Traditional Building Portfolio
Palladio Awards

Project: Residence, Chester County, PA

Architect: Peter Zimmerman Architects, Berwyn, PA; Peter H. Zimmerman, AIA, principal; William H. Johnson III, AIA, project architect

General Contractor: Griffiths Construction, Chester Springs, PA



Sympathetic Addition

Winner: Peter Zimmerman Architects

Adding History

By Martha McDonald

When a family purchased an 18th-century stone structure on a 36-acre property in the Okehocking Historical District of Willistown Township in Chester County, PA, they knew they needed to increase the size of the existing house to support their lifestyle. The program required sensitivity to the setting, appropriate traditional methods of construction and a sense of place on the property.

After interviewing several firms, the clients hired Peter Zimmerman Architects (PZA) of Berwyn, PA. The architects started with the core of the original house and expanded it with multiple additions totaling 7,310 sq.ft., bringing the new and renovated house to 10,654 sq.ft. “A large addition was carefully added to a relatively small structure, while maintaining a sensitive eye to scale, proportion, detailing and regional precedent,” says Peter H. Zimmerman, AIA, principal. “It was a challenging building site, sandwiched between a protected high-quality water shed with associated riparian buffers and nestled at the base of a very steep hillside festooned with scattered boulders and rock escarpments.”

Halfway through the design process, the clients moved into the house. “Having the opportunity to live on the property during the design process helped them crystallize their ideas to be consistent with the Pennsylvania stone farmhouse archetype of the 18th and 19th centuries prevalent locally,” Zimmerman adds. “In the process of developing the design, we arranged tours for the clients of a number of historic houses in the area to help illustrate how houses grew and were altered over the centuries as families’ needs changed.”

Since the property was located in a newly registered historic district, the architects had to get approval from the township’s Historical Architectural Review Board (HARB) for any work done on the property. “Every modification, demolition or addition to the structures on the site required the approval of the board. As part of this process, the architects documented all of the original buildings present at the property,” says William H. Johnson III, AIA, project architect. “This then served as the reference point for identifying and seeking permission from the board to selectively remove inappropriate additions and execute directed demolition to reveal the original architectural fabric of the stone structure.” After peeling away a previous slab-on-grade frame kitchen wing, a dark leaky room built over a terrace and various porches and partitions within the house, the new additions were attached to the core structure, one on the back, northwest corner and the other on the opposite corner at the front of the house.

The smaller, less formal addition (1,250 sq.ft.) in the back includes a guest suite, billiards room and screen porch, and the larger and more formal addition (5,856 sq.ft.) now represents a major portion of the house – the living room, a stair hall, kitchen, family dining room, butler pantry, glazed porch, family entry, mud room and powder room. The original house – now embedded within the new composition – became the formal dining area, the family living room and the library.

Cues were taken from the linear footprint of the existing house, which stretches along the toe of the south-facing slope. From this spine, the new masses were extended into the landscape, creating new outdoor rooms engaging the landscape while satisfying the needs of the interior program. This served to reduce the perceived scale of the new whole while embedding the existing volumes “seamlessly” within the new massing. Where the buildable area at the base of the hill opened toward the existing bank barn, the axis of the largest and most formally conceived section and entry was turned, creating an entry court bounded by the house and outbuildings and the forested hillside above the parking area.

Creating a cohesive whole was one of the primary design objectives. “The proportions of the main mass and the general growth of this house as it extended along the side of the hill helped establish a hierarchy of volumes and a plausible visual history,” Zimmerman notes. “The progression starts with the more formal three-bay mass at the front entry and steps down in scale, formality and detailing, terminating at porches or framed vistas into the landscape.”

Each of the new additions to the original house was treated and detailed individually to reinforce the growth process of the house. They were each conceived as occurring within a specific historic timeframe and were accurately detailed to that era with differing, yet historically appropriate moldings, millwork, glazing and stone detailing. The concept was that the original family, more prosperous in later generations, would have been able to hire skilled craftspeople from the growing pool of journeymen in the region. Like the woodwork and other details, the more formal stonework applied to the formal entry was designed to reinforce the difference between volumes. This shift in formality was further expressed at the three-bay mass through the tightly jointed “V”-pointed stonework, the more elaborate exterior millwork and the arched fanlight set within the pedimented front door millwork surround. The stonework coordinates with the stone on the rest of the house, though deviates with a finer quality.

The architects, with the assistance of Griffiths Construction of Chester Springs, PA, were diligent in finding and incorporating an extensive amount of antique materials in the renovation and additions. Worn antique marble from houses in the region was used for exterior doorsills and stoops and boulders from nearby Ridley Creek were used for other less-prominent doorsills. Salvaged seeded period glass from three separate eras was used to construct the new windows and doors and antique King of Prussia marble surrounds and antique brick hearths were installed according to the unique scale and proportion of each room.

The building stone for the exteriors of the additions was carefully blended to harmonize with the stone exposed at the house, barn and at structures on neighboring properties. Subtle variations in the way the stone mason went about “laying-up” – setting corners, pointing and composing the mortar – resemble the existing but suggest the variance of time and the touch of different hands in the construction. Remnants of the original millwork, along with other regional historical examples, formed the basis for all of the architectural millwork in the house. Original window openings and entry-door locations were allowed to remain unaltered for the most part, though all were upgraded or rebuilt. All of the original doors and hardware were salvaged from the original house, restored and reused. Almost all of the brick pavers were salvaged from the terrace on-site; these were supplemented by similar antique paving and building brick sourced from local suppliers where quantities were limited. These varying antique bricks were used at the chimneys, fireplaces, interior exterior floors and at selected porches and walks.

The clients embraced the idea of living in a house with a strong historical precedent. Within this context, each of the rooms was designed specifically to support their needs. All of the architectural and running millwork reinforces the historic storyline of the house, including fireplace mantels, cabinetry, paneled-door jambs, board and paneled wainscoting, custom stairs, balustrades and library casework.

The floors were fabricated from a variety of materials and treatments, ranging from reinstalled antique floors to planks resawn from antique beams. Antique bricks were used in small areas in a variety of patterns and antique and historically accurate doors and hardware were used throughout the house. Most of the hardware was taken from the original house and was restored or replicated by Michael M. Coldren Co. of North East, MD, and reinstalled. The firm supplemented the hardware with antique hardware that Coldren had collected and also produced many of the light fixtures.

The additions and renovations were built using entirely traditional materials or are, in fact, “green” construction. Products containing glues, formaldehyde or other high VOC finishes that might emit gas naturally over time or during a fire were not used. This excluded plywood, engineered joists, beams and other modern construction materials, necessitating the use of solid-board sheathing. Most of the finishes were achieved with milk paints, lime washes and glazes.

In addition to designing the main house, the architects also renovated an existing barn and replaced a frame garage with a period, regional style, run-in shed, which was inspired by a similar structure at the nearby Friend’s Meeting House. A stone retaining wall with a short picket fence does double duty, coordinating the transition between the barn and farmyard across the new entry court to the main house as well as keeping deer out of the garden off of the kitchen. The stonework on the barn and at the farmyard enclosure was gently cleaned with walnut shells to remove the accumulated layers of paint, white wash and plaster from the stone without disturbing the original patina before re-pointing.

The proximity and placement of these outbuildings in the landscape helped solve an aesthetic issue and improve the efficiency and performance of the HVAC system. There was a concern with the proliferation and sound of condensing units immediately around the house. The solution was a remotely located chiller, using the existing barn and banked entrance to screen the condensers from view towards the house and lane. Chilled water from the barn is piped to a holding tank in the basement and directed via manifold to the air handlers. The total tonnage of the system was reduced by the efficiency of this arrangement, decreasing the energy required to cool the house by cycling as many or as few condensers as required to handle the collected load. It also minimized the number and size of the condensing equipment that had to be hidden from view.

The family moved out when demolition began and, after 2½ years of construction, moved into their new-old home at the end of 2004. Both the clients and the architects embrace the notion of being curators or stewards of this property for generations to come.  



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