RESIDENTIAL WOODEN SHAKES and SHINGLES

The most important wood property to consider when buying shingles is durability, its resistance to decay. Some woods, such as western red cedar, have natural durability. The heartwood of old-growth western red cedar is rated as extremely durable because of its extractives. However, the generally small amount of sapwood associated with this species is not durable. The consensus is that some second-growth timber, even from a decay-resistant species, is not as durable as the old-growth timber. Nevertheless, the durability of any wood decreases as rain or other sources of moisture leach extractives from the wood. For these reasons, the use of a “durable and treated” wood for shingles is increasing.

The most commonly used wood for shingles is western red cedar. Treated southern yellow pine taper-sawn shingles are also available. If the shingles are properly treated, other species can also be used. Using preservative-treated or naturally durable wood for shingles should result in a roof free of decay for 25 to 30 years. Weathering is erosion from sun, wind, debris, and precipitation. Even wood that does not decay is still subject to weathering. The weathering process removes about 1/4 inch of unprotected wood per century for soft woods (like cedar) on vertical exposures, but more wood is removed from roofs. Shingles are often left to weather naturally and, depending on exposure and climatic conditions, the wood will turn silver, dark gray, or dark brown. Applying finishes, especially those with pigment, can reduce weathering. Some preservatives retard decay and finishes retard weathering.

Proper selection of materials will appreciably influence the service life of wood shingles. Use only the top grade of shingles manufactured with edge-grained heartwood (or treated sapwood). A lower grade of shingles can be used on sidewalls or areas that require an undercourse. Roofs, unlike walls, have the most direct and extreme exposure to rain and sunlight.