Today Lab Notes returns to the FPL publication Installation, Care, and Maintenance of Wood Shake and Shingle Siding and discusses a method for installation.The rain-screen method of building construction gives a secondary barrier and drainage plane for water. Sheathing is placed over the studs and a water-resistant barrier (usually Type 30 felt) is applied. Although the shakes and shingles are not nailed directly to the sheathing in rain-screen applications, most codes still require plywood sheathing. Plywood sheathing transmits moisture better than OSB; therefore, if it gets wet, it dries more quickly.
You must request a variance to use OSB in a rain-screen application before installing the sheathing. Furring strips (nominal 1- by 2-inch dimension lumber (19 mm by 38 mm)) or nominal 2- by 2-inch dimensional lumber (38 mm by 38 mm) are placed over the building paper directly over each wall stud. The thickness of the furring strips or (2 by 2s) must be sufficient to avoid having the siding nails penetrate the felt or house wrap. Horizontal boards (usually nominal 1 by 4 inch dimensional lumber (19 mm by 89 mm)), spaced to coincide with the exposed shake or shingle length, are placed across the furring strips to give an open space between the backside of the shakes or shingle and the sheathing. The space is vented at the top and bottom and must be screened to keep out insects. The top may be vented directly into the soffit to connect the air-flow with the attic ventilation. Flashing must be installed around doors and windows just as with any siding system.