LESSONS LEARNED FROM RESTORATION OF ARCHITECTURAL TERRA COTTA ROOFING NICHOLAS FLOYD, PE; AND SUSAN L. KNACKBROWN, PE SIMPSON GUMPERTZ & HEGER, INC. 41 Seyon St., Waltham, MA 02452 Phone: 781-907-9000 • Fax: 781-907-9009 • E-mail: ntfloyd@sgh.com 2 7 T H RC I I N T E R N A T I O N A L C O N V E N T I O N A N D T R A D E S H OW • MA R C H 1 5 2 0 , 2 0 1 2 F L O Y D • 2 1 ABSTRACT Many historic buildings used mortar-set architectural terra cotta as decorative roof elements, relying on the terra cotta system as “waterproofing.” Such systems frequently leak or deteriorate over time due to ongoing water absorption, requiring extensive repair or complete replacement in order to meet contemporary water infiltration and structural performance standards. Design of new/replacement terra cotta elements must be soundly attached to the structure, while also incorporating a secondary flashing system below. Thermal movement and future maintenance must also be considered. Through multiple case studies, this presentation will outline the steps necessary to evaluate existing systems, design replacement systems, and successfully install architectural terra cotta roofing. SPEAKER NICHOLAS FLOYD, PE — SIMPSON GUMPERTZ & HEGER, INC. WALTHAM, MA NICHOLAS FLOYD, PE, is a Senior Staff II at national engineering firm Simpson Gumpertz & Heger Inc. He specializes in the investigation and remedial design of building enclosures, particularly historic buildings, plazas, and large public structures. Mr. Floyd has experience investigating and designing repairs for slate, copper, and various membrane roofing systems, brick and stone masonry, plaza waterproofing, and architectural terra cotta. Mr. Floyd has an architectural engineering degree from the University of Texas and is industrial rope-access trained. 2 2 • F L O Y D 2 7 T H RC I I N T E R N A T I O N A L C O N V E N T I O N A N D T R A D E S H OW • MA R C H 1 5 2 0 , 2 0 1 2 LESSONS LEARNED FROM RESTORATION OF ARCHITECTURAL TERRA COTTA ROOFING INTRODUCTION In the late 19th and early 20th century, architectural terra cotta was frequently used for decorative roof elements (Photo 1). The terra cotta tiles were typically mortar-set or used mechanical attachments with limited flashing (Photo 2). As a result, these installations frequently leak and are prone to deterioration of terra cotta and mortar, as well as attachment hardware corrosion, particularly as they are often installed at exposed roof areas such as ridges, hips, and finials. The systemic problems with these original roof installations typically cannot be fixed with topical repairs. Often, the most effective repair requires replacing the existing system with a new terra cotta “rainscreen” system that incorporates waterproofing and stainless steel attachments for hardware above the flashing. This paper discusses typical problems observed with historic architectural terra cotta roof installations, including both material and detailing defects and options being replaced with contemporary installa- Photo 3 – Clay can be hand-packed into molds (top) or ram-pressed (right). tions. To help in designing replacement terra cotta roof systems, this paper will provide guidelines both for replacement materials and detailing. WHAT IS TERRA COTTA? Architectural terra cotta is a fired clay-based material that is typically either hydraulically pressed, extruded, or hand-packed into its shape (Photos 3 and 4). The molds or dies used to shape the terra cotta pieces are typically based on models that are scaled up to account for 8% to 12% shrinkage that occurs during the manufacturing process. Achieving predictable shrinkage rates requires manufacturers to Photo 1 – Decorative terra cotta hip and ridge elements. Photo 2 – Terra cotta mortar set over lead flashing sheets and slate roofing; note voids in roofing and lack of additional attachment for these removed tiles. Photo 4 – Some terra cotta profiles allow for extrusion; note voids that are typical in the fabrication of all terra cotta units. 2 7 T H RC I I N T E R N A T I O N A L C O N V E N T I O N A N D T R A D E S H OW • MA R C H 1 5 2 0 , 2 0 1 2 F L O Y D • 2 3 have tight control on the manufacturing process, from initial mixing to final firing. Terra cotta tiles are typically constructed with 1- to 2-in. face shell and webs to reduce the weight of the tile and allow for drying during the manufacturing process (Photo 4). The mixture used for the architectural terra cotta body (or bisque) consists of a mixture of clay, water, grog (ground-up, previously fired terra cotta), various additives to control shrinkage, and soluble salts in the clay. Each manufacturer varies the proportions based on the desired body color, method of fabrication, and other variables. The tighter the control on proportioning and clay sources, the more consistent and predictable are the material properties of the terra cotta and finished piece dimensions. Terra cotta is typically finished with a glaze, which can either be a slip glaze (mixture of clay, water, and minerals) or a ceramic glaze (mixture of silica, water, and minerals). Once terra cotta is molded through one of the processes mentioned above, it is allowed to dry, often in a temperature- and humidity-controlled environment to prevent uneven drying and the resulting differential shrinkage and cracking. Once the unbound water has been removed, the pieces are ready for glazing and firing. Typically, the pieces are fired to a maximum temperature of approximately 2,500°F. As with all stages of terra cotta manufacture, controlled and consistent temperatures in the kiln result in tiles with more consistent material properties. Finished terra cotta is characterized by relatively low absorption, high compressive strength, and an expected life span of greater than 100 years, if properly detailed. The manufacture of terra cotta is a labor-intensive process from the initial fabrication of models to loading and unloading the kilns. The final quality of the product, therefore, heavily relies on the skill and care of individual workers. The process is timeconsuming; designers and contractors need to budget sufficient time (often months) to progress from shop drawings to shipping of finished tiles. HISTORIC TERRA COTTA ROOFING AND COMMON PROBLEMS Historic installation methods for terra cotta roof elements typically follow several models: The tiles were either set in place with mortar or concrete setting beds, similar to wall construction; were hung in place over bar stock, similar to slate roof details of the time; or were set in a combination of the two methods. With either method, there is often limited flashing installed below the tiles, and so the installation largely depends upon the surface seal of the terra cotta or shedding of water over lapping elements. Terra cotta, while having a low absorption rate itself (especially for tiles with ceramic glazes), is vulnerable at the joints between tiles. Typical joint details include either mortar or sealant installed in the joints or lap joints between tiles and roof components to limit water infiltration. Neither mortar nor sealant joints are waterproof in the long term, as mortar joints will absorb water, especially when installed at an angle where they have more weather exposure; and sealants fail over time. Compounding these problems is the fact that terra cotta roofing is often located in areas that are not readily accessible, making maintenance of mortar or sealant joints a difficult undertaking. Lap joints are only effective in steep-slope applications and are subject to water infiltration in high winds and with snow and ice buildup. Once water enters through terra cotta joints, it can degrade the mortar or concrete setting materials, corrode attachment steel, or cause interior leakage. As a result of water leakage, the structural attachment of the tiles can deteriorate, and surrounding construction is compromised, potentially damaging interior finishes or other roof construction. Frequently, tiles are damaged when the attachment steel corrodes or mortar- and concrete-setting materials become water soaked and undergo freeze/thaw damage. This damage exacerbates water entry into the system and causes further deterioration. It also makes it frequently impractical to salvage the terra cotta materials. Further, masonry or concrete was often installed between the webs of the tiles to provide a solid unit for setting or to embed anchors. Such masonry or concrete infill often prevents removal of the tiles without causing damage, and therefore further limits the potential reuse of the terra cotta materials. Some installations are built with a secondary roof or flashing below the terra cotta, such as a built-up roof, that does not match the lifespan of the terra cotta. If the durability of these materials does not match the lifespan of the terra cotta above, it can limit the effective life of the system. With the typical mortar- or concrete-setting details, it is typically not possible, when repairing or replacing an underlying roof when it begins to degrade, to remove and salvage the terra cotta. Complicating the systemic issues with the setting details outlined above is that the material properties of early terra cotta varied significantly. During the height of production (1880s to 1930s), limited standards existed to guide the manufacturing process. Quality control measures on proportioning, temperature, and humidity control did not exist. As a result, research has shown some of the terra cotta produced had high absorption rates and lower strength, making it more susceptible to damage, especially from freeze/thaw deterioration. The issues outlined above make it difficult for owners to repair and maintain their systems. Historically, repairs consisted of sealant or mortar repairs to the joints, secondary attachment to secure tiles, or repairs to individual damaged tiles. The durability of these types of repairs is limited to five to ten years and, given the difficulty and expense of access, was not usually implemented with the frequency necessary to limit damage due to water infiltration through the system. INVESTIGATING TERRA COTTA ROOF ELEMENTS The first step to designing durable repairs or a replacement terra cotta system is to understand the underlying causes for the deterioration and the existing construction detailing. This requires a hands-on investigation, which, given that terra cotta roof elements are often high up or on sloped roofs and difficult to access, can be expensive. Often a cost-effective and quick option is to use industrial-rope access (Photo 5). Hands-on access often reveals probable paths for water infiltration (Photo 6) that may not have been visible from below. Water testing allows the designer to confirm whether visible defects are leakage paths into the building or if a waterproofing below is providing secondary protection. Probe openings in the existing terra cotta system, whether from the interior or the exterior, are also an invaluable tool in developing repairs (Photo 7). Rarely do accurate or detailed original construction drawings exist; terra cotta tiles were often designed and built through the shop drawing process; and even if these shop draw- 2 4 • F L O Y D 2 7 T H RC I I N T E R N A T I O N A L C O N V E N T I O N A N D T R A D E S H OW • MA R C H 1 5 2 0 , 2 0 1 2 Photo 5 – Industrial-rope access used to review terra cotta hips. ings are available, they rarely show attachment or details for the underlying structure or flashing. Making probe openings allows the designer to do the following: • Determine all components of the existing system, including system geometry. The existing geometry is typically a critical factor when developing a replacement design, as the replacement tiles need to match the original terra cotta appearance. • Confirm the existing structural system used for the existing terra cotta tiles’ attachment. • Review the condition of buried structural components and confirm the existence of any secondary waterproofing system. • Sample materials to determine material properties and remaining lifespan, and also test for hazardous materials that may be present in sealants, mastics, or mortarsetting beds. A hands-on visual inspection and any subsequent testing or openings help the designers determine if the problems observed are systemic or the result of an isolated issue, allowing them to develop a competent recommendation for repairs. Probe openings and water testing also allow the owner to fully understand the extent of their existing problem and to understand the advantages and disadvantages of limited topical repairs versus a replacement terra cotta system. Knowing this information is critical, because if an owner chooses replacement, it is a costly and a relatively long construction process. GENERAL REPLACEMENT SYSTEM DESIGN CONSIDERATIONS Repairing systemic problems often requires complete removal and replacement of the terra cotta. In order to provide an effective replacement terra cotta roofing installation, the new system needs to meet contemporary design standards for water protection and structural performance. As such, contemporary repairs need to provide a roofing or flashing system below the terra cotta and cannot rely solely on its being waterproof. Terra cotta attachments must be integrated with both the existing structural system and this flashing or roofing system below. Successfully designing and installing terra cotta roofing requires careful detailing, as well as extensive coordination with the contractor and manufacturer through material testing and mock-ups. Photo 6 – Open cracks through terra cotta tiles that would not be easily visible from below. Photo 7 – Probe opening in terra cotta ridge aprons. 2 7 T H RC I I N T E R N A T I O N A L C O N V E N T I O N A N D T R A D E S H OW • MA R C H 1 5 2 0 , 2 0 1 2 F L O Y D • 2 5 In developing the terra cotta system and details, designers should consider some basic rules: • Any flashing and roofing materials below the terra cotta should have a lifespan that correlates to that of the terra cotta, or the design needs to provide for a way to remove and reinstall the terra cotta tiles to allow for replacement of the roofing system below. • All attachment materials above the roofing or flashing level should be stainless steel or other noncorrosive materials, as they will be in a damp environment. • In devising a waterproofing and attachment system, designers must also understand and consider the constraints of terra cotta material. Terra cotta is a custom-made masonry product; and even with highquality fabricators, there is often some dimensional variability from unit to unit due to shrinkage or warping during the firing process. Therefore, the terra cotta’s attachment design needs to provide for flexibility in the installation if tiles are to properly align and limit accumulated dimensional errors. • Designs need to provide for thermal and moisture expansion and contraction of the terra cotta materials, including the long-term moisture growth of the terra cotta tiles, which, like all fired-clay-masonry products, undergo long-term expansion due to the absorption of ambient moisture. As the thermal and moisture expansion rates vary from the metal flashing or framing members that are Photo 8 – Off-site malleable mock-up using plaster models. 2 6 • F L O Y D 2 7 T H RC I I N T E R N A T I O N A L C O N V E N T I O N part of the overall assembly, it is important to provide control joints or allow movement between tiles to prevent damage from differential movement between these materials. Even with a carefully thought-out design, mock-ups are a key component to the terra cotta installation process, and designers are wise to include these provisions in the project specifications. Mockups allow the designer, fabricator, and installer to understand limitations of the designed system and provide an opportunity to make improvements prior to full fabrication. Due to the long lead time and inherent difficulties in working with or modifying a fired terra cotta tile, the designer may wish to specify construction of an initial mock-up using a malleable material (such as wood or plaster) to replicate the terra cotta tiles. Using a malleable material allows the tiles to be shaved and easily modified to achieve the desired fit-up; these slight adjustments will help accommodate variations in the substrate and other system components that may not otherwise be apparent in the design and shop drawing process. Depending on the construction sequence, this initial mock-up can be constructed o-nsite or off-site on an armature replicating the existing conditions (Photo 8). Once complete, final terra cotta molds can be developed from these malleable mock-up tiles. A final in-situ mock-up with the actual fired tiles is also a useful tool to confirm installation procedures and any final fit-up issues before proceeding with the full installation. Beyond detailing, designers need to consider the material properties necessary for a durable and aesthetically acceptable installation. Unfortunately, ASTM has not yet developed standards specifically related to architectural terra cotta. Frequently, designers will refer to the requirements in ASTM C126, Standard Specification for CeramicGlazed StructuralClayFacing Tile, Facing Brick, and Solid Masonry Units. However, this specification, while providing general strength and appearance characteristics, specifically states that the requirements in the standard do not cover the minimum criteria necessary for durability of tiles exposed to exterior environments. Based on past projects and internal testing on terra cotta material durability, we typically included the following performance requirements in our specifications. A N D T R A D E S H OW • MA R C H 1 5 2 0 , 2 0 1 2 Case 1: Terra Cotta Hip Roll and Apron Using Hung Tiles Photo 9 – Terra cotta barrel roll and aprons set over lead flashing sheet and wire-hung slate roofing. Photo 10 – Extensive sealant over terra cotta joints, cracks/defects, and remedial face-fastened anchors. Note that criteria need to be adjusted for specific projects, and the designer should tailor to their specific project needs. • 8,000-psi compressive strength (tested per ASTM C39). • Maximum absorption of 6% (during 24-hr cold-water absorption test in ASTM C67). • Maximum saturation coefficient of 0.69 (when tested in accordance with ASTM C67). • One-eighth in. (±) dimensional tolerance for all length, width, and thickness dimensions; 1/16-in. (±) tolerance on all attachment holes. This also includes a stipulation to prevent accumulated growth of tiles. • Glazes can also be evaluated according to the testing criteria in ASTM C126, which includes a limitation that no defects or imperfections should be visible at a distance of 5 ft. Not all of the testing procedures in ASTM C126 are applicable for slip glazes, and the designer should review depending upon the project glaze requirements. Verification of the material properties specified should be done by completing material testing on the proposed project terra cotta. This testing should include initial testing prior to fabrication and testing during production. TERRA COTTA REPLACEMENT – CASE STUDIES The appropriate installation and attachment method will vary with each circumstance. The following case studies are intended as examples to discuss these design considerations and lessons learned. This case study building has four monumental hipped roofs covered with slate in the field and decorative terra cotta barrels and aprons along each hip (Photo 1). The original slate was tied to bar stock that extended between the rafters and main framing members. At the hips, the terra cotta tiles were mortar-set onto the slate and bar stock framing over lead flashing sheets (Photo 9). The terra cotta was original, dating to the late 1800s, though each roof was constructed in a different phase originally, and the tile geometry and material properties varied throughout. At some time during the subsequent 100 years, the tiles were resecured in place using face-fastened through-anchors and covered with sealant (Photo 10). The adjacent wire-hung slate in the field of the roof had been removed up to the edge of the terra cotta and replaced with new slate, plywood decking, and underlayment in the 1960s. These repairs eliminated leakage problems in the field of the roof, but the building still experienced chronic leakage through the terra cotta perimeter elements. As a first step, we performed a hands-on inspection of all terra cotta areas using industrial-rope access and water-tested the roof and terra cotta components to confirm leakage paths through the system. We also performed isolated removals or inspection openings to understand the hip tile’s existing geometry and attachment and to provide material samples that could be tested for compression strength and absorption testing in our laboratory. At the beginning of our investigation, we considered salvaging and reusing existing tiles in order to maintain the building’s historic fabric; however, once we reviewed and cataloged the condition of each terra cotta tile, we observed that a high percentage of tiles required extensive repair or replacement in order to be reused. We also found that some of the terra cotta on the project had high absorptions and low compressive strengths, suggesting that the material would not continue to be durable in the foreseeable future. After review of this information, the owner elected for full replacement of the terra cotta. 2 7 T H RC I I N T E R N A T I O N A L C O N V E N T I O N A N D T R A D E S H OW • MA R C H 1 5 2 0 , 2 0 1 2 F L O Y D • 2 7 In our replacement design, we elected to hang the new terra cotta tiles with stainless steel struts and attachment clips, which allow for a drainable, watertight copper flashing and continuous membrane underlayment below (Photo 11). The copper flashing was integrated with step flashing for the adjacent slate. In order to attach these struts and provide a continuous substrate for the copper and membrane, we also ilar bolted hung attachments to confirm our strength and modulus-of-rupture assumptions (Photo 12). The existing hip terra cotta has since been removed and replaced through four separate construction phases, utilizing three separate contractors. Each roof is slightly different in pitch and construction, hence the malleable and fired mock-ups included in our specifications remained a Photo 11 – Hung terra cotta hip detail and installed tiles. Photo 12 – Pull testing on proposed bolted apron attachment detail. designed a new steel hip plate and clips to attach this plate to the existing structural framing at the hip. The existing roof planes and hip framing on the building are not straight, so our design provided dimensional tolerance in the attachment system by use of the struts (allowing adjustability along roof slope) and shims between the new hip plate and the attachment clips (allowing up/down adjustability). The individual tiles can also be shimmed off the strut to accommodate variations in the terra cotta tiles themselves. Prior to the construction process, we constructed an initial full-scale mock-up in our office to confirm that this proposed design was constructible. We also performed testing on terra cotta tiles with simuseful tool through each phase and allowed for small modifications specific to each roof. Through the use of these mock-ups and in working with each installation contractor, we also made modifications to the design that eased the installation and improved the attachment or waterproofing system. These lessons learned include • In early phases, the barrel tile had a “bird’s-mouth” cutout to fit over the flared roll of the apron tiles, approximately replicating the configuration of the original mortar-set tiles on one of the roofs. This configuration proved difficult to install, as it limited the adjustability between the barrel and apron along the roof slope (Photo 13). In subsequent phases, the “bird’s mouth” was eliminated and the apron roll was instead trimmed to accommodate the barrel, allowing for greater adjustability but providing no real change in the finished installation’s appearance (Photo 14). This geometry detail matched one of the original tile configurations. • Original design included a short section of strut for each piece. The design was modified to utilize standard 10-ft. lengths of strut, reducing the number of flashing joints and attachment clips (Photo 14). • Hip plate attachments were modified to a thinner profile to better fit within the roof planes and limit interfer- 2 8 • F L O Y D 2 7 T H RC I I N T E R N A T I O N A L C O N V E N T I O N A N D T R A D E S H OW • MA R C H 1 5 2 0 , 2 0 1 2 Case 2: Terra Cotta Ridge Using Mortar-Set Tiles ’ ” ence with the step flashing while still providing adequate provision for beam clamp attachments to existing structural framing. The first phase of installation of these hips has been in service for approximately 10 years without any leakage, terra cotta failure, or problems with the attachment hardware. The same building as Case 1 also included a decorative braided railing at the roof ridges with decorative apron tiles extending onto the slate roof below (Photo 1). The ridge rail was originally set over lead flashing sheets; a reinforcing bar ran through the top of the ridge rail with limited rods tying the rail to the ridge steel below. The apron tiles were mortar-set directly onto the original wire-hung slate roofing. Similar to the hips in Case 1, the entire installation was covered with sealant from previous repair attempts, and some tiles were secured in place with remedial through-anchors. Also similar to the hips, the existing tiles had enough observed damage that the owner elected to replace these tiles. The rail is essentially several courses of stacked masonry construction, and the ridge provides a flat substrate on which to bear; we designed this portion of the assembly as a free-standing, reinforcedmasonry wall (Photo 15). In order to avoid the common problems associated with mortar-set terra cotta roofing, this design included the following: • Continuous copper flashing and membrane underlayment were placed below Photo 13 – Hip barrels with “bird s mouth to fit over apron roll. Photo 14 – Short sections of strut were originally provided for each piece (left); this was changed on subsequent phases to use 10-ft. strut sections (below), reducing the number of attachments and flashing transitions required. Photo 15 – Ridge detail and installed tiles; note interlock between tile courses. 2 7 T H RC I I N T E R N A T I O N A L C O N V E N T I O N A N D T R A D E S H OW • MA R C H 1 5 2 0 , 2 0 1 2 F L O Y D • 2 9 Case 3: Terra Cotta Tower Using Both Hung and Mortar-Set Tiles both the cap tiles (to limit water infiltration into the masonry system below) and the base of the rail (to prevent leakage into the building). Adequate weeps were provided to allow water that bypasses mortar joints to exit the system at these flashing locations. • Stainless steel threaded rods were used to reinforce the rail and to provide positive attachment to the structure below. A vertical rod was provided at 5 ft. on center with a continuous horizontal rod in the top of the rail. Continuous blocking was also provided at the top of the rail below the cap piece; this blocking was fastened to the vertical rods to put the assembly into compression as necessary to resist the bending moment from wind loads. Tiles with reinforcing rods were grouted solid to provide composite action between the masonry and reinforcing steel; all grouted tiles were vibrated to consolidate the grout and eliminate voids to help with freeze/thaw durability and to limit efflorescence. • The terra cotta tiles were designed to interlock between tiles such that the individual tiles were keyed into each other for a composite system. • Expansion joints in both the copper flashing and terra cotta rail allow for differential thermal movement along the ridge and accommodate longterm moisture growth. This system also required new steel framing attached to the existing ridge steel to provide a continuous substrate for the flashing and an attachment point for the new stainless steel anchorage system. This new steel framing also provided the opportunity to level inconsistencies with the existing ridge plane. The apron tiles below were hung using a stainless steel strut-and-attachment system similar to that used on the hips. As these tiles simply lay on the existing roof plane, they needed to be laid out and adjusted to accommodate variations in the tiles themselves and buildups in the layers of flashing material below. The final case study is a large decorative terra-cotta-clad tower on a transition masonry building constructed in 1919 (Photo 16). In the original installation, the lower portion of the octagonal tower’s double- angle steel framing was wrapped in metal lath and each course of mortar-set terra cotta tiles was secured with 4 to 8 in. of cast-in-place concrete backup poured into the space between the terra cotta and lath (Photo 17). At the upper portion of the tower, the terra cotta was similarly mortarset and then filled with cast-in-place concrete around a cruciform steel mast connected to the roof framing below. Upon construction, we observed a limited number of shelf angles embedded in the concrete and terra cotta to provide vertical support. The original installation has lead cams at some exterior joints, but no backup waterproofing to prevent leakage to the interior. We conducted a full hands-on inspection of the tower from both the interior and exterior and performed water testing using rope access. Several tiles had cracks or open mortar joints, some of which were covered with sealant or other coatings from previous repair attempts (Photo 6); when water tested, these defects resulted in almost immediate leakage to the interior. We made limited openings from the interior to determine the system’s construction and component thicknesses and to observe Photo 17 – Terra cotta was installed with cast-inplace concrete backup over metal lath and framing. Photo 16 – Forty-foot-tall terra-cotta-clad tower. 3 0 • F L O Y D 2 7 T H RC I I N T E R N A T I O N A L C O N V E N T I O N A N D T R A D E S H OW • MA R C H 1 5 2 0 , 2 0 1 2 Photo 18 – Terra cotta tiles are hung off a stainless steel attachment system, with metal decking and a plywood/membrane underlayment, and shingled-copper waterproofing system below. the condition of the steel framing. The lath and embedded steel elements exhibited fairly severe corrosion; but the primary framing members, which were inboard of the concrete fill, had only surface corrosion and no significant section loss. Given the condition of the existing tiles, the complications with the tiles being cast into the concrete backup, and the lack of an existing decking surface, we elected to remove the entire masonry system down to the existing steel skeleton. The octagonal tower’s structural framing was adequate to remain, but the cruciform mast did not have necessary capacity for contemporary wind and seismic loads unless the masonry was built tight to the mast to form a composite structure. Given the potential vulnerabilities of embedding mild steel in masonry, we elected to remove and replace the mast. On the lower portion of the tower, we provided for new steel decking attached to the existing framing members and a continuous roof system over the decking. The roof system consists of flat-seam copper roofing over a membrane underlayment on a plywood deck. This decking and waterproofing fit within the thickness of the old concrete fill so that we could maintain the exterior dimensions (Photo 18). The terra cotta was then hung from this decking, maintaining the same appearance and roof plane as the original. This hung system utilized stainless steel shelf angles at each course, and tiles were then pinned to the angle at top and bottom to provide lateral attachment; a similar system was used at the hips, but with custom stainless-steel attachment plates to accommodate the larger hip tiles (Photo 19). These angles and attachment plates were attached to a strut system similar to the concept from Case Study 1, which allows up/down adjustability in the system. Because of the planar appearance on each octagonal face of the tower, additional in/out adjustability was required at the top and bottom of each course to ensure all tiles remained in the same plane. As such, we designed the tiles to have oversized holes at the base and to be shimmed off of the support angle (oversized holes then filled to prevent rocking/rattling of the final tile); the angle attachment for the subsequent course could then be shimmed in/out off the struts to provide adjustability at the top of the course. The joints between the hung terra cotta tiles were filled with backer rod and sealant; this sealant will help shed water and maintain the joint appearance, while allowing for movement between tiles. In this design, the terra cotta system acts solely as a rain screen and does not rely on the relatively short-term life of the sealant joints in order to remain watertight. At the upper section of the tower, the mast was removed and replaced with a new galvanized steel tube and base plate on which the upper portion of terra cotta was stacked. This plate and tube were covered Photo 19 – Stainless steel angles, pins, and attachment clips connected to stainless steel struts. 2 7 T H RC I I N T E R N A T I O N A L C O N V E N T I O N A N D T R A D E S H OW • MA R C H 1 5 2 0 , 2 0 1 2 F L O Y D • 3 1 with membrane and metal flashing, and the upper terra cotta tiles were simply mortarset on top of the base plate. The void between the terra cotta and mast remained open to allow water to reach the flashing below and exit the system. To provide lateral tieback, we designed stainless steel plates that fit over the mast at each course and stainless steel pins to insert into each mortar-set tile (Photos 20 and 21). Similar to Case Studies 1 and 2, we specified malleable and insitu mock-ups to work out installation issues and ensure proper fit-up over a variable existing structure. Through this process, we made adjustments to the designed system: • The installation contractor elected to field-drill all the holes in both the stainless steel angles and the terra cotta tiles. This took additional time and labor onsite, but provided for greater adjustability during fit-up. • We added sealant to each kerf and pinhole in the terra cotta. The connections do not rely on sealant, but rather the sealant acts as a holefiller to ensure a tight connection at these anchors and to prevent rattling or rocking of the piece once it is set in place. TERRA COTTA ROOFING LESSONS LEARNED Based on our experience investigating and restoring multiple terra cotta roof systems, we offer the following lessons learned: • Leakage and attachment problems with terra cotta roofing are often systemic and cannot be properly addressed with topical repairs. • While the terra cotta material itself is reasonably water-resistant, joints in the system are vulnerable to leakage. Terra cotta roofing, therefore, requires a continuous substrate and flashing below to prevent leakage. • Structural attachment of each tile must be considered, including lateral loads. Selected materials should be corrosion-resistant if above the plane of roofing or flashing. • Terra cotta—particularly hung tile— requires provisions for adjustment or shimming to ensure proper fit-up and to account for dimensional tolerances in the terra cotta and variations in the attachment or existing structural system. • When incorporating a flashing below terra cotta, the designer needs to provide for a drainage path so that water can exit the system. • The designer should consider potential efflorescence issues when installing mortar-set tiles. • The design must accommodate differential thermal and moisture expansion. • When properly specified and fabricated, terra cotta can last for centuries and may have a greater lifespan than some of the adjacent roofing or flashing materials. If possible, new designs should allow tiles to be removed and salvaged (i.e., not grouted solid or epoxied in place). • Specifications need to provide specific material requirements and dimensional requirements for the proposed system. • Mock-ups are an invaluable tool in the terra cotta design and installation process; a mock-up that is both malleable and insitu should be included in the specifications with clear direction on what components and areas to include. Photo 20 – Mortar-set tiles with stainless steel plate and pins for lateral attachment to mast. Photo 21 – Completed tower installation. 3 2 • F L O Y D 2 7 T H RC I I N T E R N A T I O N A L C O N V E N T I O N A N D T R A D E S H OW • MA R C H 1 5 2 0 , 2 0 1 2
