Flashing Exterior Doors is a crucial but often overlooked aspect of construction. While many builders prioritize flashing windows, exterior doors present a larger potential area for moisture intrusion and require equal attention. This article explores the importance of flashing exterior doors and outlines best practices for proper installation.
Why Flashing Exterior Doors Matters
Exterior doors, particularly those with minimal overhead protection like garage service doors, are highly susceptible to water damage. Without proper flashing, water can seep into the door frame, leading to rot, mold, and structural damage. A common misconception is that a porch roof or overhang provides sufficient protection. However, wind-driven rain can easily bypass these barriers, making flashing essential even in seemingly sheltered areas. Furthermore, flashing not only prevents water intrusion but also minimizes air and insect infiltration, improving energy efficiency and comfort.
The image above illustrates a common double standard: a fully flashed window adjacent to an unflashed exterior door in a protected area. Notice the absence of flashing below the door threshold; only a metal drip cap will be added later, offering insufficient protection. The potential leakage area of the exterior door significantly exceeds that of the window, highlighting the critical need for proper flashing.
Common Flashing Oversights
Many builders rely solely on a metal drip cap for flashing exterior doors, especially for garage service doors. This practice often stems from mimicking front door installations where a porch offers perceived protection. However, garage service doors frequently lack adequate overhead cover, leaving them vulnerable to moisture. Similarly, exterior doors in multi-unit buildings often face inconsistent protection, leading to a tendency to omit comprehensive flashing.
This image depicts a garage service door with inadequate flashing, exposing it to potential water damage. The lack of comprehensive flashing around the door frame creates vulnerabilities for moisture intrusion.
Even in covered areas, improper flashing can lead to problems. An exterior door located near the edge of a covered patio, for instance, remains susceptible to wind-driven rain. Inadequate flashing in such cases can allow water to penetrate the door jamb and threshold.
The picture above showcases an improperly flashed exterior door in a covered patio, highlighting the risk of water intrusion even in seemingly protected locations.
Best Practices for Flashing Exterior Doors
Implementing a comprehensive flashing program for exterior doors is crucial for ensuring a weather-resistant building envelope. This program should adhere to industry standards (AAMA, ASTM, NWWDA, WDMA) and manufacturer recommendations. Key steps for best practice flashing installation include:
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Threshold Flashing: Install self-adhered membrane flashing or a sill pan beneath the door threshold.
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Jamb Flashing: Apply self-adhered membrane flashing to both sides of the doorway, extending over the threshold flashing and at least 6 inches above the doorway opening.
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Door Installation: Install the door with compatible caulking beneath the threshold and around the back of the brick molding or trim.
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Drip Cap Flashing: Install angled metal drip cap flashing extending over the door head trim and returning at the ends.
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Head Flashing: Apply a self-adhered head flashing strip over the drip cap and extending at least 6 inches beyond the side jamb flashing.
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Weather-Resistive Barrier (WRB): Install the WRB over the head flashing, ensuring proper overlap and sealed seams. The WRB can be installed over or under the jamb flashing depending on the sequence.
This image demonstrates an improperly installed weather-resistive barrier, failing to adequately cover the head flashing strip, leaving a gap for potential water intrusion.
Conclusion
Flashing exterior doors is a fundamental step in preventing water damage and ensuring the longevity of a building. By adhering to best practices and industry standards, builders can create a weather-resistant building envelope that protects against moisture intrusion, air infiltration, and insect infestation. A consistent and comprehensive flashing program for all exterior doors, regardless of their perceived exposure, is essential for building quality and durability.
