Direct answer: Above-ground cedar (decking, siding, railings) lasts 20-30 years. Fence posts in ground contact: 10-15 years. Raised garden beds: 7-12 years. These figures assume good installation with proper drainage and airflow. Western red cedar consistently outperforms eastern varieties.
Cedar Lifespan by Application
| Application | Exposure Level | Expected Lifespan |
|---|---|---|
| Above-ground decking | Moderate | 20-30 years |
| Cedar siding | Moderate | 25-30+ years |
| Cedar fence boards (above-ground) | Moderate | 20-25 years |
| Cedar fence posts (in-ground) | High | 10-15 years |
| Raised garden beds | Very high | 7-12 years |
| Cedar shingles (roof) | Variable | 20-30 years |
Why Cedar Resists Rot
Cedar's durability comes from naturally occurring organic compounds called thujaplicins -- potent antifungal agents that inhibit the growth of mold and decay-causing fungi. Cedar essentially treats itself from the inside out, requiring no chemical preservatives.
What Actually Affects Cedar's Lifespan
- Climate: In high-humidity regions, cedar loses its protective oils faster. Up to 40% of these oils can leach out within the first three years in wet environments.
- Ground contact: Nothing shortens cedar's lifespan faster. A post buried in wet clay might fail in 5-7 years.
- Airflow: Cedar that dries quickly after rain lasts dramatically longer. Use gaps between deck boards and spacers to keep cedar off concrete.
- UV exposure: Breaks down wood fibers. A UV-blocking stain prevents this.
How Long Does a Cedar Fence Last?
A well-maintained cedar fence typically lasts 15-25 years. The posts (in ground contact) are the limiting factor -- the boards themselves last longer. Set posts in gravel rather than direct soil contact to significantly extend their life.
- Cedar fence boards above-ground: 20-25 years with regular staining
- Cedar fence posts in gravel: 15-20 years
- Cedar fence posts in clay soil: 7-12 years
How Long Does Cedar Siding Last?
Cedar siding lasts 25-30+ years with proper maintenance -- one of the most durable natural siding materials available. Apply a UV-blocking exterior stain or oil every 2-3 years to maintain colour and replenish natural oils. Left untreated, cedar siding greys and develops surface checks but can remain functional for 15-20 years.
Heartwood vs Sapwood -- The Most Important Factor
- Heartwood (dark reddish-brown): dense inner core where protective oils are concentrated. This is where cedar's rot resistance lives.
- Sapwood (pale yellowish-white): outer layer lacking the protective oils. Decays at a similar rate to untreated pine.
When buying cedar for outdoor use: avoid boards with large pale sections. Specify "all-heart" or "select heart" grade for outdoor structural applications.
Sealing and Maintenance
Cedar does not need sealing to resist rot -- that is a common misconception. Sealing maintains the reddish-brown colour and replenishes oils lost to weathering. Oil-based penetrating sealers outperform water-based on cedar because they soak into the dense grain. Reapply every 2-3 years using the water bead test: if water soaks in rather than beading, reapply.
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