| The November 1936 issue of LEAD, the journal of the Lead Industries Association, focused on “One of the finest buildings of its kind ... the monumental ... United States Court House.” This more than 40-story structure capped with a terra cotta mansard roof and crowned with a terra cotta lantern was declared a landmark building in 1984. Recently, it was rededicated as the Thurgood Marshall U.S. Courthouse.
Designed by Cass Gilbert, the courthouse was intended to withstand hundreds of years of use; hence, the choice of building materials. Among these was the flashing material which, although not visible to the eye, can ultimately result in a building’s success or failure in withstanding the elements over time. Cass Gilbert selected sheet lead for practically all of the waterproofing details. It was used as the waterproofing of foundations, the through wall and cap flashing, the main building gutter, the liner of the ledges, at the 28th floor in the lighting wells, for many of the roofing details, and even as the waterproofing for the shower stalls.
Recognizing the importance of designing a building to shed water, Cass Gilbert commented:
“Specific attention must be called to the users of sheet metal for flashing to the possibilities of expansion and contraction. No material is free from this movement, including brick, stone and concrete... In the Court House, the subject of expansion and contraction was given most careful study so each sheet of lead may have movement in itself. Loose locks made by folding the different sheets together were generally used to let each piece breathe.”
Nevertheless, Water Infiltration
For the past few years the General Services Administration (GSA), the building’s owner, has been involved with responding to water infiltration into the building. Repointing the masonry joints was determined to be the course of action to take. Masonry joints typically withstand 40 years of weathering, and as the courthouse has been standing for more than 75 years, the time had come for a comprehensive maintenance plan.
Investigation showed that although the joints had weathered and were clearly in need of repointing, this was not the cause of the water infiltration. Many of the horizontal rain water leaders rusted through and were leaking, and most of the lead flashing had failed over the years and was proving to be the most responsible for the leaking. It became particularly apparent that the “patented interlocking design” of the lead through wall flashing and the loose lock connections between through wall and exposed lead flashing allowed for the greatest water infiltration.
The article of 1936 specifically drew attention to:
“where lead flashing had to be caulked into reglets in the stone work, continuous lead locking strips were first caulked into the reglets and the lead flashing was loose-locked to these strips. Gutter linings were handled like cornice coverings with loose locked cross seams at 8-foot intervals. Where tile decks ended in parapet walls, interlocking cap flashing was installed to overlap base flashing with loose-locked cross seams. The base flashing was run under the tile deck. In some cases the flashing was entirely concealed. Where lead had to be fastened along cornice edges and similar locations, continuous cleats were fastened to the stone by means of lead plugs and brass screws inserted in holes drilled in the stone. The lead cornice covering or flashing was loose-locked to this cleat.”
It was thought that the three-pound and in some cases eight-pound lead (different weights, hence d ifferent thicknesses) that was used would have lasted forever. Yet it was this lead that apparently weathered, yielding to the water infiltration. Followed by steel oxidation and exfoliation, this weathering ultimately led to mortar and stone failure. Was this lead an alloy that reacted with the now documented acid rains of New York City, allowing for this decomposition over the years? Was it the movement of the lead itself due to expansion and contraction that caused the loose locks to loosen so much so as to cause gaps that allowed for water infiltration?
As more intense discussions developed regarding the maintenance of the courthouse, internal tours began highlighting the existing conditions and related damage to GSA staff and officials of the courts. A highpoint on the tour is the underside of the portico and main stairway leading to the entrance of the courthouse. It is clear that over the years water infiltration through the stairs caused structural damage. From the LEAD article we learn:
“In waterproofing the porticos, the entire floor was lined with sheet lead. At the base of the stone columns, which rested over the square raised pedestals, the lead waterproofing was turned several inches up the sides of these large dowel-like structures. A separate inverted lead pan was then made for each column and was placed over the raised base, overlapping the lead waterproofing turned up the sides by about 6 inches.”
A sketch from the article shows a section through the courthouse portico with lead sleeves around each portico step supporting beam. It is apparent that this lead flashing failed, allowing rain to infiltrate and ultimately corrode the steel reinforcement of the concrete structure upholding the stone stairs.
Investigations, studies, and maintenance are ongoing at the courthouse. The original article from LEAD offers good information and insight to guide professionals now, eighty years after the building’s completion, through their search and to the appropriate response to the maintenance of this grand municipal structure.
PB is Helping to Develop Diagnostic Testing
PB has been involved in a number of these ongoing maintenance projects and is under contract to GSA Region 2 Property Management Division to manage the repointing, gutter replacement, and rain water leader replacement, and to monitor the stair removal and rebuilding project. We brought in technical consultants from Wiss, Janney, Elstner Associates, Inc.(WJE) and Feld, Kaminetsky and Cohen Engineers (FKC) to join our team.
As a direct result of the repointing work, we observed the joints on the front parapet continually cracking in a number of locations due to stone movement. The removal of one stone revealed that the structural steel hangars had rusted away completely as a result of the extent of water that had infiltrated into the loose locked lead thru-wall flashing. The stones were resting on the base flashing below.
Cracking of joints continues to require our team to perform forensic studies to ascertain the source of these cracks. There may well be historic patterns of thermal stress or movement between individual granite facing stones or localized issues relating to leakage or rusting of encapsulated steel that can encourage joint cracking. At present, we are working with GSA to establish a testing program to “scientifically” diagnose the basis of the existing water infiltration issues. The PB, WJE, FKC team visually identified and mapped the cracks. The team then recommended petrographic testing of mortar be done and a long-term crack monitoring program be instituted to more precisely diagnose the causes of the cracks. If the program is instituted, the team will be able to prescribe a long-term maintenance program.
The State of Building Science
Max Abramovitz, the project architect for the United Nations building in New York City, presented to a conference on architecture education in 1949. He stated,
“... very few men are left today who are expert in building science. ... Those men are disappearing largely through the force of circumstances beyond our control,...
One would think we would know whether we can build a marble wall that will not crack and let water in. That sounds very simple. After all, they’ve been doing it for 3,000 years. Well, right now we’re having a hot argument about it on the United Nations building. We can’t find anyone who will say “I am sure it can be done this way,” or “I am sure it cannot be done.” We’ve asked old builders who have repaired the marble columns in St. Patrick’s Cathedral... I am sure many other architects are doing the same thing and that all of us are probably repeating each other’s mistakes. If one of us finds the answer, the rest won’t know about it. Yet, even if you’ve created a fine piece of architecture, it’s a terrific black mark against your reputation when a simple thing like a leak occurs.” (Proceedings of the University of Illinois Conference on Architectural Education, February 21-23, 1949. p. 134.)
More than a half a century has passed since Max Abramovitz made this observation and, yet, the void remains.
I propose we consider making a strategic decision to become experts of building science. Our experiences at the Thurgood Marshal U.S. Courthouse, General Motors and the United Nations buildings, to name only a few, provide lessons learned that should be documented and used as reference.
Each year more buildings are added to landmark registries. These precious buildings need building scientists to perform the forensics, diagnose the problems and monitor the corrective work. They need building scientists to create detailed maintenance manuals defining the myriad of maintenance tasks that need to be followed daily to keep a building in good order. They need building scientists who are familiar with what appropriate sustainable recommendations need to be made to take these buildings into and through the 21st century, able to meet modern energy codes and to successfully integrate state of the art technology, security and safety technologies.
PB is up to the task. Let’s take it! |
