Warning signs
Uneven floors: foundation problem or not?
People usually discover this one by accident — a dropped pen that rolls, a washing machine that walks, furniture that rocks in a room where it never used to. The useful question is not whether your floors are level, because they almost certainly are not. It is whether the pattern of unevenness means anything.
Floor slope is meaningful only in context — the age of the house, how it was built, and whether the deviation is changing. Nothing on this page can establish that for your home; a measured survey can.
Almost no floor is level
Houses are built by people to tolerances, on ground that moves. Framing lumber dries and twists. Soil compresses under load. A floor that reads dead flat is the unusual case, not the normal one, and homeowners who start measuring are often startled by what they find in perfectly healthy houses.
So the number on its own settles very little. What a professional is looking for is the shape of the deviation across the whole floor plan — and how that shape has changed.
The pattern is the diagnosis
When elevations are plotted across a house, a few characteristic shapes appear, and each points somewhere different.
- Low at one corner, rising steadily away from it. The classic differential settlement pattern. Usually pairs with stair-step cracking in the brick on that corner and doors sticking on that side.
- Low all the way round the perimeter, higher in the middle. Very common in Texas expansive clay, where the soil at the edges of a slab dries out and shrinks faster than the soil under the center.
- High in the middle, sloping away in all directions. Often heaving rather than settlement, and frequently traced to water getting under the center of the slab — where it is normally driest — via a plumbing leak.
- A ridge or step along a line. Sometimes a change in what the house is bearing on: the boundary between cut and fill on a graded lot, or between two different soil types.
- Random small variations with no gradient. Usually construction tolerance and framing, not the ground.
You cannot see these patterns by walking around. They emerge from a grid of measurements, which is why the elevation survey matters so much more than any single observation.
How to get a rough sense yourself
Not a substitute for measurement, but it tells you whether there is something to measure.
- Roll a marble or a golf ball in several rooms, in two directions each. Note where it consistently goes. Consistency across rooms is the signal; one room is just one room.
- Use a long level or a straight board — four feet minimum — and check in several places rather than one.
- Look at the baseboards. They were installed following the floor, so a gap that opens and closes along a single wall suggests the floor moved after the trim went on.
- Check doors against their frames. An uneven gap along the top of a closed door is a rough plumb-and-level reading you already own.
- Write down what you find, with the date. Repeating this in six months is what turns observation into evidence.
Slab versus pier and beam
The same symptom means different things depending on what is under the floor.
On a slab, the floor and the foundation are the same object, so floor elevations are foundation elevations. Unevenness is a fairly direct report of what the slab is doing, and correcting it means supporting the slab from underneath — piering or underpinning.
On a pier and beam house the floor sits on a wooden structure above the foundation, so unevenness can originate anywhere in that stack: a settled pier, a sagging or rotted beam, an over-spanned joist, or the ground under the piers. That is more diagnostic work, but it also means the fix is frequently cheaper — the structure was designed to be shimmed and adjusted. More on crawl space repair →
Before assuming soil, get a hydrostatic plumbing test. A leaking supply or sewer line under a slab wets the ground beneath it and produces exactly the high-in-the-middle elevation pattern described above. It costs a few hundred dollars and either rules a leak out or changes the whole repair plan — including who might pay for it.
When unevenness is worth acting on
Slope by itself is rarely urgent. It becomes worth moving on when it appears alongside something else: cracks that are actively widening, doors that have gone from sticking to not closing, a wall that is visibly out of plane, or a measurable change between two surveys. A house that has been two inches out for forty years is telling you something very different from one that has moved half an inch since last year.