What's the Best Way to Flash a Roof Against a Vertical Wall?

The transition where a flat or low-slope roof meets a vertical wall is one of the most common leak locations on commercial buildings. Here's how to seal it correctly.

Why Wall-to-Roof Transitions Leak

This transition is vulnerable because the roof membrane must make a 90-degree turn up the wall surface. Over time, thermal expansion and contraction stress the flashing at this angle. Traditional metal or bituminous flashings can crack, separate, or allow water to infiltrate behind them.

Traditional Flashing Methods

Standard approaches include metal counterflashing embedded in the wall, bituminous membrane flashing turned up the wall, and EPDM or TPO flashing strips. All of these create seams and attachment points that can fail over time.

Spray Foam: Seamless Wall Flashing

Spray foam is one of the best solutions for wall-to-roof transitions. Applied as part of a foam restoration, the foam flows up the wall face and creates a completely seamless, monolithic waterproof surface from the roof field through the transition and up the vertical surface. There are no seams, no attachment points, and no gaps for water to infiltrate.

Silicone Coating Reinforcement

For roofs being restored with a silicone coating system, the wall-to-roof transition is typically reinforced with fabric tape embedded in compatible sealant before the coating is applied over the top. This provides a flexible, reinforced waterproof transition that accommodates thermal movement without cracking.

The Bottom Line

Any restoration or replacement project should pay special attention to wall-to-roof transitions. A flashing failure at these locations will cause leaks regardless of how well the rest of the roof is performing.