Static structures (e.g. – buildings) – Wall – ceiling – floor – or roof designed for ventilation or...
Reexamination Certificate
2002-09-06
2004-11-30
Friedman, Carl D. (Department: 3635)
Static structures (e.g., buildings)
Wall, ceiling, floor, or roof designed for ventilation or...
C052S302300, C052S302700, C052S003000, C052S097000, C052S015000
Reexamination Certificate
active
06823633
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to water drainage systems for buildings, and more particularly to a secondary water drainage system for buildings which are constructed using pre-manufactured exterior panels or cladding, such as Architectural Precast Concrete (“APC”), Glass Fiber Reinforced Concrete (“GFRC”), Composite Architectural Precast (“CAP”), or Natural Stone on a Truss Frame system (“NSTF”).
2. Description of the Prior Art
Modern mid to high rise building are predominately constructed from a structural steel or cast-in-place concrete framework, upon which all other building elements are mounted and supported. For example, walls, floors, and electrical, plumbing, and HVAC systems are all integrated with and attached to the steel or concrete supporting structure. The exterior of the supporting structure is typically covered with the above-referenced pre-manufactured panels or cladding. Other common exterior coverings include glass, curtain wall systems, metal panels, stucco, Exterior Insulation Finish Systems (“EIFS”), plaster, and brick. All such exterior coverings must be carefully designed, constructed, and installed to comply with existing building specifications respecting air and water infiltration.
Exterior panels and cladding, being of a discrete size, have vertical and horizontal joints between adjacent panels. These joints must be sealed against air and water infiltration. For that purpose, high performance elastomeric sealants have been developed. The term elastomeric refers to a material's ability to compress or elongate when a stress is applied, and return to its original state when the stress is removed. These elastomeric properties are necessary to accommodate joint movements resulting from thermal expansion and contraction, inter-story building drift owing to wind forces or seismic movement, or elastic frame shortening and creep. State of the art elastomeric sealants exhibit high tolerance to joint movement, being able to accommodate movements on the order of plus or minus 25% of the joint's transverse dimension.
Silicone-based elastomeric sealants are commonly used to protect exterior panel or cladding joints from water intrusion. The manner of installation of the sealant is straightforward, but certain precautions must observed. The sealant is typically installed over a backer rod, made of polyurethane or polyethylene foam. The backer rod is initially installed along the full extent of the joint between the panels. Then, the silicone sealant is applied into the joint, against the side edges of the panels and the backer rod. The backer rod supports the sealant until it has fully sealed, and also ensures that a proper joint configuration is formed which will allow the sealant to expand and contract as required. The combination of the exterior cladding with the silicone sealant in the joints, forms the primary waterproofing barrier for the building.
The quality of this primary waterproofing barrier is highly dependent upon the skilled workmanship of the installer. For example, the installer must properly detail the bond line of the joint, by cleaning the opposing side edges of the adjacent panels so the sealant will properly adhere to the panel. The location and depth of the backer rod must be correct, to ensure that the sealant joint will have sufficient flexibility and resiliency to withstand expansion, contraction, and flexure forces. The integrity of the waterproofing barrier is also contingent upon the consistency, quality, and selection of the particular sealant used. The sealant which is most appropriate in an architectural precast concrete panel-to-panel joint, for example, may not be the proper sealant for an architectural precast concrete panel to an aluminum window mullion joint.
A failure of the waterproofing barrier can also occur when the exterior panels themselves are cracked or damaged, allowing water to pass directly through the panels. Failures in the barrier may occur at the interface between the glass and the curtain wall systems. The passage of time, including deterioration of materials, extreme temperatures, exposure to the sun, and seismic events, may all contribute to a joint failure or some other compromise in the integrity of the waterproofing barrier. Unfortunately, failure or compromise of the primary waterproofing barrier can occur with little or no warning, causing water or air intrusion.
When water leaks do occur, the damage caused to the building can further be amplified by percolation. Percolation arises when sustained high winds, or a positive external pressure caused by the operation of the building's HVAC, can literally vacuum water through the damaged sealant joints or cracked cladding. The water then bubbles or percolates into the building, causing more damage.
Another source of concern derives from condensation on the rear or backside of the panels. Sealants in the joints protect the interior region of the panels from leaks, but do nothing to protect against condensation. Under certain atmospheric conditions, water can condense on the backside of the panels even where no joint leak or panel cracking has occurred. The occurrence and extent of such condensation varies with the geographical location of the building, the type or lack of a vapor barrier, and the amount and temperature of the air infiltration into the building. When these factors favor the formation of condensation, the airspace between the panels and the supporting structure reaches 100% relative humidity. As the panels cool, condensation forms on their backsides.
Buildings also contain varying amounts of incidental moisture, resulting from small amounts of moisture which transmigrate through the panels or cladding. This occurs as a consequence of undetectable imperfections in material and workmanship. Most of the time, the leaks or condensation which produce this incidental moisture are so insignificant that the incidental moisture is absorbed by the substrate of the panels, and dries prior to any damage occurring. However, if the incidental moisture content exceeds the threshold saturation capacity of the substrate, the excess moisture may lead to interior damage to the building and promote mold growth.
The prior art teaches a number of different backup or secondary drainage systems to remove water or condensation from the rear side of exterior panels or cladding for modern buildings. For example, in Rizza, U.S. Pat. No. 5,289,664, a back drainage system for exterior panels is disclosed. An open gutter extends along the back wall of a panel, and includes a weep tube at one end extending toward the front wall of the panel. A piece of reticulated foam within the weep tube is claimed to allow water to flow out, while preventing moisture backup through the tube and wind noise. In U.S. Pat. No. 4,924,647, granted to Drucker, an exterior wall panel drainage system is shown. Gutters collect water from the rear wall, and drain tubes and weep holes drain the collected condensation to the outside of the panel wall. U.S. Pat. No. 6,216,406, issued to Smith, shows a mounting and draining system for prefabricated building panels. A drain tube extends between an interior gutter and the exterior of the panel. U.S. Pat. No. 5,048,254, granted to Merlau, shows a tapered base plate for collecting water trapped behind the building panel. The water in channeled through drainage holes into weep holes, and thereafter passes outside the building panel.
It is evident from the foregoing prior art that the industry recognizes the problems associated with rear panel condensation and water intrusion resulting from a failure of the primary waterproofing barrier. However, there is considerable room for improvement in the secondary drainage systems developed thus far. For example, percolation back through the drainage lines or weep holes of the prior art drainage systems, is a persistent problem. Prior art systems lack physical and installation flexibility, making them difficult to adapt to a variety of different pan
Amiri Nahid
Clark Pacific, A General Partnership
Friedman Carl D.
West R. Michael
LandOfFree
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