The post looks fine above ground and the concrete is solid — but the wood in between has turned to mush. Here's why that spot fails first.
"Five-year-old fence, posts rotted out — is that normal?" is one of the questions fence builders see most often online, and Florida homeowners ask it a lot. The failure nearly always looks the same: the post snaps or leans right at ground level, and when it's pulled, the rot is concentrated in a band just above or just inside the top of the concrete. The rest of the post can look almost new.
Wood decay needs moisture, oxygen and fungus at the same time. Deep underground there's water but little oxygen. Above ground there's oxygen but the wood dries out between rains. The band at grade gets all three, all the time — and in Tallahassee's heat, humidity and heavy summer rain, it rarely gets a chance to dry.
Concrete can make it worse. When the top of a footing is poured flat or dished below grade, it forms a small cup around the post. Rain and sprinkler water run down the post and sit there. Wood also shrinks slightly as it dries, opening a gap between the post and the concrete that holds water like a sponge. Experienced builders repeatedly point to this: it isn't concrete itself that rots posts, it's water trapped against the wood with nowhere to go.
Several everyday things keep the grade line wet:
Treated lumber is rated for how it's meant to be used, and wood intended for ground contact is treated differently from wood intended only for above-ground use. A post that isn't rated for ground contact will fail much faster when it's buried. When comparing quotes, it's worth asking what rating the posts carry — and it's one reason post material matters as much as picket material, as covered in our cedar vs. pressure-treated pine comparison.
If one or two posts are gone, the usual fixes are to dig out the old footing and set a new post, or to install a repair bracket or steel post beside the old one. If rot is showing on many posts at once, it's worth stepping back and applying the repair vs. replace 20% rule before paying for piecemeal fixes. Either way, if the new posts go in the same way the old ones did, expect the same result.
Push firmly on each post near the top. Any post that moves when its neighbours don't, or any soft spot you can press a screwdriver into at the base, is a post that won't survive the next tropical storm. Catching it now is much cheaper than replacing a whole section after it's down.
Call for a free consultation and we'll check the fence line with you, or see our wood fence installation page.