TechNote - Window and Door Flashing: Code Requirements and Best Practices

Flashing at exterior windows and doors is critical for shedding rain water to ensure a dry and durable building. Missing or inadequately-installed flashing can lead to water intrusion, moisture damage to building materials, and indoor air quality issues. Resulting homeowner call-backs may be costly, requiring removal of finishes and even replacement of structural elements.

This TechNote provides an overview of building code requirements and best practices for flashing at window and door frames. The focus is on common flashing applications for new construction. Although each window/door manufacturer may have its own set of flashing instructions, the strategies and general principles apply to the vast majority of flashing situations.

There are two key principles for effective flashing at windows and doors to allow water to drain down the face of the wall and away from the building:

  • Integrate flashing with the water-resistive barrier (WRB), e.g., house wrap.
  • Install membranes shingle-fashion where the top layer of the WRB or flashing laps over the bottom layer to prevent water draining behind the bottom layer.