Using Modern Building Techniques to Emulate Old World Charm: Charleston’s Jasper Building

In October of 1949, The Sergeant Jasper Apartments opened its doors to the public, heralding “An adventure in Modern Living.” In operation for six decades, the original building shuttered its doors in 2014.  Though preliminary redevelopment discussions between the local developer, The Beach Company, the City of Charleston, and neighborhood groups started in 2010 amidst a major economic downturn, it was another four years before the project arrived on the drafting boards of LS3P.  After six major design schemes and one court ruling, the final design was approved by the city’s Design Review Board in June of 2017.  Groundbreaking for the project followed in August of 2018, with project completion anticipated for early 2021.

The new 12-story mixed use project includes 219 rental residential units, approximately 74,500 SF of Class A office space (including the headquarters of The Beach Company), 41,390 SF of amenity space (including a fifth floor open air pool deck and enclosed fitness areas), and roughly 25,500 SF of retail space on the ground floor.  The stated program also wraps and encapsulates a four-story, 524-space parking garage.

Historic Neighborhood, Strong Opinions

The Jasper building replaces an earlier 15-story, post-war era multi-family structure situated in the Harleston Village neighborhood of downtown Charleston.  The site has commanding views to both the Ashley River (to the west) and the Charleston Harbor (to the east), with immediate neighbors being Colonial Lake, Moultrie Park, and the South of Broad historical residential neighborhood.  Given this context, the new building needed to complement its adjacent neighbors.

The design process was nothing short of contentious, as public sentiment was against a high-rise development in this part of Charleston – even though an existing 15-story building stood on the site for 65 years prior.  Starting in February 2015, LS3P produced six designs over a three-year span (“PUD 3X,” “Building in the Park,” “Building in the Park Modified,” “Plan A,” and a separate fully permitted drawing package to renovate the existing building and the final design as realized).  During this time, a court ruling was handed down, permitting The Beach Company to proceed with developing their land after reaching an impasse with the city.

Architectural Precast: An Innovative Solution

Designing an appropriate façade in this particular context created challenges that required an innovative solution. The precast concrete façade strategy required a series of meetings to educate the community and local review board members alike, as various stakeholder groups were initially skeptical about the use of a modern building system which had not yet been used in a historical Charleston context. The use of thin brick-clad precast panels was a novel approach for the area.

Say “precast concrete panels” and most individuals think of utilitarian parking garages with flat, nondescript detail.  These buildings typically employ long-span structural precast panels due to the economy of the system.  Structural precast typically uses post-tensioned reinforcing.

Architectural precast, on the other hand, uses a high-density concrete mix (5000 psi) and conventional rebar and offers more flexibility in profile and detail at the expense of span.  Typical panel thickness is 8” with a minimum panel thickness of 5”.   Panel size is limited to highway transportation constraints as well as crane picking capacities.  Joints between panels are typically ¾” and need to be planned with the fabricator to avoid telegraphing the various individual precast pieces.  This is particularly important when designing buildings inspired by historic building precedents.

Upon arriving to the site, panels are erected using either a tower crane from above or walking/ crawler cranes from the ground.  Anchors embedded in the back of the panel are set, adjusted, and welded to the receiving anchors along the building’s perimeter edge of slab.  Installation of individual pieces is a well-choregraphed process between ground crew, crane operator and receiving crew on the upper floors and occurs in a sequential manner.

Why Architectural Precast?

Production of precast concrete panels offers greater quality control and speed over conventional hand-laid masonry veneer, as the process occurs in a controlled indoor environment negating any weather impact.  Large sections of the building envelope can be installed at once without the need for scaffolding, thereby expediting the dry-in time of the building.  This contributes to a shortened construction schedule and, in turn, overall cost savings from less construction general condition fees.

The use of architectural precast also allows detailing to exceed code-related masonry corbeling limitations, as the structural capacities of concrete and reinforcing combined surpass masonry.  This is critical when trying to produce a level of authenticity when emulating historic brick work.

Furthermore, the precast concrete with the proper aggregate, design mix, and surface prep can be left exposed to simulate dressed stone.  This eliminates further material costs as well as decreases the number of joints between dissimilar materials, thereby improving the effectiveness of the building envelope as a weather-resistive barrier.

Designing the Jasper Facades

A brick-clad building was originally proposed to mesh with the larger buildings in the surrounding area, but with the overall building height and scarcity of qualified skilled labor locally, ensuring consistent craftmanship would be a challenge.  Compounding the issue was the potential for high flood waters 4’-0” above the finish floor elevation at the ground floor level.

The use of precast concrete panels with integrally cast thin brick veneer allowed the design team to recreate the historical detail and charm to match the surrounding Charleston downtown. The design team chose tumbled thin brick to better simulate the varied texture associated with hand-laid masonry veneer.  The softened edges of the brick also added the weathered and timeworn appearance typical of Charleston’s masonry buildings.

Exposed precast concrete was also successful in simulating dressed limestone in both color and texture.  Decorative cornices, medallions, and pilasters rendered in similar material added another level of historic detail and sophistication.

Additionally, the robustness of the system enabled the design team to utilize the ground floor panels as a building flood-proofing component, as the site is 4’-0’ below the design flood level.  At the upper residential floors, the 8” thick panels also contributed to improved interior unit acoustics.

Coordination and Communication

Working closely with product reps is essential for precast construction, as the panelization requires both technical and engineering input from the fabricator.  It is best if this occurs earlier in the design documentation process (ideally in design development) so location and size of joints can be determined.  Given that Charleston is in a high seismic zone (Site Class D), the seismic joint was 2-1/4” wide.  Fortunately, the design team was able to work with GATE, the fabricator, to locate the joint at inner corners of the building along with some special window details.  It should also be noted the developer financed this upfront construction cost separately from the architect and consultant fees, but this also streamlined the construction submittal review process as all detail conditions could be worked out and documented.

Mock-ups as a Key Design Tool:

Initial mock-up panels were supplied by two separate fabricators competing for the job.  These panels not only showcased their craftsmanship and technical skills, but also served as exhibits to educate the members of the local Design Review Board.  Ultimately won by GATE Precast out of Oxford, North Carolina, the next round of mock-ups involved determining brick color and texture selection as well as precast design mix.

After creating four separate 4’-0” x 4’-0” panels with various bricks and precast colors, the selections were narrowed to two brick colors, one for the field brick of the office and residential tower and the other for the garage.  The design team also selected the exposed precast color that best simulated limestone.  The brick color for the office and residential tower led to further exploration, resulting in a special blend from Belden Brick.

Once these color selections were finalized and the brick selections passed PCI standards for freeze/ thaw cycles and pull tests, GATE fabricated four panels representative of the building facades and associated details.  The average size of the panels measured 8’-0” wide x 15’-0” tall and cost the developer an estimated $250,000.00 (including all mock-up materials and installation labor).

The local Design Review Board approved the mock-up panels, but not without testing the capabilities of the fabricator on field repairs.  As part of the review, Board members took a hammer to both portions of the exposed precast and thin brick to simulate damage during field install.  GATE Precast was able to repair the damage expertly, to the satisfaction of the Board and allowed the general contractor to move forward.  All said, the length of time from fabricator selection to final Board approval of the mock-ups took nearly two years (April 2017 to March 2019).

A New Approach and a Viable Long-Term Design Strategy

The success of the architectural precast strategy demonstrates that this system is an advantageous option for new buildings in historic contexts. In addition to the ability to create architectural elements which complement and enhance the built environment, architectural precast can reduce cost and accelerate construction. The ability to install the system without scaffolding creates cost and time savings, and the process reduces debris- both solid and air-borne- on site, minimizing disruptions to the neighborhood during construction over conventional hand-laid brick veneer.