Choosing high-quality, WDMA-certified windows is a smart investment for any homeowner or builder. These windows meet rigorous standards set by the Window & Door Manufacturers Association (WDMA) for performance, energy efficiency, and durability. However, even the best windows can fail to perform if not installed correctly. Improper installation can lead to water leaks, poor insulation, structural damage, and costly repairs.

To help you avoid common pitfalls, here are the most frequent mistakes made during the installation of WDMA windows, and how to prevent them.

1. Not Checking the Rough Opening

One of the most overlooked steps in window installation is failing to ensure that the rough opening is level, square, and properly sized. An uneven or misaligned opening can result in windows that don’t open or close properly, or worse, allow drafts and water intrusion. Always measure the height, width, and diagonals of the opening. Use a level to check for plumb and square conditions before placing the window.

2. Skipping Flashing and Waterproofing

WDMA standards emphasize proper sealing and water management. Skipping flashing tape, sill pans, or weather-resistant barriers can allow water to seep into your walls. Over time, this can lead to mold growth, wood rot, and insulation damage. Always install flashing along the sill and sides of the rough opening and follow the manufacturer’s recommendations for water management.

3. Improper Shimming

Shims are critical for ensuring that the window sits level and remains stable in the opening. Without correct shimming, the frame can warp, the sash may not operate correctly, and stress may be placed on the window, causing glass breakage. Place shims near the corners and at latch points, and always verify level and plumb before final fastening.

4. Using the Wrong Fasteners

Not all screws and nails are created equal. Using fasteners that are too short, too long, or not corrosion-resistant can compromise the structural integrity and void warranties. Follow the WDMA window manufacturer’s guide closely, and use fasteners that are designed for exterior use and capable of withstanding wind loads in your climate zone.

5. Over- or Under-Insulating Around the Frame

Too much expanding foam can bow the window frame, while too little insulation leaves gaps for air and moisture to enter. Use low-expansion foam or fiberglass insulation to fill gaps between the window and framing. Be careful not to compress or overfill, as it can affect the window’s function and appearance.

6. Ignoring the Manufacturer’s Instructions

Every WDMA window product is different, and each manufacturer provides specific installation instructions that are tested to meet performance ratings. Ignoring or guessing installation procedures can lead to non-compliance with local building codes, warranty issues, and compromised performance. Always read and follow the installation guide that comes with the product.

7. Failing to Check Operation After Installation

Once the window is installed, some installers fail to test it. You should always open, close, and lock the window multiple times after installation to ensure it works properly. Misaligned windows can bind, leak, or fail to lock securely—issues that should be caught and corrected immediately.

8. Not Sealing Interior and Exterior Gaps

Neglecting to seal both inside and outside gaps is a common error. Interior gaps can allow drafts and moisture into your home, while unsealed exterior joints are a direct path for water infiltration. Use high-quality caulking that is paintable, flexible, and weather-resistant to seal all joints after installation.

Conclusion

Avoiding these common mistakes during installation is essential to getting the full benefit of your WDMA-certified windows. Proper preparation, attention to detail, and adherence to WDMA guidelines can ensure your windows deliver the performance, energy savings, and durability they were designed for. If you’re unsure, consider hiring a professional installer who understands WDMA Windows and Doors and their unique requirements. A little care now can save a lot of trouble later.