Western red cedar has earned a well-deserved reputation as one of the most versatile and durable building materials available for residential exteriors. Known for its natural resistance to decay, dimensional stability, and distinctive appearance, this softwood species has been a preferred choice for siding, decking, fencing, and exterior trim for generations. In a recent episode of the Fine Homebuilding PRO TALK podcast, Paul Mackie of the Western Red Cedar Lumber Association (affectionately known as Mr. Cedar) shared extensive insights into the properties, selection, installation, and finishing of this remarkable material. This article distills those expert recommendations into practical guidance for builders, contractors, and homeowners looking to make informed decisions about using western red cedar in their projects. Whether you are planning a new installation or maintaining an existing cedar exterior, understanding the material’s characteristics and best practices will help you achieve lasting results. For a detailed look at one popular application, see our guide on cedar shiplap siding installation and maintenance.
Understanding Western Red Cedar as a Building Material
Western red cedar (Thuja plicata) is native to the Pacific Northwest of North America, where it grows in coastal forests from Alaska down through British Columbia and into the northern United States. The tree’s natural growing environment, characterized by abundant rainfall and moderate temperatures, contributes to the wood’s unique cellular structure and performance characteristics. Unlike many other softwood species, western red cedar contains natural preservatives called thujaplicins that make it inherently resistant to fungal decay and insect attack. This natural durability is one of the primary reasons cedar has been used for exterior applications for centuries, with indigenous peoples of the Pacific Northwest utilizing it for everything from shelter to canoes to ceremonial objects.
Key Physical Properties
The physical properties of western red cedar make it exceptionally well suited to exterior use. Understanding these characteristics helps builders select the right grade and application for each project.
- Dimensional stability: Cedar has a low coefficient of thermal expansion and minimal shrinkage, which means it resists warping, cupping, and twisting better than many other wood species. This stability is especially valuable for siding and trim applications where maintaining a straight, flat surface is critical.
- Light weight: With a density of approximately 22 pounds per cubic foot at 12 percent moisture content, western red cedar is one of the lightest commercial softwoods. This reduces structural load requirements and makes handling and installation easier for crews.
- Thermal insulation: Cedar’s cellular structure contains millions of tiny air pockets, giving it excellent natural insulating properties. A cedar wall provides better thermal performance than many alternative cladding materials, contributing to overall building energy efficiency.
- Acoustic properties: The same cellular structure that provides thermal insulation also absorbs sound, making cedar an effective material for reducing exterior noise transmission.
- Workability: Cedar machines, cuts, and fastens with ease using standard woodworking tools. It accepts both paint and stain finishes exceptionally well when properly prepared.
Grades and Selection Criteria
Not all western red cedar is created equal. The Western Red Cedar Lumber Association classifies cedar into several grades based on appearance, knot size and frequency, and structural characteristics. Selecting the appropriate grade for your application ensures both performance and cost efficiency.
| Grade | Description | Best Application |
|---|---|---|
| Clear Heart | Highest grade, entirely free of knots and defects, consistent color, vertical grain | Premium siding, trim, millwork, high-visibility architectural features |
| Clear | Similar to Clear Heart but allows small sound knots and minor color variation | Standard siding, fascia boards, soffits, door and window trim |
| Select Knotty | Permits tight sound knots, wider color range, mixed grain patterns | Panel siding, fencing, rustic applications, decking |
| Utility Knotty | Larger knots, more color variation, some manufacturing imperfections allowed | Fencing, sub-decking, structural applications, economical sheathing |
When selecting cedar for exterior use, pay close attention to grain orientation. Vertical grain (quartersawn) material offers the greatest dimensional stability and resistance to cupping, making it the preferred choice for siding applications. Flat grain material is more economical but may exhibit greater movement with changes in humidity. For a broader overview of exterior cladding options, our article on beveled wood siding types and installation provides useful comparisons.
Installation Best Practices for Cedar Siding and Decking
Proper installation is critical to maximizing the service life of western red cedar exterior products. While cedar is naturally durable, poor installation practices can lead to premature failure, regardless of the material’s inherent qualities. The following guidelines reflect the best practices recommended by industry experts and the Western Red Cedar Lumber Association.
Siding Installation Fundamentals
Cedar siding requires attention to moisture management, fastening techniques, and proper detailing at transitions and penetrations.
- Acclimation: Allow cedar siding to acclimate to the job site conditions for at least 72 hours before installation. Store material off the ground in a dry, well-ventilated area, and protect it from direct sun and rain during the acclimation period.
- Moisture barrier: Always install a proper weather-resistant barrier behind cedar siding. A ventilated rainscreen assembly, which creates a minimum 3/8-inch air gap between the siding and the weather barrier, significantly improves drying potential and extends siding life.
- Fastening: Use corrosion-resistant fasteners, preferably hot-dipped galvanized or stainless steel nails. Electroplated galvanized nails can react with cedar’s natural extractives and cause black staining. Nails should be long enough to penetrate through the sheathing at least 1 inch into the framing.
- Nailing pattern: For bevel siding, nail above the overlap point so the fastener passes through only one board. For shiplap and tongue-and-groove profiles, blind nailing through the tongue hides fasteners and allows for wood movement. Our detailed guide on blind nailing techniques for cedar clapboard siding covers this method in depth.
- Clearance: Maintain minimum 2-inch clearance between cedar siding and grade, and 1-inch clearance below roof eaves. All horizontal surfaces, including window sills and trim tops, should have sufficient slope for water runoff.
- End grain sealing: Apply a quality end grain sealer to all field cuts, particularly on horizontal surfaces where moisture wicking into exposed end grain is most likely.
Decking Considerations
Cedar decking shares many installation principles with siding but presents unique challenges due to its horizontal orientation and exposure to foot traffic and standing water.
- Joist spacing: Space joists at 16 inches on center for 5/4-inch decking and 24 inches on center for 2-inch decking. Closer spacing reduces deflection and extends deck life.
- Fastener type: Use hidden fastening systems whenever possible to avoid exposed nail or screw heads that can trap moisture. When face fastening is necessary, use screws with corrosion-resistant coating and countersink slightly below the surface.
- Gap spacing: Leave a 1/8- to 1/4-inch gap between deck boards to allow for expansion during wet periods and to facilitate drainage and airflow.
- End joints: Stagger end joints across adjacent boards and ensure each joint bears fully on a joist or blocking. No cantilevered joints are permitted.
Finishing and Protecting Western Red Cedar
One of the most common questions among builders and homeowners is whether to paint or stain cedar. The answer depends on the desired appearance, maintenance commitment, and exposure conditions. Regardless of the finish chosen, proper surface preparation is essential for long-lasting results.
Paint versus Stain
Each finish option offers distinct advantages and trade-offs that should be carefully weighed before making a decision.
| Finish Type | Advantages | Disadvantages | Reapplication Cycle |
|---|---|---|---|
| Paint | Maximum UV protection, uniform color, longest service life between coats, hides grain variations | Opaque (hides natural wood appearance), requires more surface preparation, failure mode is peeling which is difficult to repair | 5-8 years |
| Solid stain | Good UV protection, uniform color, easier to recoat than paint, some wood texture visible | Opaque like paint, can still peel on horizontal surfaces, limited color retention on south-facing exposures | 3-5 years |
| Semi-transparent stain | Shows natural wood grain and color, easiest to maintain and recoat, breathable finish allows moisture vapor escape | Less UV protection, shorter service life, color fading inevitable, requires more frequent maintenance | 2-4 years |
| Clear sealer | Maximum natural appearance, preserves true cedar color initially | Minimal UV protection, shortest service life (6-12 months), wood will gray quickly if neglected | 1-2 years |
Surface Preparation and Application Tips
Regardless of the finish selected, following correct surface preparation and application procedures makes the difference between a finish that lasts and one that fails prematurely.
- Timing: Apply the first coat of finish as soon as possible after installation, ideally within two weeks. Cedar exposed to sun and rain for extended periods before finishing develops surface contaminants that inhibit adhesion. Pre-finishing siding and trim before installation, where practical, ensures all surfaces are protected, including back-prime caution areas.
- Moisture content: Ensure cedar moisture content is below 15 percent before applying finish. Use a moisture meter to verify, especially on material that has been on site for some time. Finishing wet wood traps moisture and leads to premature finish failure.
- Back priming: Always back-prime cedar siding and trim before installation. This simple step prevents moisture wicking into the wood from behind, reduces cupping, and significantly extends the life of the finished installation.
- Application method: Brush application provides the best penetration and adhesion for stains and paints. Back brushing after spray application ensures the finish is worked into the wood surface and eliminates pooling and drips. Two thin coats outperform one thick coat in both appearance and durability.
- Weather windows: Apply finishes when temperatures are between 50 and 90 degrees Fahrenheit, and when rain is not expected for at least 24 hours. Avoid finishing in direct sun, which causes the finish to dry too quickly and reduces penetration.
Addressing Common Cedar Performance Issues
Even with careful material selection and proper installation, cedar exterior products can develop performance issues over time. Understanding the causes of common problems helps builders diagnose issues early and implement corrective measures before significant damage occurs.
Moisture-Related Problems
Moisture is the most common cause of premature failure in cedar exterior applications. While cedar is naturally decay resistant, no wood species can withstand continuous exposure to trapped moisture.
Cupping occurs when the bottom edge of a siding board absorbs more moisture than the top edge, causing the board to curl. This is typically caused by inadequate back priming, insufficient clearance above roof surfaces, or splashback from the ground. Proper flashing at all horizontal transitions and maintaining recommended clearances are the primary preventive measures. For a deeper look at this issue and strategies to prevent it, read our article on vertical cedar siding cupping causes and prevention.
Black staining on cedar surfaces can result from several sources. Tannin bleed appears as dark streaks when water extracts natural compounds from the wood and deposits them on the surface. This is typically a cosmetic issue that diminishes over time as the wood weathers. Mildew and mold growth indicate persistent moisture conditions and poor air circulation. Power washing with a mild bleach solution followed by rinsing usually restores the surface, but addressing the underlying moisture problem is essential for a permanent solution.
Checking and splitting in cedar siding is often caused by rapid drying after a wet period, or by fasteners placed too close to board edges. Using proper nailing patterns and maintaining adequate gap spacing helps minimize these issues. Small checks are primarily cosmetic and do not affect structural performance, but large splits that extend through the board thickness should be replaced.
Natural Weathering and Graying
Unfinished western red cedar exposed to the elements will naturally weather to a silvery gray patina over time. This process is not a sign of decay or deterioration. The gray color results from the breakdown of lignin in the wood surface by UV radiation, combined with the leaching of natural extractives by rainfall. The weathered layer is only a few thousandths of an inch thick and protects the underlying wood. Many homeowners deliberately leave cedar unfinished to achieve this natural weathered appearance, which can persist for decades with no maintenance beyond occasional cleaning.
If the natural gray look is desired, no finish application is needed. However, if the goal is to retain the original warm amber color of freshly milled cedar, a UV-inhibiting clear sealer or semi-transparent stain must be applied and maintained diligently. Once cedar has grayed, returning it to its original color requires sanding or chemical stripping, which is labor-intensive and not always successful.
Western red cedar remains a premier choice for residential exterior applications when selected, installed, and finished according to best practices. Its natural beauty, durability, and workability make it a material that performs well across diverse climates and design styles. By understanding the properties of different grades, following proper installation techniques, and committing to an appropriate maintenance schedule, builders and homeowners can expect decades of service from their cedar exteriors. The investment in quality material and careful workmanship pays dividends in long-term performance and enduring curb appeal.