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What Causes Water Intrusion Around Windows

By Central Coast Building Diagnostics · June 5, 2026

Flashing, not the window itself, is usually the issue

Most window water intrusion traces back to how the window was flashed and integrated with the surrounding wall — not a defect in the window unit.

Common failure points

Missing or improperly lapped flashing, sealant used in place of proper flashing, and sill pans that weren’t installed or were installed incorrectly are frequent culprits.

Stucco and cladding interactions

Where stucco or other cladding meets a window, the transition detail is a common point of failure, especially on older construction.

Why it often shows up later

Sealant-dependent details can perform fine initially and fail years later as materials age and move — which is why older buildings often develop new window leaks without any recent damage to the window.

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