Architectural Specs for Western Red Cedar

In addition to Latin namedropping with Thuja Plicata, there are a number of other practices that are recommended to maintain proper specifications and instruct contractors on proper delivery, storage, assembly, and sequencing of construction using Western Red Cedar. To take advantage of these varied benefits and the many grades of knotty and clear Western Red Cedar, seasoned architects pay attention to the key specifications and detail notations recommended by producers and consultants. According to the WRCLA, there are 27 expert producers of Western Red Cedar lumber products, all in British Columbia, Washington, Oregon, and Idaho, who can provide project guidance and specification advice. In addition, there are specifier service programs and cedar application specialists in Seattle, Washington and the Minneapolis-St. Paul area of Minnesota.

Advice for specifiers tends to begin with type of application, drilling down to suitable wood grades, nominal sizes, proper moisture content, exposed surface and joint or connection details, such as fasteners.

Siding and trim. “It's best to use dry, acclimatized cedar, typically kiln-dried, for siding and trim,” says WRCLA's Paul Mackie. “Boards should be pre-stained or pre-primed on all six sides prior to installation.” For all siding types, Mackie suggests including a grading rule or grading agency paragraph citation with the specification—such as “NLGA 201a” or “WCLIB 106-a”—if the product is required to meet that specific written standard. The architect may also want to undertake a coverage calculation for project budgeting or as a construction administration (CA) phase takeoff. Assistance with coverage calculation variables, such as trim allowance percentages, is available in producer literature and from forestry industry groups.

Architects and other project designers should also note industry experts strongly recommend the use of high-quality, stainless steel fasteners for all exterior applications. “Western Red Cedar is primarily used outside,” says Mackie, “so fasteners have to be corrosion-resistant, such as stainless steel, which is the best choice.” He and other experienced wood-design professionals add that double-hot-dipped galvanized iron and steel work as an alternative, but the materials must meet the standard ASTM A153, Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware. Lesser classes of galvanized steel materials are likely to create streaking, but tensile-strength aluminum will also work well. “Iron fasteners can leave ugly black streaks on the wood, and the natural preservatives in the wood will damage copper,” adds Mackie, noting that stainless-steel fasteners should be specified as marine grade (316) for projects on or near sources of salt water.

For Western Red Cedar exterior siding, the aesthetic and design options are quite varied and worth careful consideration in the design development (DD) phase. “It's an extremely versatile product that offers many design choices for residential, commercial, and institutional structures, including single and multi-family homes, office buildings, retail, churches, band shells, hotels, and historic buildings,” says Lynne Christensen, MBA, CAE, director of operations with the Cedar Shake and Shingle Bureau. However, she cautions that they must be “specified and installed correctly.” Following is basic advice from the book, How to Specify Western Red Cedar:

▶ Layered bevel. Among the most widely specified cedar siding type, layered-bevel siding is a traditional look but can take on a contemporary feel in some settings.

Specifiers should indicate the nominal size, grade, moisture content (kiln-dried) and the surface to be exposed (smooth or resawn). Clear cedar is available in plain bevel, rabbetted bevel and wavy edge. Specification of knotty grades must include a choice of the type of bevel—again, plain, rabbetted, or wavy edge. Note also that some suppliers of Select Knotty grade will glue knots on the reverse face. The quantity of siding required is usually expressed in surface measure rather than number of members or the like.

▶ Tongue and groove. In addition to nominal size, grade, grading paragraph, moisture content, and exposed surface, the specifications for tongue-and-groove siding should indicate a product pattern.

Common patterns include EV2S, with a V-joint on two sides, as well as EV1S, with a V-joint on one side. The S2S flush joint pattern is also commonly selected, but there are many other patterns produced in addition to these three typical designs. The specifier must be sure of the desired look and the pattern that will achieve it. In the case of tongue-and-groove siding, quantity should be expressed in board feet.

▶ Lap siding. Channel siding, one type of lap siding, can be installed vertically, horizontally, and even diagonally.

The typical specs from the above siding types apply, but the specifier should note that lap siding is available unseasoned or seasoned (kiln-dried). As with tongue-and-groove, the quantity should be expressed in board feet.

▶ Board & batten. Designers can specify almost any desired size for this vertical siding type, though a typical composition is 1-inch-by-10-inch boards and 1-inch-by-3-inch battens. Quantities for these cladding systems should be expressed in linear feet or board feet. Boards are available in clear or knotty, green or seasoned, rough-sawn or surfaced on a side and two edges, with the latter called S1S2E.

▶ Trim boards. Expressing quantity in linear feet, the designer chooses from corner boards, fascia, skirting, and fenestration detail, and specifies a finish that is smooth on four sides (S4S), surfaced one side and two edges (S1S2E), or rough sawn on all sides (rough). As with siding, all specs such as nominal size, grade, grading rule paragraph, moisture content, etc., must be included.

Applying proper specifications to the project will help ensure that producer estimates and takeoffs are as close to the actual project needs as possible. It also helps to reduce delays in project construction and also callbacks due to poor craftsmanship. However like any other materials and systems, there are complications and questions, and a knowledgeable trade leader or representatives of the WRCLA will be able to offer model specification language and, in some cases, typical detail drawings.

Decking. Producers offer decking products in one of four agreed-upon decking grade categories: Architect Clear, Architect Knotty, Custom Clear, and Custom Knotty. This system for decking product grades is intended to simplify the process of specification regardless of preferred style and budget. Architects or contractors must include this grade spec along with size, moisture content and quantity (in linear feet). Specifiers should be aware that decking quantity must be determined in part by including spacing, typically 1/8-inch clear width, between planks and between the ends of boards.

Tables are available from engineers, carpentry subcontractors, the WRCLA and some producers to assist in calculations. The spacing is crucial for proper drainage and drying, as this will extend the like of the deck. Also, clients should be advised on proper maintenance. Debris and moisture collection can cause damage over time.

Timbers. Western Red Cedar timbers typically are left exposed to display their inherent beauty. Projects where they will be seen include commercial, institutional and residential projects in which timber strength and appearance are both deemed important, and also landscaping structures for parks, gardens and similar outdoor spaces.

Available in air-dried or unseasoned clear and knotty grades, timbers are rectangular beams-and-stringer elements or square post-and-timber structures. Timbers are specified Surfaced Four Sides (S4S), rough sawn, or rougher headed. Specs should include size, grade, grading paragraph, moisture content and quantity in linear feet.

Fencing. Specifications for fencing must include details for posts (vertical), rails (horizontal), and infill material to be attached to the rails, unless prefabricated fencing sections are to be used. Top boards are available in pointed, dog-eared, Gothic and spearhead patterns, among others. Lattice can be specified for a lighter, open appearance.

Fence and gate hardware should be rust and corrosion-resistant. Popular hardware options include 4-inch x 4-inch metal post supports set atop fins that are driven in-ground, which eliminate post-hole digging. Aluminum or galvanized metal brackets resembling joist hangers can be used to secure rails to posts and to simplify corner attachments. Pattern, size, grade and grading paragraph should be included in specs, with quantity expressed as number of posts/length in feet; for example, 24/8 feet. Moisture content is typically not called out when specifying fencing.

Specifying Siding for Sustainability

Knowing that Western Red Cedar is a renewable resource from sustainably managed forests, there is much to recommend the wood for use in the U.S. Green Building Council's LEED certification programs and others such as Living Buildings and Green Globes, among others. The environmental benefits are many but especially so in the Pacific Northwest and anywhere that Western Red Cedar can be locally sourced.

What some designers and specifiers may not know is that there is significant documentation available for Western Red Cedar siding. For example, life-cycle analyses (LCAs) have been commissioned to compare siding made of Western Red Cedar side by side with alternatives. The studies produced remarkable results: Western Red Cedar's life-cycle performance shown to have preferable environmental impact in five out of seven metrics when compared to brick, vinyl and fiber cement. “Western Red Cedar decking 'slew the dragon,' beating virgin vinyl and plastic composite in all seven metrics,” says Mackie. “And Western Red Cedar siding outperformed in five categories.” Because wood products have some emissions from finishing and refinishing processes, that was one area where it ranked behind other siding products. However architects active in wood design note that many low-emissions finishes are available that perform well.

The WRCLA has also issued one of the very few environmental product declarations (EPDs) for siding products. The EPD documentation covered the system 1/2-inch x 6-inch bevel siding. The group embraced this type of transparency early, producing two of the handful of peer-reviewed EPDs that have been available in recent years. “Determining the true cost of materials requires evaluating the overall costs of a product lifecycle,” said WRCLA's executive director Jack Draper of the study. “Our EPDs provide buyers of Western Red Cedar from member companies with accurate, verifiable environmental performance information.”⁵

 

C.C. Sullivan is a marketing consultant and content studio specializing in the architectural industries and AEC firms (www.ccsullivan.com).

 

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. RealCedar.com.