One corner is low. Or the railing has stopped looking true, or there is a gap where the deck meets the house that was not there last year. The first thing most people think is that the foundation has started to go.
Usually it hasn't. Deck post settling is its own problem. Your deck isn't standing on your foundation; it has its own set of small footings, and they move on their own schedule.
Deck posts settle because each one stands on its own small footing, poured shallow and often set in ground that got moved when the house was built. When water takes the soil out from under one, that post rides down by itself, which is why a deck can go well out of level while the house never budges.
Your deck stands on its own little foundations
A house sits on a continuous footing that runs all the way around it, poured below grade, tied together, carrying a lot of weight over a lot of surface.
A deck gets none of that. Under each post there is a separate pad, usually a couple of feet across at most, poured on its own and connected to nothing. Six posts means six independent foundations, each one trusting whatever dirt happened to be under it on the day it was poured.
That independence is the whole story. A house has to move as a unit, so it resists. A deck does not. One pad loses its bearing and that one corner comes down while the other five stay where they are, which is exactly what produces the twist you are looking at.
They were poured shallow
Deck footings sit close to the surface, in the layer of ground that takes on water, dries out, washes and shifts. A house footing is below most of that action. A deck footing is right in it.
They carry almost nothing
This sounds like good news and it isn't. A deck is light. The owner's crews run into the consequence from the other direction, on the rare job where they set a base for a deck that has not been built yet: they have to drive the steel down mechanically because, as he puts it, "there's no weight there to press it down, so you gotta get it down somehow."
Weight is what seats a footing into firm bearing. A house presses its own footings down until they find something that pushes back. A deck never weighs enough to do that, so it just rests on whatever it was set on and takes that ground's word for it.
The ground behind your house is the most disturbed ground on the lot
Decks go on the back. The back of a metro Atlanta house is also where the excavation happened, where the basement or crawl space wall got backfilled, and usually where the lot falls away.
Backfill is not undisturbed ground. It is the dirt that came out of the hole, pushed back in around the wall, packed at the top if it was packed at all. Builders drop rock and rubble in there too. It looks like a yard, it grows grass, and it keeps settling quietly for decades. A deck built off the back of the house frequently has at least one post standing on it.
Then add water. Gutters discharge at the back corners. Patios and walkways shed toward the low side. A grade that falls back toward the house pools water exactly where those pads are. A few of the downpours we get here will wash a hollow under a shallow footing without leaving any sign on the surface.
And no, it isn't the clay
You will read everywhere that Georgia red clay swells when it rains and shrinks when it dries, and that this is what heaves your footings around. The USDA soil survey rates the clay under most of metro Atlanta low for shrinking and swelling. It is dense, not expansive.
What moves a footing here is water, slope, fill and erosion. That matters to you because those four have fixes, and a soil type does not.
What does settling actually mean under a post?
There are two different things that look identical from the yard, and only one of them is settling.
The owner draws the line himself, describing a back deck: "The post itself is not rusting, it's not bowing, it's settling because the dirt is dropping, and it's all dropping underneath it."
That is the distinction worth carrying into the conversation. A post that has rotted at the base or rusted through has failed, and the ground under it may be perfectly fine. A post that is still sound but sitting two inches lower than it used to has not failed at all. The dirt left. Which one you have decides what happens next, and the deck post repair page sorts the symptoms out in detail.
Use the house as your level, not a bubble
Here is the useful trick, and it works from the deck without any tools.
Every deck is built with a deliberate slope away from the house so rain runs off, which means a bubble level lying on the boards tells you very little. The house is the fixed thing. Measure everything against it.
The line where the deck meets the house
That connection is the reference. Sight along it. If the deck has dropped away from the house anywhere along that line, or a gap has opened that you can get a finger into, that is the reading that matters most and the one worth acting on soonest.
The railing and the roof edge
Stand at one end and sight down the top rail. It was installed straight. Any dip or wave in it now is the deck telling you which post went down. On a covered deck, do the same along the roof edge above the posts, which is often easier to read than the rail.
Which way the boards run downhill
Decks slope away from the house on purpose. They are not supposed to slope sideways. If a ball rolls along the deck rather than off the front of it, a post on that side is low.
A settling deck is a safety question in a way a settling porch is not
This deserves saying plainly.
A porch at ground level that has dropped an inch is an appearance problem and a water problem. A deck is different in two ways: it is elevated, and it is holding people up. The load runs from the boards into the beams, into the posts, and down through those small footings, and that path was designed with the posts plumb and bearing evenly.
When one post drops, its share of the load does not disappear. It shifts onto the connections and framing that did not move, and onto the point where the deck attaches to the house. That is more strain than those parts were drawn for.
None of which means it is coming down this afternoon. A deck that has settled an inch and is otherwise sound is not an emergency, and nobody should be telling you it is. It is a reason to get it looked at this season rather than watching it for another two years, and a reason not to host thirty people on it in the meantime.
Why jacking it up and shimming the gap doesn't hold
This is the first idea most people have, and it is worth understanding why it disappoints.
The owner's version of the shortcut, from a settled porch: "If it went down 3 inches, and you find you some 3-inch wood, crib it up and fill that gap." It closes the distance. The deck reads level again. He is equally direct about how long that lasts: "it ain't gonna hold."
Nothing about that changes the ground. The same washed-out soil is still under the same shallow pad, and it is still going. In a year or two the shim is doing nothing and the corner is low again.
Anglin's will still do it if that is genuinely what you want, and they will tell you up front there is no warranty behind it. Some people are selling in the spring and that is a fair trade to make with their eyes open.
The repair that does hold works below the problem instead of above it. A steel pier goes down beside the failed footing until it reaches ground that can carry the load, and the lift comes off that. In the owner's phrase, you have to "get below that vulnerable soil" first. The method, the pier count and what it costs are all on the service page.
Two pilings, an inch and a half, and a sagging roof
What settling looks like by the time somebody picks up the phone, in a customer's own words:
"My home is on a concrete poured wall basement foundation. The front deck and roof above rests on two pilings that had settled about 1.5-2.0 inches resulting in the deck and roof above sagging. I called Anglin's and got an estimate to repair and agreed to the work. The workers showed up on time and did the job quickly and professionally. They were polite and respectful and cleaned up after themselves."
Eric Watkiss, 5 stars
Two supports out of however many that deck had. An inch and a half. The house itself, on a poured basement wall, was not part of the problem at all.
Four things to look at before anybody comes out
None of these cost anything and all of them make the visit shorter.
- Sight the top rail and the roof edge from one end and note where the dip is. That points at the post.
- Check where the deck meets the house for a gap or a drop along that line.
- Walk out after a hard rain and look at where water stands near the posts, and where your downspouts are actually letting go.
- Look at the base of each post for soil that has pulled away from the concrete, or a pad sitting proud of the ground around it.
If the low corner lines up with the wet corner, you have already done most of the diagnosis.
Frequently asked questions about deck post settling
Is a deck that has settled still safe to stand on?
A deck that has dropped an inch or so and is otherwise sound is generally fine for normal use, and it is not going to let go without warning. What has changed is the margin, because load that a settled post used to carry now leans on the connections around it and on the attachment to the house. Get it looked at this season rather than next year, and go easy on large gatherings until it is back where it belongs.
How much deck movement is normal?
Some is. Wood shrinks, swells and cups with the seasons, boards cup and gaps open and close, and no deck is perfectly flat after a decade outdoors. What is not normal is a permanent change in shape: a rail that has developed a dip, a corner that stays low through wet and dry weather, or a gap at the house that keeps getting wider.
Does a sinking deck mean my house foundation is moving too?
Often not. Deck footings are shallow, separate and lightly loaded, so they can give up ground the house never notices, and plenty of settled decks stand next to foundations in perfect condition. It is worth a look at the house anyway while somebody is on the property, because the water that undercut a deck pad is sometimes running against the house as well.
My deck feels bouncy underfoot. Is that settling?
Usually it is something else. Bounce and sway come from how the deck was framed, how far the joists span and whether it was braced, and none of that involves the ground. A deck can be springy with perfect footings, and it can be rock solid while a post quietly sinks. Framing and bracing belong to a deck builder rather than a foundation crew.
The deck stood fine for fifteen years. Why is it moving now?
Something changed about the water, most of the time. A gutter came loose or a downspout got redirected, a neighbor regraded, a tree that was drinking a lot of groundwater came down, a patio was added that now sheds toward the deck. Erosion also works slowly, so the soil under a pad can thin out for years before the footing finally loses enough support to drop.
Can I stop the ground under my deck from washing out?
Often you can slow it down a great deal. Get the downspouts nearest the deck discharging well away from it rather than at the corner, keep the gutters clear so they are not overflowing at the fascia, and fix any spot where the grade sends water back toward the posts instead of away. That is ordinary yard drainage, it is cheap, and it protects the repair once the footings are back down on solid ground.
See what the ground under your deck is doing
Somebody can stand at the low corner, sight the rail, look at where the water goes and tell you whether a post failed or the dirt under it left. That answer decides everything that follows, and getting it costs nothing.
Anglin's crews have been setting piers under metro Atlanta structures since 1930.
If the house is showing the same thing the deck is, that's a different conversation, and signs of foundation problems is the place to start.
Call 770-422-2924 for a free look.