wood roofed house

Wood Roof Replacement

Wood shingles and wood shakes are manufactured from a variety of woods including Western Red Cedar, Alaskan Yellow Cedar, Eastern White Cedar, and Southern Pine. Wood roofing creates a uniquely natural, sometimes rustic look and is commonly found throughout the Northwestern United States. As a wood roof system ages the shingles and shakes weather to a lovely shade and give the supporting structure the appearance of blending naturally into surrounding landscapes. Wood roof systems tend towards a mid-range price point and can typically be installed for about $250 per square, or 10’x10′ area of roof space.

Wood shakes and wood shingles are not the same thing. In general wood shakes are thicker and rougher than wood shingles, which are cut to a uniform thickness and tend to have a smooth surface. Wood shakes are crafted by hand and involve splitting the log, whereas wood shingles are sawn on both sides. Quality wood shakes and shingles should be edge grain cut to prevent warping and splitting. They are typically manufactured from dead trees and salvage logs.

When considering a wood roof system it is advisable to consult a roofing contractor about local building codes. In certain areas the use of wood shingles and shakes are prohibited due to fire resistance concerns. Wood roof systems may have no fire rating or only a Class C fire rating. Certain wood roofing materials that have been treated with a factory-applied, fire-resistance treatment are available and provide the visual appeal of a wood roof system with a Class A fire rating.

How long a wood roof system lasts depends on a number of factors including proper installation and periodic maintenance. It is common for wood shingles and wood shakes to require occasional washing and re-oiling. The grade of wood used in a wood roof system as well as climatic issues such as proximity to salt-water and exposure to harsh elements also impact the durability and useful lifespan of wood roof systems.

Installation requirements for wood roof systems.

Roof Deck: According to the NRCA wood roof systems can be applied over closely spaced wood planks or continuous wood decking. For 16” rafter spacing’s plywood decking should be a minimum of 15/32 thick or ½ inch nominal exterior-grade. If oriented strand board (osb) is being used it should be a minimum 15/32 inch thick or ½ inch nominal exterior grade. For 24” rafter spacing’s 5/8 inch nominal thickness is recommended. In cases where an ice-dam protection membrane is required the use of solid roof decking or sheathing is advised. The NRCA recommends using caution when installing a new roof onto a roof deck made of OSB, preservative-treated wood, and wood treated with a fire-retardant coating. A qualified roofing contractor can provide information on appropriate roof decking materials for your roofing needs.

Underlayment: The underlayment provides temporary waterproofing during roof installation and acts as a permanent secondary waterproofing layer to the outermost roofing material. The NRCA recommendations for underlayment, commonly called “felt paper” specify a minimum of one layer of No. 15 or No. 30 asphalt-saturated, non-perforated felt applied in shingle fashion on roof decks having a slope of 18 degrees or more. The NRCA does not recommend the use of wood shakes and wood shingles on roofs with a slope less than 18 degrees. When wood shakes are being installed the felt paper used should be 18” wide and installed between courses of wood shakes. This is referred to as “interlayment.” For extremely cold climates the NRCA recommends one additional underlayment layer known as an ice-dam protection membrane. Your roofing contractor can provide information about the necessity of this type of weatherproofing.

Fasteners: Roofing nails used to install wood shingles and wood shake roofs should be made of galvanized steel, stainless steel or an equally corrosion-resistant material. The nails used to install wood roof systems should be long enough to fully penetrate all layers of roofing materials and reach into the underside of the roof deck. A least two fasteners should be used for each wood shake or shingle.

Flashing: When installing wood shake and wood shingle roof systems flashings should be installed around the perimeter edge, at any penetrations, in open valleys, and along vertical surfaces.

The NRCA doesn’t recommend any specific wood shake or wood shingle roofing products or manufacturers. Currently no American Society for Testing Materials (ASTM) standards exist for wood roof systems. A grading system for certain types of wood shakes and shingles does exist. The NRCA suggests the use of cedar shakes and cedar shingles with a No. 1 grade, as determined by the Cedar Shake and Shingle Bureau (CSSB) Standard CSSB-97. This requirement mandates the use of clear heartwood, no face defects, and a 100 percent edge grain. Carefully read wood shake and wood shingle packaging and product literature to determine quality and grade. A qualified roofing contractor can provide guidance and suggestions when selecting a wood roof system.

Wood roof systems come with warranties against manufacturing defects. These warranties typically cover failure specific to the wood roof product, and exclude issues arising from improper installation as well as climatic and environmental factors. It is very important to fully understand the provided warranty as well as to have clear knowledge of situations, such as improper installation and insufficient ventilation, which may void the warranty. Your roofing contractor should provide you with detailed warranty information pertaining to the specific wood roofing material you select, as well as warranties offered by the contractor to cover roof installation.