Many people think of sheathing as a base for nailing roofing shingles. However, when appropriately installed, it adds considerably to the structural integrity of the framing as it ties the trusses securely together. Consequently, it is extremely important to have professionals install the sheathing and select the proper material and fasteners. In coastal areas subject to hurricanes, sheathing loss is a common structural failure because of the extreme uplift of wind forces. It may be due to insufficient fastening, especially at roof corners, edges, and ridge lines.
What material should be used for sheathing to provide the best outcome? In a typical residential application, the options are exterior grade plywood or oriented strand board (OSB) in 4 x 8-foot panels. The thickness will range from 3/8 to 3/4 inches depending upon local code. If you refer to building codes, you will see wood structural panels encompassing both types.
Plywood is probably more familiar to homeowners in that it has been used in so many different applications. It is constructed from thin sheets (veneer) shaved from a log and then laminated using a hot press. The result is a solid structural panel that resists expansion and contraction but, like most woods, isn’t water friendly. That said, it offers the significant advantage that if it does get wet and swell, it will return to its nominal thickness as the wood dries. Generally, CDX plywood (the CD refers to the quality of the surfaces, and the X means exposure– it is rated for exterior use) is used extensively in sheathing applications. Plywood remains a popular choice for sheathing among builders who have used it for many years.
OSB consists of engineered panels made of compressed wood strands in perpendicular layers locked together by a phenolic resin adhesive. Compared to plywood, you won’t find any gaps or soft areas sometimes found in plywood. It has greater shear strength (i.e., resistance to layers sliding against one another) than plywood, although other factors are similar. If you need larger than standard panels, then OSB is the only option. It is generally less expensive than plywood and can be made from smaller trees, and is thus environmentally friendly. However, if it does get wet, there can be significant expansion along the edges, which will then show up in the shingles as they will curl.
As you can appreciate, sheathing is a very important step in completing a roof. It must be done correctly to resist high-force winds accompanying hurricanes and tornadoes. Let American Roofing evaluate your roofing or reroofing needs and install the best sheathing for your house. Get started today with a free estimate or certified roofing inspection, and you will see why we say American Roofing and Vinyl Siding, “we’ve got you covered”!