The Use of 4″ x 4″ Step Flashing: Ensuring Proper Roof Installation

What Is the Concern?

For asphalt shingle roofs, proper step flashing is crucial to prevent water infiltration and ensure the longevity of the roofing system. GAF’s standard step flashing instructions require step flashing to extend a minimum of 5 inches (127 mm) up the wall and a minimum of 5 inches (127 mm) out onto the shingles on the roof. The flashing must also be at least 2 inches (51 mm) longer than the exposure of the shingles being installed.

Alternative Step Flashing Size

While the preferred size for step flashing is 5″ x 5″, an alternative size of 4″ x 4″ is acceptable under specific conditions:

• Minimum Extension: The step flashing must extend a minimum of 4 inches (102 mm) up the wall and 4 inches (102 mm) out onto the shingles on the roof.
• Length Requirement: The flashing must be a minimum of 2 inches (51 mm) longer than the exposure of the shingles being installed.

Conditions for Using 4″ x 4″ Step Flashing

The use of 4″ x 4″ step flashing is acceptable only when a full 36-inch (914 mm) width of leak barrier (StormGuard® or Weather Watch® Leak Barrier) is installed at the wall to roof deck transition. This leak barrier must extend a minimum of 5 inches (127 mm) up the wall to ensure adequate protection against water infiltration.

Importance of Proper Step Flashing

Step flashing is critical at all roof-to-sidewall transitions to create a watertight seal. Properly installed step flashing helps prevent leaks, which are often the number one cause of roof damage. Flashing must be manufactured with non-corroding metal to ensure durability and long-term performance.

Conclusion

Ensuring proper installation of step flashing, whether using the standard 5″ x 5″ size or the alternative 4″ x 4″ size, is vital for the longevity and performance of your asphalt shingle roof. Following GAF’s guidelines and installing a leak barrier at the wall to roof deck transition can help protect your home from water damage.

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Disclaimer: This article is intended for informational purposes only. For professional advice, consult experts in the field.