Replacing the Ceiling at the Glass House

By Forum Online posted 06-01-2018 15:17


In 2015 staff at the Glass House—a National Trust for Historic Preservation historic site—observed a noticeable sag in the ceiling. It had dropped low enough to disturb the swing of two doors, and the dips were visible from outside the building. The investigation team discovered that the wood framing for the metal lath had been attached using nails, and over time, the weight of the plaster had pulled the nails down and out of the roof framing.

Finished Glass House Ceiling March 2018
Finished Glass House ceiling, March 2018 | Credit: Michael Biondo

Staff at the Glass House and National Trust assembled a group of consultants to tackle the ceiling repairs. EverGreene Architectural Arts served as the conservator and specialty contractor on the project, and the structural engineers were from Silman. American Environmental handled abatement, DUN-RITE Specialized Carriers ensured protection, and Michael Biondo assisted with photo documentation. 

The internal project management team included Greg Sages, executive director of the Glass House; Brendan Tobin, Glass House manager of buildings and grounds; and Ashley Wilson, AIA, Graham Gund Architect. 

Allison Semrad, Silman Fellow for Preservation Engineering at the National Trust—aided by members of the project management team—told us about the process of replacing the sinking ceiling.

Stabilization of the ceiling in 2015 (Photo courtesy of EverGreene Architectural Arts
Stabilization of the ceiling in 2015 | Credit: EverGreene Architectural Arts

What steps did the Glass House staff take initially upon discovering that the ceiling was sagging?

As an emergency repair, the staff arranged the installation of plaster washers and screws to stabilize the ceiling and prevent further displacement, allowing the site to stay open. Once that was done, EverGreene Architectural Arts began studying existing conditions and made a pressing discovery: the finish coat of plaster contained asbestos. Because of the structural deficiencies and the hazardous material, the team could no longer consider localized repairs—the entire ceiling had to be replaced.

Temporary construction door and protected cabinets | Credit: Michael Biondo

What was the next phase of the project?

A hazardous material abatement team removed the plaster, metal lath, and related furring strips, exposing the roof structure above. Once the old ceiling had been removed, the project team inspected the exposed roof framing structure, which turned out to be generally in good condition. Nonetheless, the team took advantage of the fully exposed structure to reinforce some roof joists under Siman’s guidance. Joists that were badly knotted or overstressed were sistered with laminated veneer lumber. Following structural repairs, new furring strips to attach the metal lath were installed to match the original configuration. This time, the components were screwed, rather than nailed, into place.

How did the team replicate the plaster for the new ceiling?

Painstakingly! The Glass House has a three-coat plaster system that includes a scratch coat, brown coat, and a finish coat. EverGreene studied salvaged plaster samples to determine replacement mixes. The first two coats were replaced in kind. The finish coat had to be formulated without asbestos, but still match the original ceiling’s stucco-like appearance and warm brown color. EverGreene tried six trial mixes before finding an appropriate replication. Toland Grinell, EverGreene’s project manager, discusses the process in this Curbed article by Jenny Xie.

Roof structure after the ceiling was removed | Credit: Michael Biondo

Did the team encounter any surprises in the course of replacing the ceiling?

During demolition, the team discovered metal pipes embedded in the plaster above the dining table, bedroom, and sitting areas of the house—remnants of a radiant heating system. 

Salvaged pieces of the ceiling with embedded piping (NTHP Photo)
Salvaged pieces of the old ceiling with embedded piping | Credit: National Trust for Historic Preservation

Philip Johnson included underfloor radiant heating systems in many of his residential projects, but little is known about his decision to include a ceiling system in the Glass House. In 2007 long-time site engineer Port Draper mentioned the heating in an interview with The New York Times

“There used to be radiant heat in both the ceiling and floor. But the ceiling heat died many years ago for some reason. I think it froze. He ran the floor so hot you couldn’t go in there with bare feet—you’d burn them. When it got really cold out there, the system would practically put 200-degree water in the floor.” 

Even though these plaster-embedded heating pipes seem obscure and experimental today, the system would not have been unique in the 1940s. Such systems were published in the American Society of Heating and Ventilating Engineers Guide (predecessor of the ASHRAE handbook) as early as the 1930s. The ceiling systems required cooler running temperatures than their underfloor counterparts, as plaster was more susceptible to cracking caused by temperature-induced movement of the metal pipes. 

Diagram from the 1939 Heating Ventilation Air Conditioning Guide | Credit: American Society of Heating and Ventilating Engineers through

The forgotten system at the Glass House was not immune to the problems associated with plaster-embedded radiant heat. Stains previously attributed to roof leaks may have actually been caused by leaking water pipes. Differential temperatures between the water in the pipes, the metal, and the plaster would likely have created condensation, causing even more stains on the ceiling. Draper’s suggestion that the system froze makes sense given the piping’s location just under the flat roof and its cooler running temperature. As the system was embedded in the plaster, repairs would have been difficult and costly. For these maintenance reasons, piped radiant heating is no longer common, and the new ceiling does not include this long-forgotten component.

Installing new ceiling framing after completing structural repairs | Credit: Michael Biondo

How long did it take to replace the ceiling?

Staff discovered the damage in 2015, and the team completed repairs in spring 2018. In those three years, the team raised the necessary funds; created the work plan, including collections care; and publicly bid the project. Construction started at the end of 2017, and the new plaster went up in March 2018. The collections were re-installed in April in anticipation of the Glass House’s reopening in May.

New ceiling framing and metal lath | Credit: Michael Biondo

How did you protect the collections during construction?

In early December 2017, DUN-RITE protected the sculptures, furniture, and the painting and moved them out of the building. Even the door was temporarily replaced to lessen wear and tear. The core of the building and the floors were protected in place, as were the large-scale cabinets. The cabinets were enclosed in cushioned plywood under a plastic frame.

Applying new plaster and samples | Credit: Michael Biondo

How much did the project cost, and how was it funded?

The project cost about $230,000. The Glass House secured funding from two sources: Bank of America’s 2016 Art Conservation Project and the state of Connecticut’s Department of Economic and Community Development Good to Great program grant.


Preservation projects require a careful balance of priorities between retaining historic fabric and making historic sites safe. Due to the original construction techniques at the Glass House and the hazardous materials used in the plaster, retaining the original material was not an option. Care was taken to create ceiling plaster that would resemble the texture, size, and color of the original as closely as possible while creating safer conditions.

Want more on the Glass House ceiling project? Check out this piece on

Time Lapse Videos

Collection Protection

Lath and Mesh Installation

Plaster Scratch Coat

Plaster Brown Coat


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