Convent of the Sacred Heart School (1 East 91st St)
Project Statistics
Project: Façade restoration of the Convent of the Sacred Heart School
Location: 1 & 7 East 91 Street, New York City
Client: Convent of the Sacred Hearts School
Project dates: 2023-2025
Services provided: Façade Restoration and Repairs
Building type: Steel Frame structures clad with limestone. Both buildings listed on National Register of Historic Places, New York State Historic Preservation Office, Individual New York City Landmarks
Overview
The Convent of the Sacred Heart School, located in the Upper East Side of Manhattan, is housed in two historic buildings: the former Otto Kahn Mansion (1 East 91st Street) and the former James A. Burden House (7 East 91st Street). These buildings, constructed in the early 20th century, are listed on the U.S. National Register of Historic Places, recognized as a New York State Historic Preservation site, and are designated as individual New York City Landmarks.
CANY was contracted to conduct a comprehensive restoration of the buildings’ exteriors, maintaining historical integrity and safeguarding the future of this important educational institution. The project addressed material deterioration, structural integrity, and aesthetic preservation in compliance with the New York City Landmarks Preservation Commission (LPC) regulations.
CANY's Involvement
Services provided
While both buildings operate as a single school, each mansion presented unique material and restoration challenges, requiring a tailored approach. CANY conducted a full building enclosure assessment and developed a restoration strategy, ensuring compliance with the LPC, and executed meticulous restoration efforts for each structure.
Scope of work
Comprehensive Conditions Assessment - A detailed investigation of the limestone facades, brick masonry, copper elements, Spanish clay tile roofing, and decorative plaster to identify deterioration and underlying issues.
Material Analysis & Testing– Destructive and Non-destructive Testing of historic limestone, brick, mortar, and plaster to determine appropriate restoration techniques.
Structural Reinforcement: Evaluation, testing and treatment of embedded steel components to prevent future deterioration.
Restoration & Monitoring: Oversight of repairs, regular site inspections, scope reviews, and oversight of material application, ensuring materials and methods were historically accurate and structurally sound.
Cleaning: Localized cleaning of limestone.
Compliance: Coordination with the New York City Landmarks Preservation Commission.
Our approach and solutions provided
Main challenges
Material Degradation: Severe crumbling of the St. Quentin limestone due to its high absorbency and low compressive strength, proving its incompatibility with the Northeast's freeze-thaw cycles and the use of incompatible repair materials used in past restorations.
Structural Concerns: Deteriorated steel components and added loads from modern infrastructure required careful testing of historic material and specific reinforcement details.
Material Sourcing Issues: Original St. Quentin limestone was unattainable, necessitating a suitable alternate replacement.
Landmark Compliance: Strict preservation regulations required meticulous documentation and approval for all restoration efforts.
CANY's solution
Custom Material Matching: Due to sourcing challenges, Vaio Galina Limestone from Italy was identified as a suitable substitute based on compression and absorption testing.
Advanced Testing & Analysis: Conducted destructive and non-destructive material testing, including Gravimetric Mortar Analysis, to determine appropriate mortar compositions for repairs, compression and absorption testing of the St. Quentin Limestone, and plaster analysis of the historic plaster within the carriageway of 1 East 91st Street. Cleaning tests were performed at the existing limestone balustrades of 1 East 91st Street to determine best methodology for localized limestone cleaning.
Structural Reinforcement Strategy: Coupon Testing was performed on historic steel to assess strength and welding compatibility. Preheating was recommended before welding due to high phosphorus content.
Precision Repair Specifications: Specification of proper preparation, curing, and application procedures on all limestone pointing, crack repairs, and patching including use of Natural Hydraulic Lime (NHL) mortar to complement the absorptive and compressive nature of St. Quentin limestone
Landmark-Approved Restoration: All material sample mock-ups were submitted for approval to ensure historical accuracy and compliance with preservation standards.
Project Achievements
Key outcomes
Improved Durability: Restoration efforts strengthened the building enclosures/envelopes, improving their resistance to climate and environmental stressors.
Historical Integrity: All materials and methods were carefully matched to the original construction to ensure historical authenticity.
Enhanced Safety: Structural reinforcements and compliance measures improved the safety of both the buildings and those who use them.
Landmark Compliance Success: The project met all regulatory requirements, ensuring the preservation of these historic landmarks for future generations**.**
Building History
The Convent of the Sacred Heart School, on the Upper East Side of New York City, is a private Catholic girls’ school, comprising the former Otto Kahn Mansion (1 East 91st Street) and neighboring James A. Burden House (7 East 91st Street).
Philanthropist Otto Kahn, who bought the plot from Andrew Carnegie, built the mansion as a family home. Designed by architects J Armstrong Stenhouse and C PH Gilbert in the neo-Italian Renaissance style, it was completed in 1918 and sold to the Convent of the Sacred Heart School after Kahn’s death in 1934. Carnegie was also the original owner of the plot for the James A. Burden House which was later sold to Burden’s father-in-law. He commissioned the house to be built as a wedding gift for his daughter, Florence Sloan. Designed by architects Warren and Wetmore in the Beaux Arts style, it was completed in 1905, and bought by the Convent of the Sacred Heart School in 1940, originally as boarding accommodation for the school next door.
These two beautiful mansions, connected via a modern glass walkway, are both listed on the United States National Register of Historic Places, recognized as New York State Historic Preservation sites, and are individual New York City Landmarks, under the auspices of the Landmark Preservation Commission (LPC).
Conclusion
CANY’s expertise in historic preservation and their meticulous approach to material analysis ensured that these beloved buildings were restored with the utmost care and precision. Maintaining the integrity of these valuable landmarks means they continue to provide a rich educational environment for future generations.
