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Successful window projects, whether they involve replacing or repairing windows in existing facilities or purchasing them for new construction, require careful planning. But some facility executives rush into window projects without fully understanding the impact that windows may have on facilities and operations. But mistakes made in selecting and installing windows may haunt the facility for 40 years or for whatever length of time passes before the window is replaced. Understanding these five common mistakes makes them easier to avoid and increases the chances of a window project proceeding painlessly.
One of the most basic mistakes made in existing facilities is to conclude windows need to be replaced without considering restoration of existing units. With the cost running only 25 to 30 percent that of replacement, restoration can extend the life of existing windows while providing many of the benefits of a replacement project. On a life-cycle cost basis, replacement often provides a much better rate of return for the investment.
All windows deteriorate. Components rot, corrode, warp and wear with time and exposure. Gaps between components form, resulting in increased energy losses. Surfaces deteriorate, changing the appearance of the windows.
If the deterioration is sufficient, then replacement is the best option. But the decision to repair or replace should be based on a proper assessment.
Start with the condition of the existing windows. What repairs are needed? Are repairs minor or extensive? Is the structural integrity of the windows an issue? If the windows are operable, can they be opened and closed easily? Do they require support when opened?
As a rule of thumb, if more than 20 percent of the windows require restoration, replacement may be the better option. Other factors must be considered, such as the suitability of the existing windows for the current and planned functions of the facility and the cost to maintain the existing vs. replacement windows. But jumping to the conclusion that the windows must be replaced just because they look bad or are old may result in unnecessary expenses.
Windows have been so widely promoted for their impact on energy use that it is generally accepted that replacement windows will dramatically cut energy costs, enough to recover the cost of the replacement project in “just a few years.” Some manufacturers and installers claim that window replacement can provide 25 to 30 percent energy savings.
Energy savings of this magnitude tend to get the attention of everyone. But this is not a 25 to 30 percent reduction in the total energy bill. Rather, it is a reduction in the energy loss through the windows. Compared to total facility energy use, the percentage savings in most facilities is fairly small.
While the energy savings produced by replacing older windows is significant and important, the relatively high cost of the installation results in a long simple payback period, one typically ranging between 15 and 25 years. For this reason it is rarely possible to justify the cost of a window replacement project solely on the basis of energy savings. Many other energy-related projects will provide a quicker payback. That does not mean that windows should not be replaced. Replacement windows will produce other savings and benefits. But facility executives should be wary of overly optimistic savings projections.
Just as the energy impact of window replacement projects is often overestimated, their maintenance impact tends to be underestimated or overlooked. For properly selected and installed windows, over their service life, the savings from reduced maintenance typically exceeds the energy savings.
The actual savings produced will depend on the type and condition of the existing windows as well as the type of replacement windows installed. Before selecting a replacement window, identify what maintenance activities are being performed on a regular basis on the existing windows. If the existing windows have wood frames, chances are they must be painted every five or six years. Selecting a clad frame will eliminate this maintenance cost.
If the windows are cleaned on a regular basis, consider installing units that tilt or pivot for cleaning from the inside. Cleaning costs can be further reduced by selecting other options, such as removable muntin bars or muntin bars installed between the layers of glass. Over the life of the window, the savings from this option alone will be very significant.
Until the widespread use of air conditioning, operable windows were standard. The widespread availability of central air conditioning led many facilities to use fixed windows. When the energy crisis of the 1970s hit, the fixed window essentially became the standard.
Since the late 1970s, there has been a running debate as to which configuration, operable or fixed, is more energy efficient. Operable windows allowed occupants to use outdoor air for ventilation. But operable windows also could increase heating and cooling loads if windows were opened when the central systems were operating.
Fixed windows prevented this problem, but also required that central heating or cooling equipment be used at all times. Fixed windows also resulted in hot spots on the south side of buildings during times when the remainder of the building did not require air conditioning and the central air conditioning equipment was shut down.
Today, another factor in the operable/fixed window debate must be taken into consideration: security. Windows affect security in two ways. They keep things inside the building, and they keep people and things outside. Operable windows increase security risks. While there are options, such as grates and security screens, that can be used to improve the security of facilities with operable windows, they will affect the appearance of the facility.
Before selecting fixed or operable windows, the facility executive should evaluate the needs of the facility. Will operable windows allow the run times of central air conditioning equipment to be reduced? Are the central systems designed to take advantage of operable windows? What are the security concerns of the facility relative to the windows? Will operable windows result in a threat to building occupants and contents? Only after evaluating these concerns should the issue of operability be decided.
Just because a window meets building code requirements for energy conservation is no indication that the window is the most energy-efficient unit for an application. Three energy conservation factors must be evaluated when considering new or replacement window options: U-factor, solar heat gain coefficient and visible light transmission.
A window’s U-factor is a measure of its thermal conductivity. The lower the U-factor, the lower its thermal conductivity and the higher its resistance to heat gain during the cooling season and to heat loss during the cooling season. Look for the lowest U-factor. While U-factor is important in all locations, it is particularly important in northern locations.
Windows are a major source of solar heat gain. This heat gain, while slightly reducing the building’s heating requirements, is a major contributor to the cooling load. Tints and coatings can be applied to the glazing to reduce the solar heat gain. Controlling solar heat gain is most important in middle and southern climates. Even in northern climates, controlling solar heat gain is important in buildings having large areas of glass. Look for windows with low or medium solar heat gain coefficients.
The color and tint applied to windows also will affect the visible light transmission of the glass. While the most obvious impact is the external appearance of the building, changes in visible light transmission will also affect security. Low visible light transmission factors make it difficult for those outside the facility to see into the building during daylight hours. They also make it difficult for those inside the building to see outside during night operations. Before selecting windows that limit visible light transmission, consider the impact on operations and security.
Windows have an effect on the facility and its occupants that goes beyond factors that can be easily measured, such as energy and maintenance costs. But the intangibles are important. Two of the most important are comfort and aesthetics.
Windows that do not properly seal allow air to infiltrate the building, creating spaces that are hot, cold or drafty. Clear glazings, particularly those located on the south side of a building, can create hot spots even during the heating season. Stuck windows cannot be opened to provide ventilation or natural air conditioning.
The net result of all these factors is discomfort. Create enough discomfort, and building occupants may become dissatisfied enough to decide to look for other, more comfortable space.
Walk the building during both the heating season and the cooling season. Talk to occupants in the perimeter areas, particularly along the building’s south facade. How consistent do temperatures remain from interior to exterior spaces? Are there hot spots or drafty areas? If so, identify the source. If it is the windows, that’s another reason to consider replacement.
Finally, windows have a major impact on the overall appearance of a building. The color and type of the glazings, the color and shape of the frames, and operability all will determine how the building appears. While the appearance of a building is difficult to measure and evaluate, it is an important intangible factor, especially in leased space where it may make the difference between a tenant selecting one facility over another. If there is any question as to how a replacement window will influence the appearance of a building, consider installing a test window or having an image of the building created to reflect the appearance of the new windows.
By avoiding these common mistakes in window selection, facility executives can help to ensure that an investment in windows will be one that provides a maximum return.
James Piper, PhD, PE, is a writer and consultant who has more than 25 years of experience in facilities management. He is a contributing editor to Building Operating Management.