When discussing building envelopes, products like weather-resistive barriers, insulation, and exterior cladding often receive the most attention. Yet one of the most important components is frequently hidden from view: flashing.
Flashing may not be the most noticeable part of a wall assembly, but it plays a critical role in directing water away from vulnerable areas of a building. When integrated with the rest of the building envelope, flashing helps ensure incidental moisture is safely managed before it can reach structural components.
What Is Flashing?
Flashing is a material installed at transitions, openings, and penetrations where water is most likely to enter the building envelope. Common locations include:
- Windows
- Doors
- Roof-to-wall intersections
- Deck attachments
- Utility penetrations
- Wall transitions
Rather than stopping water completely, flashing is designed to collect and redirect it toward a safe drainage path.
Why Transitions Matter
Large wall surfaces generally perform well because they are continuous. Problems are more likely to occur where materials change or where the wall is interrupted.
Every window, door, vent, and penetration creates a transition that must be carefully detailed. Without properly installed flashing, water that bypasses the exterior cladding may find a path into the wall assembly.
This is why many building envelope failures begin around openings—not across the middle of the wall.
Flashing Works With the Weather-Resistive Barrier
Flashing should never be viewed as a standalone product. Instead, it functions as part of the overall moisture management strategy.
When integrated correctly with a weather-resistive barrier, flashing directs water onto the face of the WRB, where gravity carries it downward toward the drainage plane and out of the wall assembly.
Each component relies on the next. Flashing collects the water. The WRB manages it. The drainage layer provides a path for it to exit.
Sequencing Is Everything
Proper sequencing is one of the most important aspects of flashing installation. Components should overlap in a way that encourages water to flow downward naturally.
This “shingle principle” ensures that each layer sheds water onto the layer below it rather than allowing moisture to migrate behind the assembly.
Even high-quality materials cannot perform as intended if they are installed in the wrong sequence.
Where ALTA® Fits
ALTA® 360 is designed to work alongside properly detailed flashing systems as part of a complete building envelope.
Its drainable, vapor-permeable weather-resistive barrier helps create a continuous drainage path behind the cladding, allowing water collected by flashing to continue moving safely out of the wall assembly.
Together, flashing and ALTA support a building envelope that manages moisture through coordinated system design rather than relying on any single component.
Building Envelope Performance Is a Team Effort
No single product protects a building on its own. Long-term durability depends on how each component works together to control water, air, vapor, and heat.
Flashing is one of the smallest visible parts of the wall assembly, but it often performs one of the biggest jobs. When integrated correctly with weather-resistive barriers, drainage layers, and other control layers, it helps buildings remain durable, efficient, and resilient for years to come.
Looking Ahead
In Part 6 of our Building Envelope Basics series, we’ll explore common building envelope installation mistakes and discuss practical ways builders can help improve long-term wall performance through proper detailing and system continuity.