Lessons Learned

In fact, western red cedar is one of the few wood species that are naturally at home in the outdoors, making them ideal for these kinds of structural and decorative exterior applications. “Properly finished, western red cedar will last for decades, even in harsh environments. Its natural resistance to moisture, decay and insect damage make it the ideal choice for a surface that is exposed to sun, rain, heat and cold all year round,” according to a WRCLA guide.

A range of western red cedar products that goes well beyond those specified for the Sandy High School project are now on the market, providing for a variety of potential applications. Western red cedar timbers may have clear or knotty grades with smooth surfaced, combed or rough sawn finishes; kiln dried or unseasoned (green); flat grain and vertical grain. Products and applications include:

• Siding & trim, with precut and seasoned panels and trimboards, includingbevel, tongue & groove, lap and board-and-batten type claddings.

• Structural decking, outdoor decking, fencing, pergola kits, and other outdoor lumber systems.

• Indoor materials, including grades for cedar paneling and moldings.

• Timbers of various grades, sizes and fasteners for western red cedar timbers.

For nominal widths, thicknesses and grades of some commonly available western red cedar lumber products, specialized suppliers and the WRCLA provide information and technical data. Western red cedar produced by some of the suppliers includes specialty end-use grades as well as products graded to National Lumber Grading Authority (NLGA) rules. NLGA grades are approved by the American Lumber Standards Board of Review and are accepted under all U.S. building codes.

Clear western red cedar (clear grades) have a limited number of natural characteristics and is specified when high-quality appearance is desired. These timbers are normally supplied green, or unseasoned, and may be seasoned using air-drying, as needed. Knotty grades present a more rustic appearance and are typically supplied green in the appearance and structural grades. When required, seasoning is achieved by air-drying except for grades used for light framing and for structural joists and planks, which are available kiln-dried.

Surface textures employed for architectural effect include saw textured, which is obtained during the milling process using either a circular or band saw. The effect appears on the face of the lumber. Rougher headed is the description of lumber that receives its rough texture from a milling process in which roughened planer knives are used; again, it is seen on the face. Often these products are furnished S1S2E- (Surfaced 1 side, 2 edges), with a saw textured rougher head face. Often these products are reversible. Last, the designation surfaced four sides, also known as S4S, presents a smooth appearance on four sides and a very uniformly sized product with a high quality appearance. These architectural-quality surfaced textures are available in siding and trim in 1”, 5/4” and 2” thicknesses and in timbers 4” thick and larger. Larger sizes are readily available, but may need to be special ordered.

Fasteners used with western red cedar include wide-diameter hardware of hot-dipped galvanized, aluminum, and stainless steel, which are all corrosion resistant. Other types of nails are not recommended, says WRCLA's Mackie, due to poor performance from rusting and adverse reactions to the otherwise beneficial natural fungicide, thujaplicin, which provides the wood's inherent strength and high resistance to decay and rotting. The chemical reactions may also lead to staining and streaking that is visible to building occupants or visitors. (This includes copper nails.) No. 304 stainless-steel fasteners tend to work very well for general applications, especially if the wood is to be finished with transparent or semi-transparent stain; for coastal and corrosive environment, No. 316 stainless steel is effective.

For heavy-timber construction as used at Sandy High School, typical connectors used include carriage bolts, lag screws, split rings and shear plates, and custom made hardware assemblies. Mechanically fastened joints must consider dimensions for end spacing and edge spacing, as well as product moisture content. WRCLA notes that fabrication and installation costs make up the lion's share of the budget for a heavy timber structure, so it is important to engineer the details of the structure before designing the timber members.

A last but important consideration is finish choice and application. Opaque finishes such as paint provide a high degree of surface protection for any lumber against weathering and wetting. However it does conceal some of the wood's characteristics. Natural finishes are highly desirable and generally require some level of regular maintenance to optimize the product's appearance and life-cycle performance. Transparent stains that modify the color or tone of the wood, for example, are available in waterborne and solvent-borne formulations, but unpigmented or lightly pigmented finishes provide limited protection against the sun's ultraviolet light and moisture related damage. Frequent refinishing is recommended, and it is an easy process for transparent stains, demanding only minimal surface preparation.

According to WRCLA, solvent-borne, oil-based semitransparent penetrating stains are ideal for western red cedar. These formulations penetrate the wood surface and are porous, so they lack the surface film created for example by paints. These stains perform best on western red cedar with a textured surface; in all cases they protect the cedar surface from damaging UV effects. A typical service life on siding applications may vary from three to six years depending on the western red cedar surface texture, quantity of stain applied, and the intensity of the sunlight on the wood surface.

In addition, latex semitransparent stains may appear similar to solvent-borne stains, but the latex product tends to be a thin film with little penetration into the wood. It may not be thick enough to provide the same durability as solvent-borne stains and has been known to degrade by flaking from the wood's surface. Much more substantial surface preparation is required for refinishing when using the latex products. “However, as increasingly restrictive environmental standards reduce the availability of solvent borne stains, ongoing research suggests that penetrating, erodible latex semi-transparent stain finishes for western red cedar will be available in the near future,” according to the Western Red Cedar Lumber Association.

In general, any rules applicable to good wood finishing will apply to western red cedar. Plan for regular maintenance of outdoor wood finishes. Specify proper surface preparation so that the contractors achieve a durable, long-lasting exterior finish. Application of finishes is likely to be just as important as the finish-substrate combination chosen for the red cedar surfaces. In fact, many factors influence finish performance and life-cycle, including the unique properties of western red cedar and manufacturing characteristics and construction practices used for each building project.

These factors are increasingly important for commercial and institutional buildings using western red cedar as part of their designs. With the varied products available and by using inventive combinations, architects like DOWA-IBI, Ankrom Moisan Architects, Inc. (which designed AVA Ballard near Seattle), and California's SEMA 4 see the use of western red cedar as an integral part of their design expression. It can also be the secret to good life-cycle performance—as well as a way to improve a nonresidential building projects' sustainability.

C.C. Sullivan is a marketing communications consultant specializing in architecture and construction.

 

Endnotes
1.	http://www.engineeringtoolbox.com/wood-density-d_40.html
2.	McGraw-Hill Science & Technology Dictionary (McGraw-Hill Dictionary of Scientific and Technical Terms)
3.	City of Sandy website, http://www.ci.sandy.or.us/index.asp?Type=B_ BASIC&SEC={1D15D680-C1F5-42DE-A882-59ABB3EC8B11}
4.	“Walk in the Woods,” Architectural Record, January 2013
5.	http://www.awc.org/pdf/wcd5.pdf

 

The Western Red Cedar Lumber Association is a Vancouver-based non-profit association representing 17 quality suppliers of Western Red Cedar lumber products in Washington, Oregon, and British Columbia (Canada). Founded in 1954 and known as “the voice of the cedar industry,” the WRCLA delivers market programs throughout the United States and Canada to support its members’ cedar products with information, education, and quality standards. www.realcedar.com