Air and water can also infiltrate through, not around, windows. Often, leaks in the window assembly are caused by deteriorated gaskets, which are neoprene or butyl rubber seals that cushion the glazing and provide weather protection. Even if gasket deterioration is systemic, the windows may not have reached the end of their service life; there are options available to address failed gaskets without replacing the windows.
One option is gasket replacement, which involves removal of the existing perimeter gasket and installation of a new one. Because gaskets age better than sealants, gasket replacement is the preferred long-term solution. It is also more expensive. To install new gaskets may require removal of glazing, which is both disruptive and labor-intensive. Because of the age of some windows, replacement gaskets may no longer be available.
Where gasket replacement is not feasible, an alternative option is to cut out the top of the existing gasket bulb and apply elastomeric sealant. Although less expensive in the short term, this repair method creates an ongoing maintenance issue, due to the relatively short life expectancy of sealants. During installation, correct placement of sealant is important, both to ensure adhesion and to avoid blocking voids in the frame that allow moisture to exit the assembly.
Air and water infiltration through windows may also be the result of aging frames, which have developed cracks at welds and stress points. If deterioration is limited, such that the window is still structurally sound, it may be possible to retrofit the existing assembly, rather than replace it.
To protect against leaks and drafts, an additional layer of glass — a "storm" pane — may be added at the building interior. However, such installations tend to render formerly operable windows inoperable and may result in condensation problems if not carefully designed and installed. Interior storm windows are therefore usually considered temporary measures.
Another possible cause of leaks may be a poor seal between the operable and fixed portions of the frame. Depending upon the age and size of the windows, and the degree of deflection, these seal defects may or may not be repairable. As with gaskets, replacement parts for older windows may no longer be available.
Condensation is another sign of trouble with windows. Fogged glass is often caused by a breach in the seal of insulating glazing units. These double- or triple-glazed windows incorporate multiple glass panes separated by an air- or inert-gas-filled space. When seals in insulating glazing units fail, moisture can become trapped between panes. Depending upon the extent of the problem, it may be possible to replace the glass, while keeping the existing frame. However, if the window is also exhibiting other problems, it may be worth considering complete replacement.
To identify the source of condensation at the interior surface of windows, an investigation should consider when the problem occurs, and where. Does condensation develop only on the glass, or does it form on frames, as well? Often, condensation is a problem in historic buildings with metal-framed windows, where thermal separation between the building interior and exterior is minimal. Rather than replace poorly performing windows, the U. S. Department of the Interior recommends that historic windows be preserved whenever possible. Mitigating condensation on existing windows is usually achievable, but the restoration approach is best determined on a case-by-case basis.
All building components age and, eventually, reach the end of their useful lives; windows are no exception. Existing windows can often be repaired or modified to extend their lifespan, but at some point, replacement may be the preferred solution. Factors that might lead a facility manager to pursue window replacement include energy consumption, user comfort, aesthetics, and the cost of repair versus replacement. Knowing the basics of window design is important to being an educated consumer and making the best decision for the building and situation.
One key is to know the code. State and local codes dictate minimum requirements for building components, including windows. These requirements vary from one geographic location to the next, so window selection is seldom "one size fits all." For instance, whether the building is in a heating climate, where there are more calendar days when the building is heated than when it is cooled, or in a cooling climate impacts determination of the solar heat gain coefficient for the window assembly.
Codes often require that windows be designed to meet minimum requirements for wind and lateral forces. Structural requirements not only affect the selection of frames and the number of anchors, but also may stipulate fully tempered glass, rather than heat-strengthened or annealed.
Energy performance is also dictated by code. Facility managers looking to fulfill baseline code requirements without overspending stand to benefit from a familiarity with energy regulations; by selecting only those options that are necessary to meet code, facility managers can decline expensive extras that might be superfluous.
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