34 South 11th Street East Market - Office and Retail Building Renovation
The second phase of the nearly $250-million revitalization of a four-block site in downtown Philadelphia, called the East Market project, focuses on re-building and renovating a warehouse building that will be clad with architectural precast concrete panels.
The eight-story 34 South 11th Street building requires stripping the entire existing deteriorated façade and replacing it with architectural insulated precast concrete panels. The panels will help the new facility, which will offer retail and office space, project a turn-of-the-century industrial aesthetic.
Adjoining portions of the East Market project include construction of a 17-story tower comprising two stories of retail with the rest devoted to apartments. This building also will feature architectural precast concrete panels embedded with terra cotta, along with other details made of precast concrete. The panels will be modulated in texture and color to achieve a distinctive, complementary look to the renovated building underway, says Michael Prifti, principal at BLT Architects.
“We’re pulling a lot of plays out of the precast concrete playbook for the 34 South 11th Street project,” Prifti says. “A variety of techniques are being used in a variety of ways to achieve all of the owners’ goals.”
On the warehouse renovation, precast concrete panels were chosen for their energy efficiency, design flexibility, and aesthetic capabilities, Prifti says. “Our intent with the precast concrete system is to create an appearance that provides a metallic feel, in a deliberate attempt to replicate a turn-of-the-century industrial architectural style.”
To achieve this, the existing façade, featuring brick and terra-cotta tile on its public face, is being totally removed. “The façade had deteriorated to the point that it was unable to be supported,” says Prifti. The original 1916-era framing system then will be modified to allow insulated precast concrete panels to clad the renovated building.
“The frame was a mixed bag,” explains Kyle Kernozek, an associate and project manager at BLT Architects. “A significant portion of the existing slab edges require repair, much of the rest requires minimal modifications, and some portions could be used as it was.” Those portions had housed mammoth freight elevators along the perimeter, leaving blank portions in the façade that could be filled in easily to provide purchase for the precast concrete panels to be connected column to column with clips.
The original brick façade was supported by steel angles, face mounted to the structural frame. These steel lintels had rotted out and damaged the slab behind, eliminating a uniform edge to support the new panels. The design team worked with Coreslab Structures (CONN) Inc. on a design-assist basis to create efficient panel sizes and insulation thicknesses, and then determined the weight and crane sizes that would be needed. Remedial design work then was done to create a sufficiently sound slab edge to carry the weight of the intermediate panels.
All of the panels were designed to be connected slightly outside of the column line, providing additional flexibility for interior fit out. “The panels have short connections, as some were set into the precast concrete to create notches so we could maintain their relationship to the top of the slab,” Kernozek explains. Welded joints also will be used on some panels where the curbs are too tight and the window walls come down to the top of the curb.
The 11-inch-thick panels feature 4 inches of IsoMASS insulation, providing a material R-value of 24.8 for the insulation alone. The insulation is sandwiched between an interior 4-inch wythe of concrete and a 3-inch exterior wythe. The panels also include 3-inch finned projections integral to formed casting. Two dark finishes were used, a light gray base color and a deep “charcoal” that was achieved with a stain. A very smooth, light sandblast texture was provided to help replicate a metallic appearance.
The panels are complemented by extruded-aluminum windows and an elegant glass storefront for the first floor of retail, which will include an organic grocery, restaurant, and several smaller stores. The lobby to the office spaces above also will be built into this space.
The construction site is hemmed in by downtown streets, including two privately owned narrow streets on the sides, as well as an adjacent parking structure. The precast panels will be fit around an existing ramp on the parking structure, with a five-story high, two-bay wide hole left in the panels to allow it to remain operational. Once the balance of future construction is complete, matching panels will fill this hole. “It will be relatively easy to pop the panels into this space at the end,” says Prifti. “It will be the precaster’s responsibility to ensure they perfectly match the appearance of the others.”
Architectural Precast Elements:
• 3 inches of polyisocyanurate insulation embedded in 11-inch panels.
• A very smooth, light sandblast texture was provided to help replicate a metallic appearance.