While properly installed housewrap is a good start, building scientists recommend including a rainscreen under wall cladding for the best protection against water intrusion. Rainscreens are typically installed as vertical strips that are fastened to the wall to which the siding is fastened. The thickness of the strips holds the siding away from the housewrap and the sheathing underneath.
To install a separate rainscreen, cover the sheathing with any quality housewrap; it's not necessary to use one of the textured wraps discussed in my last post. I've also used taped Zip Wall sheathing with a rainscreen.
There are lots of different materials you can use to form a rainscreen, including 1x3 solid wood strapping, or ripped strips of HardiePlank for walls covered with that product.
My favorite rainscreen material is Coroplast, a two-layer recycled-plastic sheet product that's sold in 4x8-foot sheets and used mainly by sign makers and print shops. The outer layers of the product are held apart by parallel flutes that give the material thickness and rigidity. The flutes are continuous along the product's 8-foot length. Coroplast is available in various thicknesses; for rainscreens, I use 3/8-inch-thick Coroplast.
The material is easy to rip into strips on a table saw, though I buy it from my sign supplier already cut into 2-inch strips.
For the top and bottom of a wall, we use other, 3-inch-wide strips with the flutes running vertically, which allows convective ventilation behind the siding at the top of the wall and water drainage at the bottom of the wall. Before installing the top and bottom strips, we staple on an 8-inch-wide strip of insect screening, then fold it back over the Coroplast to keep out bugs.
You can also use Coroplast as a rainscreen for vertical siding by attaching the strips horizontally. You'll need to rip the Coroplast sheets across their 4-foot width and attach them so the flutes run vertically to allow water to drain through them.
For houses with a reservoir cladding—that is, stucco, stone, brick, or any cementitious product that is going to soak up lots of water—I use a zero-perm product, Delta-Dry Stucco & Stone. It's a 3/8-inch-thick dimpled plastic mat that's stapled to the housewrap. The exterior side of the product has a built-in mortar screen that prevents scratch coats from filling the dimples. The beauty of Delta-Dry is that it provides an air gap on both sides—between it and the stucco and between it and the sheathing.
For the ultimate protection on walls, there is another category of weather system that includes fluid-applied membranes and peel-and-stick membranes. Unlike some other barriers, these products have the added benefit of air-sealing a wall, as well as protecting it from moisture. Both should be used in conjunction with an installed rainscreen.