Best-Practice Wall Shingles
A rain screen offers the ultimate defense against water intrusion, provided you get the details right
by Mike Guertin
In the Ocean State — where wind-swept rains aren't restricted to nor'easters, tropical storms, and hurricanes — I count on a vented rain screen coupled with carefully detailed flashings to keep water out of walls.
A rain screen is a cladding system with a vent space (or a series of vent channels) between the back side of the cladding and the weather-resistive barrier. Openings along the top and bottom of the vent space let air flow freely. This vent space provides a channel for any water that gets past the cladding surface to drain out, and the air flowing through this space carries away moisture vapor that dries off the back side of the siding. In both instances, the vent space reduces the chance of water and moisture vapor being driven into the wall cavity by wind or sunshine.
Installing any cladding as a vented rain screen is the best way to make the cladding last. However, it's easier to do with lap sidings than with shingles. Lap siding, such as cedar clapboard and fiber-cement planks, easily bridges air channels between vertical furring strips nailed over studs. But a vented rain screen with sidewall shingles requires horizontal furring, which presents some complications.
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