Core TradesQuestion 207 of 700

For window head flashing to work correctly with a water-resistive barrier, the barrier above the window must be lapped so that it:

a.Tucks behind the flashing at the bottom edge
b.Is sealed only with caulk over the flashing face
c.Is cut away entirely above the window
d.Overlaps the top of the flashing in shingle fashion so water drains outward

Explanation

The weather barrier above the opening must lap over the top edge of the head flashing shingle-style so any water running down the wall is directed to the outside face. Tucking it behind, relying on caulk alone, or removing the barrier lets water get behind the flashing and into the wall.

Law Reference: 2025 CA Building Code, Chapter 14 (Exterior Walls)

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