What a Foundation Elevation Survey Shows

A foundation elevation survey shows how the height of your floor varies across the house, point by point, in tenths of an inch. The readings get plotted as a map, and that map is what an inspector hands you at the end of a visit. It does not tell you how far the house has sunk since it was built, because nobody measured the slab the day it was poured. It tells you the shape the slab holds today, where the highs and lows sit, and how fast the floor changes between them. Most homeowners get the printout, find the scariest number on it, and stop reading right there. This guide is about reading the rest of the page, because the biggest number on it is almost never the finding.

What the printout actually is

The survey takes about an hour inside a typical home. A technician records the height of the floor at dozens of points against a reference point picked at the start, often near the front door, and notes anything that would skew a reading, like the step into a sunken living room or the thickness change where tile meets carpet. What comes back is the printout, a floor plan with a number at each measured point, usually shaded so the high and low areas stand apart at a glance. Read it the way you would read a topographic map. The numbers are heights, the shading is terrain, and the terrain is your slab. The measuring is our job, one piece of what the free inspection measures alongside crack mapping and drainage. Reading the result is yours, and it takes about five minutes once you know what the numbers are relative to.

What the numbers mean

Zero on the map is not sea level and it is not the original height of your slab. It is wherever the technician set the reference, and every other number is a comparison against that one spot. A reading of minus 1.2 means that point sits 1.2 inches lower than the benchmark. It does not mean the floor sank 1.2 inches, and it does not mean it sank at all. Slabs are not poured perfectly flat, and a builder-tolerance dip that has sat unchanged since the concrete cured shows up on the map right beside movement that happened last spring. The map cannot tell those two apart on its own, which is one reason a single survey is a baseline rather than a verdict. It also means you cannot compare two surveys number for number if they used different reference points. The shapes get compared, not the digits.

Differential readings matter more than the total spread

The first number most people compute is the absolute spread, the highest reading minus the lowest. It is also the least useful number on the page. What loads the structure is differential movement, the change between nearby points over a known distance, which is the slope of your floor. An inch and a half spread across fifty feet of house works out to a grade of a quarter percent, a plane so gentle most feet never notice it. The same inch and a half packed into ten feet is a bend, and bending is what the frame above the slab feels. So when you look at your printout, do not hunt for the biggest number. Hunt for the shortest distance between two very different numbers. That is where the shading changes fastest, and it is the first place we look too.

Why one low corner outranks a whole-house tilt

A slab can move two ways, and the map separates them. It can lean as one rigid plane, the whole house tilting slightly like a book on a wedge, or it can bend, with part of the floor curving out of line with the rest. A plane tilt carries surprisingly little internal stress. Nothing is being curved, so the frame stays close to square and the drywall mostly keeps quiet. A low corner is bending. The slab curves around the edge of the drop, and that curve is what cracks sheetrock at door corners, racks frames out of square, and separates baseboards from the floor. On the printout, a tilt reads as shading that changes evenly from one side of the house to the other, while a bending corner reads as contour lines crowding together in one spot. A survey with a mild overall lean is often a healthier survey than one with a smaller spread packed into a single corner, which is exactly why the biggest number is not the verdict.

What a normal survey looks like

Most of the homes we measure hold their readings within about an inch across the whole house, and a good share of that is construction, not movement. Central Texas clay adds a seasonal breath on top, so a modest spread near the perimeter that comes and goes with the weather reads as normal here. About a third of our inspections end with no repair needed, and a survey inside the normal band is a common reason we say so. Whether readings past that band are acceptable is a measured question with published limits for bending and tilt, and that evaluation is its own subject, worked through in the published limits for foundation movement. The shape also hints at cause before anyone opens a wall. Lows at the perimeter point toward settlement, a high center points toward heave, and settlement and heave draw different shapes on the survey.

What to do with your survey

Keep it. A dated elevation map is the most useful document your foundation can have, because the second survey only means something against the first. Ask the inspector two questions before they leave, where the zero point was, and where the tightest gradient sits. Those two answers are the whole map in miniature. Our yearly performance follow-up inspection re-measures against the baseline, which is how bounded seasonal cycling gets separated from movement that keeps going one direction. If the map does show real directional movement and a repair gets scoped, we underpin with steel and hybrid piers at $600 to $1,000 each, and the piers carry a lifetime transferable warranty. And when a lender, a dispute, or an unusual structure means the map needs an independent stamp rather than a contractor's findings, when the survey should go to an engineer covers what that report adds and what it costs. The survey itself is free, run by ICC-certified inspectors, and the printout is yours either way.