Reliance on an exposed single barrier of sealant to prevent water penetration into an enclosure is the single most common source of contemporary building enclosure problems. Despite improved sealant technology and installation techniques, a single sealant barrier is only effective if it maintains its original seals. There are many problems that can lead to sealant failure – including weathering, poor workmanship during installation, incompatibil- ity, improper mix design, preparation of sub- strates, ultraviolet radiation. An enclosure design that relies on single seals for protection lacks the level of redundancy required for a leak-free building. A dual seal design provides
a continuous outer and inner seal at all transi- tion details. The outer seal can fail, and the system will still resist water and air infiltration. A dual seal system allows the primary seal (the one on the inboard side of the system) to be sheltered from rain, sun, and birds. All of the elements could adversely affect its per- formance. The outer seal can be seen as a sacrificial element.
Water Damage
Penetrating water can be a nuisance for build- ing occupants. A leaking window can chip paint. Infiltrating water at the base of a wall can stain carpeting. However, the worst water damage on a building can be hidden from view and trapped inside the wall system. Completed in 1986, the Imperial Polk County Courthouse in Bartow, Florida, is a ten-story concrete-frame structure clad with brick veneer and clay tile roofing. With a reasonable construction budget of 35 million dollars, the courthouse was expected to serve its commu- nity for many years but it did not. Instead, it proved to be an infamous example of how much damage infiltrating water can do to a building. The courthouse was plagued with serious water infiltration shortly after comple- tion. Leaks from the clay tile roofing system and brick veneer flashing intersections led to water damage on the interior. At the same time, the brick veneer on the tower had devel- oped severe cracks and bulges. Pieces of masonry literally fell off of the building. Com- plicated by problems with the HVAC system and the use of a vinyl wall covering at the perimeter of the building, the courthouse showed chronic symptoms of “sick building syndrome” and was vacated in 1991, just five years after opening.
Although the building is an extreme example of construction-related problems, the water infiltration through the brick veneer is a classic example of a failure that occurs on many buildings. The exterior wall consisted of brick veneer, cavity space, reinforced concreted masonry units (CMU), insulation, gypsum wallboard, and vinyl wall coving. The veneer was supported on relieving angles bolted to the spandrel beams of the concrete structure. Window perimeter calking
1 Dual seals provide a sec- ond line of defense against water infiltration
Adhesion failure of sealant on stone.
right Roof flashing, Imperial Polk County Courthouse in Bartow, Florida
1 Initial design of flashing at roof transition was surface- applied to masonry wall 2 Revised detail of flashing was stepped to provide through-wall flashing to effec- tively weep water
Water leakage through the brick veneer wall occurred primarily at window openings and at roof-to-wall intersections. The transition details at the courthouse had four major prob- lems. First, the flashing material proved to have poor durability. Composed of PVC, the flashing material became brittle within three years of installation – particularly in areas where it had been folded or manipulated, the flashing began to split. Second, many of the window flashings failed to shed water to the exterior. In most cases, they did not extend all the way to the face of the veneer. Third, end dams were not provided at terminal edges, and the flashings did not turn up behind the window sill to prevent water from tracking back into the building. Finally, the flashing at the intersection of the brick veneer and the side (rake edge) of the sloped roof did not provide a through-wall flashing. Similar to the Vontz Center in Ohio, flashing of the sloped roof consisted of a metal termination bar sur- face- mounted to the face of the masonry wall. With no through-wall flashing to collect water flowing down the inside face of the cavity wall, water infiltration was inevitable. In order to stop the air and water infiltration that riddled this building, the entire brick veneer with its windows was removed. A rub- berized asphalt membrane was applied to the exterior face of the CMU back-up wall, and new copper flashings were installed around the entire perimeter of the window openings. The flashing system with an upturned leg was sealed to the window frames and the rubber- ized asphalt membrane was adhered to the flashings. In order to be effective, the flashing at the roof was installed in a step manner to follow the slope of the roof and the masonry mortar joints. The flashing was integrated into the mortar bed and head joints of the brick veneer. All the vinyl wall covering was removed from the interior face of the dry wall and replaced with a breathable latex paint. It was important to establish a vapor barrier on the warm side of the insulation (in this case, the outside was the warm side), and removal of the wall paper was necessary to prevent a double vapor barrier from trapping moisture within the wall system. After three years of work, remedial construction costs
were approximately two-thirds of the original building cost.
The cracking and bulging of the brick veneer at the courthouse was the result of ineffective and missing relieving joints in the brick façade. These cracks were the entry point for much of the water problems at the building. The original veneer lacked vertical control joints and horizontal expansion soft joints. These were installed in the replacement veneer. In order to better understand the ori- gin of the cracks at the Imperial Polk County Courthouse, one needs to understand the modes of differential movements in a veneer façade.
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right Imperial Polk County Courthouse, Bartow, Florida, 1986. Relieving angles with soft joints below each relieving angle and vertical control joints at approximately 6 –9m (20-30 feet) on center were installed with the replacement veneer wall.
below Imperial Polk County Courthouse showing revised stepped flashing completed with replacement veneer wall.