How to Know When Windows Should Be Replaced
The performance of the overall exterior wall assembly is not just dictated by window selection, but how one details the wall around those windows.
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On average, how often should windows be replaced in a facility and what are some tell-tale signs that windows need to be replaced?
Bailey says that the life span of windows will generally vary based on the conditions in which the windows are exposed to, and the level of detail provided to help protect from the failure of those windows. For example, the performance of the overall exterior wall assembly is not just dictated by window selection, but how one details the wall around those windows.
“Window selection along with great detailing and maintenance should allow the glazing assembly to see 30-plus years,” Bailey says. “However, the wall is only as strong as its weakest link.”
NFRC certifies products for U-factor, solar heat gain coefficient (SHGC), visible transmittance, air leakage, and condensation. Though a required rating for Energy Star, air leakage is otherwise an optional rating; condensation resistance is also an optional rating that will soon be replaced by a more useful (but still optional) condensation index. U-factor and SHGC are the ratings referred to in energy codes.
According to Callahan, U-factor is the largest factor in heat loss in winter while SHGC can actually provide free heat. In the summer, both the U-factor and SHGC are a measure of heat gain, but SHGC is the driving factor.
“Location determines whether U-factor, SHGC, or a combination of both are the focus for comfort,” Callahan says.
Many organizations provide certifications for structural performance. The Fenestration and Glazing Industry Alliance (FGIA), Keystone Certifications, Inc., National Accreditation & Management Institute, Inc (NAMI), and the Window and Door Manufacturers Association (WDMA) provide fenestration certifications.
“There are no tests available to check the performance – energy or structural – of a window on-site, however, an occupant or building manager can check for obvious signs of damage, test for air leakage and drafts, and question occupants on comfort,” Callahan says.
Some tell-tale signs that windows need to be replaced can be caused by any of the following:
- Condensation between glass panels
- Clouding or fogging
- Breakage (impact or weather/temperature related)
- Operational issues or failure of frame(s) and hardware.
- Dried/cracked seals
- Missing sealant, or visible deterioration of sealants
- Noise (as heard through broken seals)
And remember, energy code (U-Value) targets for buildings can vary, and those targets will inform what types of materials to implement.
Bailey suggests that if facility managers are looking to exceed the energy code, triple-glazing is a great option.
Those in inclement weather locations, including in hurricane prone areas, will want to use laminated glass that can withstand abrasive weather. Security and vandal-resistant glass is also a component designed to withstand the elements.
“Think of your glazing as a series of layers, and how those layers are chosen will affect the overall performance,” Bailey says. “Those layers should be selected based on a variety of environmental factors.”
Various coatings (low-E/reflective) and compositions are possible, so each project should undergo an analysis (energy modeling) to best determine the composition of the windows needed.
From an aesthetic standpoint, various colors, patterns, and sun-shading devices will also contribute to the performance of the glazing system. Changing the VLT of the glass can alter the look and performance of the system, while helping to control heat gain.
“Also, unitized curtain wall versus stick-built curtain wall has pros and cons that should be evaluated on a project-by-project basis to consider cost, schedule, and performance,” Bailey says. “It’s more than just picking the window. In a new or existing building, the exterior wall assembly as a whole must be studied. The window is just one key component of that assembly. If any other aspects of the assembly fail, the energy efficiency of the building would be compromised. From a maintenance perspective one will want to know how maintenance of the window assemblies could affect the warranty and longevity of the product.”
And for windows that are to be replaced immediately, ensuring that products purchased meet – and exceed when possible – building and energy codes should provide building managers and occupants with the assurance that they have met all known requirements.
Callahan points to the Efficient Windows Collaborative website, a consumer education program for NFRC, that provides information on what to look for when purchasing windows and consumers shopping for windows can match products available in their areas with their local codes through the Window Selection Tool.
“Though designed for single family homes, it may provide valuable information for those purchasing windows for larger buildings as well,” Callahan says. “In addition, the importance of good installation can’t be understated. A poorly installed window can result not just in drafts and air leakage, but it can also lead to safety concerns, substantial building damage if water is able to penetrate the wall, and voided warranties. Manufacturers may recommend installers for their products, and there is a list of certified installers in the U.S. available from InstallationMasters.”
Also, make sure that any claims about performance are backed by certifications from NFRC for energy performance, and AAMA/FGIA, Keystone, NAMI, or WDMA for other code requirements. These certifications provide assurance that any comparisons between products and manufacturers are tested and reported the same for each product, for an apples-to-apples comparison.
“Be aware that cutting costs on the front end may increase costs after installation, either through higher utility costs, through retrofits to bring the building to code, and even through lower tenant satisfaction,” Callahan says. “According to research by the American Council for an Energy-Efficient Economy (ACEEE), providing potential renters with information on the energy efficiency of a building, resulted in renters choosing the efficient listing 21 percent more often than buildings without energy information.”
Maura Keller is a freelance writer based in Plymouth, Minnesota.