Wood Shingle Basics
Recently the terms “shingle” and “shake” have been used interchangeably, but the two are different. The thin, tapering slats of wood used for roofing were historically called shingles, whether they were hand split or machine cut. The term “shake” is a more recent development, used to distinguish between split-wood (shakes) and machine-sawn (shingles). Wood shingle roofs can last as long as 30 to 60 years, provided the shingles are of good quality (i.e., vertical grain) and are installed so that they provide adequate coverage with the recommended amount of overlap beween courses.
The most important aspect of installing a wood roof is to allow for proper air circulation. Traditionally, wood shingle roofs were supported by frameworks that allowed the shingles to breathe underneath through the attic space (from which they were visible) as well as on the exterior surface.
The most common systems used skip sheathing (1x4 or 1x6 boards, spaced with the courses). The gaps in the substrate allowed the shingles to dry out from both sides, making this method ideal for roof longevity, especially in warm, high-moisture climates.
Skip sheathing usually isn’t practical for homes in colder climates, or those with finished or insulated attics, however. An alternative method is closed decking. A close deck is formed by installing solid plywood to the roof, then applying 1x4 battens (also called nailers or sleepers) at regular intervals. The shingles are nailed to the battens, allowing air to circulate underneath and preventing any moisture build up. It also permits the use of a breathable underlayment applied over the solid decking—roofing felt, house wrap, or breathable mesh.
While nailing wood shingles directly to solid decking is still permitted by code in some areas, the lack of ventilation can reduce the life of shingles significantly, in some cases to less than five years. That said, most of the shingles in an 1980s installation at Beauport, right on the ocean in cold, windswept Gloucester, Massachusetts, survived in reasonably good shape for nearly 30 years, according to the site’s blog (historicnewengland.org).
Another wood shingle issue is the type of felt used. The most common felts are 15# (15-pound) and 30# (30-pound) asphalt, which are paper based and semipermeable. In recent years, the roofing market has gravitated toward synthetic felts, which are not permeable. The synthetic felts can be left in the open much longer than the paper-based felts, and don’t wrinkle when rained on, so they’re more forgiving under asphalt shingles.
Under wood roofing, however, synthetic underlayments can cause problems, especially in combination with insufficient ventilation of the roofing material. According to the Cedar Shake & Shingle Bureau (cedarbureau.org), heat buildup cannot pass through a nonpermeable underlayment, causing the shingles to “cook” from the underside up, shortening the life of the shingles.
It’s also important to plan ahead for any variations in pitch change or unusual architectural features. Some common roofing practices, such as skimpy coverage or using staples as fasteners rather than hot-dipped (zinc-coated), aluminum, or stainless-steel nails, should be avoided. Use the best quality wood shingles you can afford with a surface texture similar to the old roof, or order custom shingles that accurately replicate the appearance of the original shingles.