A.Luis De Miguel, senior researcher at the Canada Mortgage and Housing Corporation, responds: Venting the top of rain screen cavities is not recommended. Research has shown that when wind pressurizes one side of a house and depressurizes the opposite side, vents at the top of a rain screen or curtain wall can allow moisture to be sucked into the cavity. Vents at the top of a rain screen do not contribute appreciably to helping the cavities dry out. If the cavities are closed at the top, quicker pressure equalization is possible, and less water will enter the cavity.

The bottom of the rain screen cavities can be screened with insect screen or thin aluminum soffit vent, bent into a U-shape. The screen should be stapled to the sheathing prior to installing the vertical battens, and then later folded over the battens and stapled again.

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