Signs of a sinkhole under a house, and how inspection works
When to look harder
A county tier tells you whether the rock can form sinkholes, not whether one is under a given house. If the county is rated sinkhole country or has some sinkhole ground, the next steps are cheap: look the address up on your state geological survey's sinkhole or karst map, and look at the house and lot for the signs below. An inspection is the step after that.
Signs at the house
- New cracks in interior walls, especially stair-step cracks in block or brick, or cracks that widen.
- Cracks in a slab floor, or tiles that lift or crack in a line.
- Doors and windows that start to stick or no longer latch.
- Gaps opening where walls meet floors or ceilings.
Each of these also has ordinary causes, such as expansive clay, poor fill or plumbing leaks. On karst ground they are worth an expert opinion instead of a patch.
Signs in the yard
- A round depression that deepens, or a circular patch where grass or shrubs wilt.
- Water ponding where it never used to, or a pond that drains suddenly.
- Fence posts, trees or poles that start to tilt.
- Exposed foundation edge where soil has dropped away.
What an inspection does
A sinkhole investigation is done by a geotechnical engineer or professional geologist, not a general home inspector. It usually starts with a site visit and a look at the cracks and the lot. Ground penetrating radar can then map soft or disturbed zones a few metres down, and borings, often with standard penetration tests, measure how firm the soil is above the rock and whether there are voids or raveling. The result is a written report that says whether sinkhole activity is likely, and if so what repair it would take, commonly grouting or underpinning. In Florida, that report is also what an insurance claim rests on; see Florida sinkhole insurance.
If a hole opens
Keep people and pets away, and do not try to fill it. If it is near the house, a road or a utility line, call your local emergency number or building department, then your insurer.
Where to go next
See how it varies: Izard County, AR, Southampton County, VA, Elmore County, AL.
No limestone, but still holes: pseudokarst explained · How SinkholeOdds rates a county