Roof Sheathing Basics
The skeleton of a roof is formed with rafters or trusses, generally spaced 16 inches or 24 inches apart from the center of one rafter to the center of the next. To stabilize the rafters, support the roofing material, and hold the entire roof together, roof sheathing is installed. Common roof sheathing materials include several types, which are chosen depending on the budget and weather conditions of the area.
Unless you're an experienced contractor yourself, the term “roof sheathing” is probably completely foreign to you. All the more reason to hire a pro to handle the repair or replacement of your roof's framework.
If you're in search of quotes for a roof sheathing job, ImproveNet can put you in touch with up to four local contractors for free! And if you're still wondering what roof sheathing is and what materials are typically used, read on and satisfy your curiosity.
Roof Sheathing Materials
Comes in standard 4-by-8-foot sheets, is strong, durable, and relatively light. It also holds roofing nails well. The common grade of plywood for roof sheathing is CDX. As a quick primer in plywood, each side is rated from A to D. A is smooth and knot-free while D, the lowest quality, has missing knots and cracks. One side is usually better quality than the other—C in this case. It should be placed up on the roof. X stands for exterior use. For rafters spaced 16 inches on center, ½-inch plywood is standard. For rafters spaced 24 inches on center, 5/8-inch plywood is preferred to minimize sagging.
Oriented strand board (OSB)
Made up of multiple layers of wood strands compressed at odd angles to each other and bound with water-resistant adhesives. It comes in 4-by-8-foot panels, as does plywood, and is commonly used interchangeably with plywood, such as for roof decking. It is a little cheaper than plywood, which is why it is popular on housing tracts as a cost-saving measure. But many roofers believe that it is not as strong as plywood and in particular does not have equal nail-holding power. If using OSB, note that one side has a slip-resistant coating that should be placed facing up.
Tongue and Groove
Commonly used as roof sheathing where a ceiling will not be installed and they will be visible from inside the house, such as across beams in a vaulted ceiling. Wood is an excellent insulator and in moderate climates no additional rigid insulation on the roof is necessary. The boards can be painted, stained, or coated with polyurethane to retain their natural color.
Commonly used for shingle, shake, or tile roofs. The boards were normally either 1-by-6 or 2-by-6. The spacing was to permit air to circulate under the shakes and shingles, particularly shingles. Tiles were designed so that lugs, or short protrusions, on the top backside of each tile would hook over the step sheathing. More recently, however, most roofers recommend solid sheathing on the roof to give the house additional resistance to movement, or shear strength. Step sheathing can then be applied over the solid sheathing as needed. Shingles, which must permit air to circulate under them, are now often placed on a special membrane that permits circulation.
1-by-8 boards, commonly used on the eave and rake overhangs when soffits will not be installed rather than as roof sheathing. The boards are more attractive when viewed from underneath than rough plywood. The ¾-inch thick boards extend from the eaves just past the exterior walls, where they butt up against the plywood roof sheathing. Roof material then covers all.
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