The window and curtain wall system has evolved over the years, especially with respect to weather control. Each has its own unique challenges and is designed to respond to different performance requirements when controlling the passage of air and water. The glazing components used to seal and support the glass or metal panels, however, all have anticipated performance life cycles and will eventually need either repair or replacement. To complicate matters, many of the glazing components used in the past may have compatibility issues with adjoining sealants used today. Butyl sealants that were prevalent 20 years ago have now been replaced with silicone sealants, which may not be compatible with components used in today's repairs.
When failures occur over time, restoring integrity to these systems can be extremely challenging. Large, commercial buildings are occupied and disruption must be minimized. Total replacement is cost-prohibitive, time-consuming and extremely disruptive so alternative solutions must be explored. Repairs should also be considered when designing the initial window or curtain wall system to ensure cost-effective maintenance.
Frequently, the solution selected for repairing window systems is a cap bead to renew the appearance and restore the weatherseal performance. Silicone sealants can provide a continuous weatherseal and restore aesthetic appeal but are dependent on workmanship and have an affinity to attract dirt. Sealant cap beads are not a solution when the face clearance is small, which results in high shear forces on the cap bead, or when there is insufficient metal surface contact area for the sealant to bond.
Custom gasket overlays is another alternative that may be used to restore performance to badly weathered, structurally sound windows while reducing air leakage to improve energy efficiency. It has been estimated that each CFM of air leakage results in $3-$5 in energy costs. Custom gasket overlays developed by Tremco's design engineers may be used to clad or bridge existing gaskets and/or tapes to restore the weatherseal and provide a "like new" appearance. The overlay may also be designed to stretch to accommodate movement, and silicone gaskets do not attract dirt. With tax breaks for the thermal efficiency of buildings in some areas and the potential for paybacks in energy savings within a few years, this is an increasingly more attractive alternative.
Each of these restoration methods was put to the test at Tremco's Sustainable Building Solutions Test Facility to evaluate their ability to control air and water leakage. This testing program was designed to test window units as received from the factory, introduce leakage to establish a baseline to compare the restorative results against, and then test each restoration practice for air and water leakage. Testing for air leakage was performed in accordance with ASTM E283 and testing for water leakage was performed in accordance with ASTM E331 or ASTM E547.
Both the cap bead and custom gasket overlays performed well in the Tremco test chamber. The testing does not incorporate wind loads or stack effect, though. Higher elevations have higher wind loads and greater movement that will impact performance over time. Air leakage could be ten times higher when these factors are considered and, therefore, energy savings would be significantly higher. Restoration of glazing systems to remedy water intrusion, improve energy efficiency, correct improper installation, restore performance lost due to aging components or renew aesthetic appeal requires investigation to develop the appropriate option. Contact your local Tremco Sales Representative to review the building issues that may be contributing to problems, evaluate recommended options for repair and provide assistance with taking field measurements and interfacing with our broader support team.
Glazing Restoration Test Report
Restoration of window and curtain wall systems can result in substantial energy savings across a variety of climate zones. Retrofit measures can achieve performance results comparable to new replacement windows when put to the test - without the cost and disruption of window replacement. The AA900 punched window from Kawneer was selected for testing as being representative of common systems with small face clearance. Typically, small joints fail over time due to movement. To ensure a restoration alternative capable of withstanding thermal and structural movement, the overlay system was tested in addition to the frequently used cap bead. The cost of the overlay would be a fraction of the cost of typical window removal and replacement.
In addition to reduced operating costs due to the increased energy efficiency, there are LEED points that may be available for energy efficiency for restoration and the innovative ideas section for new construction or restoration. There are also tax breaks for thermal efficiency of buildings.
Each glazing restoration project is different with different solutions, but the return on investment can be substantial. Taking the case of a 600,000-square-foot, 45-story, Class A office building in New York City, it is estimated that the reduction in air leakage, when done as part of a Whole Building Air Barrier Continuity Study as conducted by Canam Building Envelope Specialists, could generate $60,000 in energy savings per year. In addition, the building owner was eligible for $360,000 in tax deductions ($.60/sq. ft.) under the Energy Policy Act of 2005 (EPAct 2005), as well as New York State Energy Research and Development Authority (NYSERDA) rebates for cost-effective energy efficiency improvements, dramatically reducing the time for payback.
Contact your local Tremco sales representative to find out how to transform your built environment into a high-performance environment.