Window replacement is one of the most popular—and most lucrative—home remodeling projects. In fact, Remodeling’s 2017 Cost vs. Value report indicates that vinyl and wood replacement windows offer a 73.9% and 73.0% return on investment, respectively, ranking among the 10 projects with the highest returns.

Perhaps more importantly, replacing old, leaky windows can have a big impact on energy costs, as well. According to the Department of Energy, replacing old windows with ENERGY STAR® certified units can lower a home’s energy bills by an average of 12% while helping to reduce the built environment’s carbon footprint.

ENERGY STAR® certified units are independently tested to verify that they meet certain performance levels in five areas: U-factor (amount of heat transfer), solar heat gain coefficient (indicates how well the unit blocks heat from the sun), air leakage (through the window joints), visible transmittance (how much light gets through), and condensation resistance.

But no matter how much more robust and efficient the replacement window is, its efficiencies will be for naught if the unit is not installed properly. Poor installation in new construction or remodeling can lead to air leaks that drive up energy costs or moisture intrusion that can lead to mold and indoor air quality issues while decreasing the durability of the entire wall cavity.

Keep in mind that windows are very different than they were 50 years ago. Most notably, they’re more tightly constructed; designed to keep air infiltration at minimum levels. Putting newer windows into older homes that were designed to breathe and dry out will change how that building works. You will need to consider how that shifts the mechanics of other areas of the house. For example, the sizing of HVAC. How does the building breathe and dry? Does the original home have housewrap? If not, how will you integrate the window with the wall to avoid air and moisture intrusion?

Along with installing windows “square, level, and plumb,” proper installation of window flashing and integration with the existing drainage plane is most critical to prevent air leakage as well as avoid moisture intrusion.

Turn to your manufacturer as a resource and follow all installation instructions. The latest version of the ENERGY STAR® program requires that certified window products include instructions for installation, including proper flashing techniques, for building envelopes with and without a weather resistive barrier already in place.

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