Written by: Amanda Brown, Bennett Preservation Engineering PC
Drayton Hall is a National Historic Landmark located on the Ashley River in Charleston, South Carolina.
This 1740s masonry structure, owned by the National Trust for Historic Preservation and operated by the Drayton Hall Preservation Trust, is considered the nation’s finest and earliest example of Palladian architecture. When the National Trust acquired Drayton Hall in the 1970s, the decision was made to “preserve” the site in order to protect its authentic, multi-century history rather than restoring the structure to a specific period.
For more than 250 years, Drayton Hall has stood witness to the American South. Among the best and most complete examples of Southern colonial life open to the public today, the property holds a vital educational responsibility. The mission of the Drayton Hall Preservation Trust is to foster “a deeper understanding of colonial America and the evolution of life in the South by discovering, researching, conserving, and interpreting the history, context, and culture of Drayton Hall.”
Like so many details at Drayton Hall, the mahogany staircase is original to the building, and unique among houses of the period. Crafted largely from mahogany and then painted a striking vermillion color, the impressive staircase survives largely intact, the only notable alterations being replacement newel posts and balusters near the foot of the stairs. While the staircase looks much the same as it did in the mid-eighteenth century, its use has changed dramatically. Once tread by individuals associated with the household, the staircase now carries thousands of visitors each year, bringing new stresses for which it wasn’t designed.
As a result of a structural assessment and visitorship capacity study, Bennett Preservation Engineering found the stresses in the staircase to be serious enough to recommend structural improvements. The staircases leading from the first to the second floor are symmetrical and, if loaded symmetrically, act as if they were two sides of an arch. However, the stairs are generally not loaded symmetrically and, if the upper landing were to move significantly, there would have been the possibility of a “snap-through” failure. Load capacity computations showed that the connections at the ends of the stringers had reduced capacity, despite having already been upgraded once. In addition, the handrails had relatively low capacity compared to that required by current code and there was concern that if a visitor should accidentally fall against the handrail, the risk of the handrail failing was significant. Hence, if you have climbed the mahogany staircase at Drayton Hall prior to this preservation project, you likely heard what the staff at Drayton Hall dubbed, “the safety speech.” All visitors to the second floor were instructed to ascend single file, with three stairs between one another, and with a light touch on the handrail.
In November 2021, a team from Richard Marks Restorations began the much-anticipated Stair Hall project with the goal of significantly increasing both the gravity and lateral load capacities of the stair systems, with minimal impact to the historic fabric and to the visitor experience.
Temporary jack post columns were installed in the cellar to support the joists of the Stair Hall above while the undersized and overstressed girders were being replaced. The jacks were installed on custom sand boxes designed to distribute the loads they carried, to create a level surface and to protect the stone floor below. The old girders, installed in 1967, were removed and the exterior masonry wall of the structure was prepared to receive the new girders. The new girders, composed of a stronger builtup LVL, were designed to match the depth of the existing girders. A new stronger connection was formed between the girders and the historic joists. At the exterior masonry wall, the girders were placed in custom copper boots to protect the ends of the wooden members from moisture and accelerated deterioration.
Upstairs in the Stair Hall, each individual component of the staircase was labeled with an orange tag and then noted on a diagram to ensure that it would be reassembled in its original location. The pieces were protected and stored while the underlying structure of the stairs was strengthened. The original historic framing was all maintained in place, while new wooden sisters were installed at overstressed stringers and headers. None of the original framing was cut, but instead the new sisters were “scored” to match the unique stepped shape of the stair stringers.
The connections of the stringers to the landing beams were strengthened with hidden custom steel brackets and angles, installed to add strength and stability to the existing system. A templated mockup of every steel angle was created to ensure that the new connections would fit within the stair system and remain hidden from view. Finally, hidden tie rods and plates were installed within the uppermost cantilevered landing to address the concern of a “snap-through” failure.
In addition to strengthening the framing of the staircases, Bennett Preservation Engineering designed hidden strengthening mechanisms for the handrail system to better protect visitors against failure. The connections of the handrails to the posts were strengthened with hidden screws or bronze plates, and the connections of the posts to the landings were strengthened with clips and screws. Wooden plugs, matching the existing wood type, grain direction and finish, were installed at all screw holes.
Once the strengthening was complete, each piece of the mahogany staircase was returned to its
original location, and the staircase was reassembled and opened to visitors once again. The result is a staircase that is much stronger, but which retains most of its original material and, unless you are crawling underneath it, looks the same as it has for generations.
This project exemplifies Drayton Hall’s approach to preservation—protecting its resources for the future while conserving as much as possible from the past. With the project now complete, Drayton Hall has reopened the second floor for interpreter led tours.