The warning signs of expansive-clay damage, explained

Stair-step cracks

Diagonal cracks that follow mortar joints in a stair-step pattern, rather than running straight through brick or block, are the single most cited sign of differential foundation movement from expansive soil. A crack under about a quarter inch, stable over a few months of watching, is common and usually cosmetic. Wider than a quarter inch, wider at one end than the other, or still growing - that's worth a professional look.

Sticking doors and windows

Frames that stick seasonally, especially worse after a wet spell followed by a dry one, mean the structure around them is shifting with the soil's own wet-dry cycle. Isolated to one door in an old house, it's often nothing. Multiple doors and windows, all on the same side of the house, tracking the weather - that's a structural pattern, not a settling-house quirk.

Sloped or uneven floors

A floor that measurably slopes in one part of a house but not another usually means the foundation underneath it has moved unevenly - exactly what happens when soil under one section of a slab swells or shrinks more than the soil under another. A marble or ball rolling consistently toward one spot is a rough at-home check; an actual measurement is what a foundation contractor uses to quantify it.

What to do if you see more than one

Two or more of these signs together, in a county reading "High" or "Very High" on this site, is worth a geotechnical report ($1,000-$5,000) before anything structural is decided. One sign alone, in a "Low" or "Moderate" county, is more likely ordinary house settling than expansive soil - but the report is still the only way to know for certain.

Where to go next

Real counties this plays out on: Orleans Parish, LA, Coos County, OR, Monroe County, FL.

Moisture management: the cheap fix that works on any soil · Geotechnical report vs. foundation repair: what you need