Fencing looks like one of the simpler outdoor projects. Two things routinely make it complicated: where the line actually is, and what happens to the posts.
Know the boundary
Assumptions about where a property line runs are frequently wrong, and an existing fence is not evidence — plenty of fences were built in the wrong place decades ago and have stayed there.
Building on a neighbour’s land is expensive to unwind, and it can create ongoing legal complications well beyond the cost of the fence.
For anything substantial, establish the boundary properly. A survey costs money and is considerably cheaper than the alternative.
Talk to your neighbour before building, particularly about a shared boundary. Fence disputes sour relationships for years, and most are preventable with a conversation.
Permits and local rules
Most Washington jurisdictions set a height below which a residential fence needs no permit, with taller fences requiring one. The specific height varies locally.
Beyond height, other constraints frequently apply. Corner lots usually have sight-line requirements limiting height near intersections, for road safety. Front yard fences are often held to lower limits than rear ones. Properties near shorelines, wetlands or steep slopes may fall in critical areas affecting what can be built.
Homeowners’ associations may impose their own requirements independent of the jurisdiction.
Check all of this before buying materials, not after.
Posts are the failure point
Fence panels rarely fail first. Posts do, and the mechanism differs across the state.
West of the Cascades: rot at ground level, where the post is in contact with persistently damp soil. Appropriate treated timber matters, as does how the post is set. Concrete that traps water around a post can accelerate rot rather than preventing it, so drainage at the base matters.
East of the Cascades: frost heave. Posts set above frost depth get lifted by freezing ground over successive winters, and a fence that has become uneven is usually telling you the footings are too shallow.
Footing depth requirements east of the Cascades are considerably greater than in the Puget Sound lowlands, and generic plans typically assume milder conditions.
Materials
Cedar. Traditional in Washington, naturally rot-resistant, weathers to grey unless maintained. Widely available regionally.
Treated timber. Less expensive, and appropriate treatment grade matters for ground contact.
Vinyl. No rot, no maintenance, higher upfront cost. Copes with damp well. Can become brittle in extreme cold, which is more relevant east of the Cascades.
Metal. Durable, and near saltwater — Kitsap, coastal Pierce, the Skagit islands — corrosion resistance matters.
Composite. Low maintenance, higher cost, performance varies by product.
Slopes
Washington has a lot of sloping ground. Fences on slopes are either stepped, with panels level and posts stepping down, or racked, following the slope continuously. They look quite different and not every product racks.
Worth deciding deliberately rather than discovering what your contractor assumed.
Getting it built
Verify registration, bond and insurance as with any contractor. Ask specifically about post setting method and depth, since that is what determines whether the fence is standing straight in ten years.
East of the Cascades, ask explicitly what frost depth they are setting to.