Track 2: Materials over Time: Points of Change

General Abstract

3 - Taking an Alternate Approach – Replacing Architectural Terra Cotta

Wednesday, September 26
8:30 AM - 10:00 AM
Location: HYATT-Grand EFG

Architectural terra cotta was developed as the durable and affordable 19th century alternative to carved stone, with initial uses that mimicked the appearance of natural stones. Early anchorage details were also inspired by similar stone anchorages and suffered similar limitations of deterioration due to water infiltration, corrosion, and unaccommodated differential movement. Terra cotta design and detailing evolved as the industry matured with better quality production, improved anchorage details, and designs and patterns that moved away from just mimicking stone. Modern rehabilitation projects that replace deteriorated terra cotta similarly need to evolve to consider both alternate materials and anchorages. Using The First Church of Christ Scientist Mother Church terra cotta replacement project as a case study, this presentation will examine how the design team evaluated alternatives for both materials and anchorages to find the most appropriate approach considering durability, historical appropriateness, constructability, schedule, and cost.

A significant extension was added to the Mother Church at the turn of the 20th century, which features carved granite and limestone facades with terra cotta domes, semi-domes, and smaller roofs. The current multi-year restoration project includes replacement of the two semi-domes, which have a history of ongoing leakage and deterioration that a previous replacement project, within 15 years of the original construction, did not address. Currently mortar set over a membrane waterproofing on a Gustavino thin-shell structure, the semi-dome terra cotta suffers from water infiltration, freeze/thaw deterioration, and cracking due to unaccommodated movement. As currently designed, there is also no easy way to repair or address hidden defects. It was the design teams charge to develop a system that is durable for 75 to 100 years, salvages the Gustavino structure below, provides reliable waterproofing, and can be maintained and worked within the Church’s budget. This presentation will discuss our analysis and options considered in arriving at our design.

Within the narrative of this project, the presentation will review:
• Causes of deterioration of the existing terra cotta roof system
• Evaluation of the Gustavino sub-structure and impacts of roof alternates on its function.
• Anchorage and waterproofing considerations to prolong durability and allow for maintenance, including the selected unique cable attachment system design
• Replacement material options, including machined stone and replacement in-kind. The analysis will present our material testing and evaluation to compare durability, constructability, and maintenance aspects of the material options.

Learning Objectives:

Casey Williams, PE

Senior Staff II
Simpson Gumpertz & Heger

Casey Williams, P.E., is a Senior Staff II at Simpson Gumpertz & Heger, Inc. (SGH) in the Building Technology group. She has been involved with the investigation and remedial design of building enclosures, as well as the subsequent construction administration of repairs, including the New York State Capitol, the Massachusetts State House, and the First Church of Christ Scientist. Her focus is on historic building investigation and repair projects. Ms. Williams has experience investigating and designing repairs for slate, copper, and various membrane roofing systems, brick and stone masonry, and architectural terra cotta.


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Chris Gembinski

Building Conservation Associates, Inc.


Chris is the Director of Technical Services for Building Conservation Associates, Inc., providing quality control and technical oversight for all BCA projects. Through his investigative work on hundreds of historic properties, he has developed extensive expertise in historic construction techniques and building systems, architectural materials, preservation design solutions, and construction management. Various aspects of his research and design have included masonry restoration, plaster restoration, historic finishes analysis, wood and metal window restoration design and stained-glass restoration. His work includes the design and management of conservation and preservation construction for: The Metropolitan Life Insurance Building, Grand Central Terminal, St. Patrick’s Cathedral, the Central Park Police Precinct, the Cathedral Church of St. John the Divine, and Trinity Chrch, Wall Street, as well as development ventures such as the Victoria Theater and Moynihan Station Redevelopments.


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3 - Taking an Alternate Approach – Replacing Architectural Terra Cotta

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