columns were removed,” Colao said. “An updated version of a 3-D laser scan was completed and all the data was provided to the engineers and architects on the project and uploaded for a more complete understanding.”

The existing structural framing was often found to be undocumented or completely missing. As a result, the building had to be completely shored and structurally braced.

Demolition of the theater building started at an upper floor and included the removal of the central core of the building. One bay of the steel frame building at the perimeter corner on Seventh Avenue to the southeast corner on 47th Street was retained in order to help the demolition process.

The existing steel floor levels within this “L” corner were retained and were incorporated into the new structural framing that supports a new girder and truss platform above. Parts of the structure were not stable and had to be re-shored and re-braced, almost on an ongoing basis, as new conditions were uncovered. There was an extensive shoring and bracing plan developed by CNY, and the shoring and bracing engineer and coordinated with the structural engineer to stabilize much of the existing building.

Demolition involved constant coordination with the engineers from Howard Shapiro & Associates and engineer of record Severud Associates, due to unforeseen conditions relating to the theater being a structurally modified building. There was a need for extensive shoring and bracing of existing building framing, and coordination with new structural steel framing and truss system that was to be integrated and literally “stitched together.”

Certain elements of the building were required to be demolished to install temporary grillage, trusses, caps and caissons below to support the “L” structure above. Wind bracing on the upper floors were required to be completed prior to removal of brick walls on the interior and exterior.

“Exterior walls were required to be removed to allow us to erect the grillage and trusses on the ground floor,” stated Colao. “Ground floor slabs were required to be partially removed to fit the drill rig in the cellar level to drill the temporary caissons. Once temporary shoring, grillage, trusses, and pile caps were complete, we engaged the grillage and loading the temporary system, which allowed us to begin removal of the exterior columns. This also allowed us to start excavation for foundation and underpinning.”

Brooklyn-based Breeze Demolition was the demolition subcontractor on the 701 Seventh Avenue project.

Tammany Hall, NYC

Tammany Hall is a landmarked building in a high profile, congested area in New York City. Sandwiched between other closely spaced buildings, the CNY Group needed to interact with the tenants of the adjoining buildings, who needed to continue living and working with minimum impact during the demolition process.

“For this project, we are maintaining two historic facades and building a new superstructure behind the façade that will serve as high-end commercial space,” Colao said.

The exterior brick and stonework façade is landmarked and in the midst of a significant façade stabilization. CNY will remove the structure that previously held the façade and will build a new, more efficient structure to replace it. The two facades are being braced onsite with vertical towers placed outboard of the façade and will be reattached to the new superstructure after it is built. These building facades are at the corner of Park Avenue South and 17th Street on Union Square.

The secondary steel frame tying in the towers was designed to hold the facades fully stable while the old structure was removed. After the historic facades are attached to the new building, the temporary steel frame will be removed.

“During demolition, we must assure safety for the workers and the public,” Colao said. “We supervise a properly engineered sequence of removal to maintain a safe worksite at all time. In this case, we also had to address large, early 20th century trusses that had to be taken down in a controlled manner.”

Woolworth Residences, NYC

CNY is managing the extraordinary conversion of the historic Woolworth Building’s top 30 floors into 33 luxury, high-end residential condominiums, including a single five level townhome within the pinnacle at the top of the building.

Work at this 792-foot tall, National Historic Landmark involved restoration of the façade, gut renovation and structural reconstruction of core elevator shafts and stairwells from floors 29 through 58; shaft space on the second through 28th floors, and new ground floor entrance and lobby, cellars, and sub-cellar amenities.

The renovation includes approximately 110,000 square feet (net) of condominium residences; completely new mechanical-electrical-plumbing (MEP) infrastructure; two designated residential elevators and ground floor lobby; amenity space in the sub levels which houses the restored Woolworth pool and a wine cellar; lounge on the 29th floor; and a gym on the 30th floor.

Designed by famed architect Cass Gilbert, the Woolworth Building was the world’s tallest building, when constructed in 1913.

The projects outlined above give a flavor of the types of demolition projects that the CNY Group manages. The contractors who complete the demo work for CNY are screened and prequalified through a process CNY describes as rigorous before they are eligible to be hired for work. The management firm looks for contractors with proven experience, successfully completing similar, large demolition projects.

CNY identified five key challenges with a building demolition project in a congested urban area:

  • Make sure there is a well thought out and well-engineered plan for dismantling the structure and removal of debris. A logistics plan, controlled access, safety plan and in certain cases, verification and certification of structural integrity are prerequisites to starting work. It is important to have an experienced contractor to execute the work, to know how it should be done safely and in a controlled manner. Temporary structures built with falsework, now need to have an equally controlled means of being removed.
  • Conduct extensive probing, preconstruction surveys and a structural integrity review of all adjacent properties. Understand that older buildings, over time, often shift or lean against the neighboring property earmarked to be demolished.
  • Adjoining properties and neighbors must be protected from the forces released during demolition, so that they don’t damage buildings that were previously attached to it. Investigate and probe for party wall construction or no foundation of adjacent properties. There is also the issue of controlling the noise and dust during the demolition.
  • Site logistics is also key since there is a need for an efficient flow of heavy equipment and trucks in and out of the work site. This is a common urban issue. CNY prefers that its subs all own their own equipment. On the 20 Times Square and Tammany Hall demo projects, for instance, there were large active hotels opposite the site so, deliveries, demolition waste removal, and garbage pickups needed to be coordinated with the neighbor hotels’ schedule. There is often a need to coexist with the neighbors.
  • And last, but not least there is likely the need for diligent monitoring of means and methods and its impact, and communication and coordination with other nearby construction projects. Cities are alive with activity.

When Ken Colao was asked to reflect on his more than 35 years of experience, which includes having completed more than $3.8 billion worth of construction in the commercial, hospitality, residential, institutional and government market sectors, both domestically and internationally, as well as his extensive precision demolition work…he was asked what’s the one demolition project in a tight, congested area he remembers most? What makes it stick out?

“The 701 Seventh Avenue demolition project right in the heart of Times Square was an incredible challenge and is a project that I’m proud of the work we did,” Colao concluded. “It involved suspending a single bay, 10-story, partially demolished structure over three cellar levels and subgrade demolition and rock excavation to exacting tolerances without interfering with the neighboring 42nd Street Subway structure. The work needed to be exacting and I’m proud to say we were on point throughout the duration of the project and accomplished precisely what we set out to do!’