Louver boards

the sloping boards set to shed rainwater outward in openings which are to be left otherwise unfilled; as belfry windows, the openings of a louver, etc.

See also: Louver

References in periodicals archive ?
It was constructed with siding composed of connected cartwheels, V-cut type planks, shiplap paneling, louver boards, with a steep, cone-shaped roof topped with a cross.
They nailed the 1-by-4s to 4-by-4 posts and 2-by-4 horizontal crosspieces, and slipped in 1-by-3 louver boards from the back side.