Dept. of Justice Terra Cotta Antefixae Retrofit & Repair
Washington, DC: 2000
Using the "drop" to repair, retrofit, and reinstall terra cotta ornamentation on the Department of Justice Building in DC allowed conservators to prove the value of saving historic material while saving the government more than $2,000,000.
Many of both the large and small terra cotta antefixae that ring the building perimeter, some weighing as much as 35 pounds, had broken free under heavy snow loads and were lying in the gutter. Believing that these broken pieces need to be replaced, GSA had budgeted for replacement at $4,000/each and estimated they needed at least 100 large units.
A conservation team was brought in to determine the cause of failure, design a better means of attachment to the roof deck that would overcome this design weakness, and oversee the making of replacement units. Yet with the attic nooks and crannies all packed with broken units of several generations, the team soon came to the conclusion that a better starting point would be to inventory what might be salvageable from the broken units.
An Alternate Approach is Proposed
Since hundreds of salvaged units more than filled all of the gaps on the roof and that most of these had damage only at the tail which was covered by the tiles above, the conservators suggested a new set of goals:
- 1. Design a retrofit armature that reduced the stress concentrated at the tails;
- 2. Develop a repair method for broken antefixae tails;
- 3. Develop a new terra cotta back for the most damaged units where only the polychrome faces could be salvaged, then devise a means of securing the new backs;
- 4. Carry out all repairs to secure new backs to original faces (25 units needed this repair);
- 5. Repair ten units (five large and five small) and reinstall these on the roof;
- 6. Document the repairs and reinstallation through written explanations, drawings, photographs and video to develop comprehensive specifications;
- 7. Provide contractor training in these one-off repair methods, and then supervise work.
The government initially resisted this approach because it included contractor training which is not normally funded. However, they eventually agreed, recognizing that the uniqueness of the repairs meant that no contractor could be expected to already have done work of this exact type, and thus they would need to be trained.
Triage and Development of the Repair Process
In order to design a repair approach, the first order of business was to build a roof edge mockup that would allow us to test the various retrofit options. (This roof mockup proved invaluable in educating the client and in proving the repair concept as well.) It was clear that most of the damage was due to an inherent weakness in the means of attachment. This design flaw was compounded when the roof was relaid fifteen years prior, adding yet more stress to the units on the roof.
The antefixae were originally attached with wire looped through two holes in the tail, where the terra cotta is thinnest. When the tiles were relaid on a new deck in the 80s, the installation added two additional stresses. First, by re-attaching the antefixae with wire through only one hole and using the wrong type of wire; and second, by randomly relaying the tiles so that the antefixae did not bear their weight evenly on the tiles below. Terra cotta inherently has irregularities and they cannot be relaid randomly as is possible with more uniform units of masonry.
The retrofit mechanism was developed in two parts with a web that was mortared into the body behind the decorative head of each tile and came to rest against the roof-mounted bracket. A small stainless J-clip was also added to grab the back of each terra cotta tail and hold it down to the roof, thus spreading the load and providing an additional level of reinforcement. Broken tails were to be rebuilt using jahn mortar over a reinforcement of stainless steel hardware cloth.
The Drop - A Repair Plan in Action
After designing the proposed repairs, it was time to execute a conservators' drop on 5 large and 5 small antefixae. Drops are a proof-of-concept where all of the stages of repair are carried out; first by the conservators and, in most cases, again later with contractor involvement. This repair process tests both materials and methods in the real world, allowing adjustments and uncovering hidden problems before the project goes out to bid.
Since bidding contractors received a video showing each step of the repair and installation being carried out, the specifications were not speculative.
The drop eliminates the surprises that often arise later in projects that had limited investigation. (Often referred to as "unforeseen conditions" that are inherent in working on historic buildings and covered under a 30% contingency fee, these knowable but often overlooked conditions regularly lead to historic building being cut to fit a pre-conceived design that never matched the real conditions on the building.) This process of sacrificing buildings because of an unwillingness to thoroughly investigate beforehand is unjustifiable.
Skipping the drop puts contractors in one of two unacceptable positions: either at risk of losing money for not having overbid to cover all "unknowns," or in the driver's seat to cut the building with abandon through change-orders once these "new" conditions are discovered. Using the drop to design the antefixae repair project led to the first change-order free project the senior GSA project manager had seen in his 20 years.
The significance of the Department of Justice project is not in the one-off repairs designed for the antefixae, but in the use of the drop. This process allowed the proposed methods and designs to be tested in real time, resulting in a proven repair plan that was fully fleshed out before the bid was issued. This meant the owner, contractor, and conservator could work together as a team. $4 million was the original budget just for replacement of antefixae. The drop approach proved broken units could be repaired and installed back on the roof with the new retrofit armature for half that estimate. The drop effectively saved both public money and important historic fabric. The project at DOJ shows that the implementation of a conservation drop as a pre-requisite to bid documents is a practical and economical model for preservation projects. And it's a process GSA has since begun to incorporate into other Federal Triangle projects.