Vent louvers (also called slats) are usually made at a 45 degree angle for rain to run down and stay outside the attic. The design is simple yet proven to be very effective over the centuries. The face or front of the louver acts as a stiffener to help brace against high winds. The louver then rises as it goes back for any rain collectd to run down. Then the rear is turned up so blowing rain will also be blocked.

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