How Long Does a Cedar Fence Last in Seattle?
A well-built cedar fence in the Seattle area commonly lasts 15 to 20 years. Some go longer; plenty fail sooner. The difference is rarely the boards — it is the posts, what they are set in, and how long the bottom of the fence stays wet each winter.
Here is why cedar behaves the way it does in a wet climate, where it fails first, and the choices that add years.
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What the Research Says About Cedar
The USDA Forest Products Laboratory’s Wood Handbook groups woods by how well their heartwood resists decay. Western redcedar heartwood is in the resistant group — not the “very resistant” group. The handbook explains what that means in practice:
“…heartwood of a species in the resistant category generally gives satisfactory service for wood used aboveground, whereas those in the very resistant category generally give satisfactory performance in contact with the ground.”
Three more points from the same chapter matter for fences:
- Sapwood is not durable. “Untreated sapwood of essentially all species has low resistance to decay.” Cedar boards with pale sapwood edges decay faster at those edges.
- Second-growth wood is less durable. Wood from old-growth trees is often more decay resistant than wood from younger, second-growth trees — and most cedar sold today is second growth.
- Ground contact changes everything. Decay resistance may be lower for wood in contact with the ground, and for severe decay conditions the handbook generally recommends pressure-treated wood rather than naturally resistant heartwood.
That is the whole story of a cedar fence in one paragraph: cedar boards above the ground do well; cedar posts in wet soil are the weak point.
Where Cedar Fences Fail First
Posts at ground level
The few inches just above and below the soil stay wet and oxygenated — ideal for decay. A post can look fine above ground and snap there in the first big windstorm.
Board bottoms and rails
Boards touching soil, mulch or a planting bed wick water up. Bottom rails catch water on their top edge and rot from the fasteners out.
Gates
The heaviest, most-used section. Hinge posts loosen, frames rack, and a gate that drags stays wet at the bottom.
Why Seattle Is Hard on Wood Fences
Long wet season
From fall to spring, fences rarely dry out completely, especially on shaded north sides and under trees.
Soil that holds water
Clay and the dense glacial till found across much of the region drain slowly, so water sits around posts instead of draining away.
Moss and shade
Moss and mildew hold moisture against the wood. Fences behind hedges or under conifers age fastest.
How to Get More Years From a Cedar Fence
Better posts
Steel posts behind a cedar face, or ground-contact pressure-treated posts, instead of cedar posts in the ground. This one change addresses the most common failure.
Post setting that drains
Gravel at the bottom of the hole and concrete crowned above grade so water runs away from the post rather than pooling against it.
Boards off the ground
A gap of an inch or two between the bottom of the boards and the soil, or a replaceable kick board at the bottom.
A cap on top
A top cap and post caps keep rain off end grain, where wood absorbs water fastest.
Stain and cleaning
A penetrating stain every three to five years, and washing off moss. See fence staining and sealing.
Room to dry
Cut plants back from the fence and keep beds, mulch and soil from piling against it.
Repair, Replace or Switch Materials?
Under about ten years
A few failed posts or a storm-damaged section are usually worth repairing. See fence repair.
Past 15 years
If many posts are soft at the base and boards are cupped along whole runs, replacement usually costs less than repeated repairs. The repair vs replacement guide walks through it.
Tired of staining?
Composite, vinyl and aluminum do not decay. Compare them in the materials-for-Seattle-weather guide.
Frequently Asked Questions
Do cedar fence posts last as long as the boards?
Usually not. Posts in the ground are the part cedar is least suited to, which is why steel or ground-contact treated posts are common under cedar fences.
Does an unstained cedar fence last as long?
The boards still resist decay, but they gray, check and cup faster, and moss takes hold more easily. Stain mainly protects appearance and slows weathering; it does not fix wet posts.
Is pressure-treated pine better than cedar?
For posts in the ground, ground-contact treated lumber is generally more durable. For boards, cedar stays straighter and looks better. Many fences use both.
Sources
- Wood Handbook: Wood as an Engineering Material (FPL-GTR-282), Chapter 14: Biodeterioration of Wood USDA Forest Service, Forest Products Laboratory, 2021 Table 14-1, heartwood decay resistance groups; notes on sapwood, second growth and ground contact.
- Wood Handbook — publication record USDA Forest Service
Links and figures last checked against these sources: . Codes change — confirm the current rule with the city before you build.