When installing step flashing at a roof-to-wall intersection in California, what is the minimum overlap requirement for each piece of step flashing?
Correct Answer
D) 4 inches
CBC Section 1507 flashing requirements specify that step flashing pieces must overlap each other by a minimum of 4 inches. This ensures adequate water protection at critical roof-to-wall intersections, preventing water infiltration that could cause structural damage in California's varied precipitation patterns.
Why This Is the Correct Answer
CBC Section 1507 specifies a minimum 4-inch overlap for step flashing pieces at roof-to-wall intersections. This dimension ensures that water running down the wall is always directed onto the flashing below it, not behind it, providing reliable protection against infiltration.
Why the Other Options Are Wrong
Option A: 6 inches
6 inches is the common minimum for headlap in asphalt shingles, not for step flashing overlap. Confusing shingle headlap with step flashing overlap is a typical error; the two are governed by different provisions.
Option B: 2 inches
2 inches is insufficient overlap for step flashing and does not meet CBC requirements. Such a small overlap would leave critical gaps during heavy rainfall or when the wall moves slightly under load or thermal expansion.
Option C: 3 inches
3 inches is below the code minimum of 4 inches. It may seem reasonable as a midpoint but does not satisfy CBC Section 1507 and would not pass inspection.
Memory Technique
Four fingers = 4 inches of flashing overlap. Hold up four fingers and imagine pressing them against the wall — that's the minimum physical barrier the flashing must create.
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