The more air that moves behind the siding, the more drying capacity the assembly has.
When we install vertical strips of solid material behind the siding, we create small cavities. These cavities may not connect to the outdoor air except at the bottom and won’t dry nearly as well as cavities that have vent openings at the top or spaces that connect laterally and allow air and moisture to move in all directions. Similarly, narrow spaces won’t allow as much air movement and drying as wider spaces.
As risk levels rise, we should consider moving from tiny, 1/16-inch spaces provided by textured wraps up through 3/16- to 1/4-inch gaps from mesh or strip products, up to full 3/4-inch spaces created by 1-by lumber strips.
Venting at the tops of walls can be added with corrugated vent products hidden between pieces of trim, as shown in the illustration at right. We’ve found these vents to be unobtrusive and easy to build.
One caution: I’ve seen discussion online about connecting wall vent cavities to roof vent spaces. I don’t think this is a good idea for two reasons: First, I think it increases fire and insect hazards and probably doesn’t meet the intent of code provisions, which call for wall cavities to be cut off from roof cavities. Second, at least in my climate, wall cavities can have huge moisture loads that we don’t want to put into the attic.
One of the reasons I like drain-mesh products is they allow lateral, as well as vertical, air movement. This provides much more air movement and drying ability for any water that gets in at any spot in the wall.
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