Sinking slab vs foundation problem: how to tell the difference

Sinking slab vs foundation problem comes down to where the movement is. It's the slab if walls are straight, doors work and the crack stays in the slab. It may be the foundation if you see stair-step wall cracks, sticking doors, or cracks running up the wall — call a structural engineer first.

New Orleans Concrete Leveling handles slab leveling — driveways, walks, patios, garage floors and slab floors — not foundation repair. So here’s an honest way to tell which one you’re looking at. This is general guidance, not an engineering assessment.

Signs it’s the slab only

• The crack is in the concrete slab and doesn’t continue into the walls.
• Walls are straight and free of new diagonal or stair-step cracks.
• Doors, windows and the garage door open and close normally.
• There’s a gap between the slab and the wall or porch — the slab moved, the structure didn’t.
• The drop is at an edge: the garage door, a downspout corner, the joint with the driveway.

These are leveling jobs: garage floor, driveway, patio, interior slab.

Signs it may be the foundation

• Stair-step cracks in brick or block walls, or diagonal cracks from door and window corners.
• Doors or windows sticking, or gaps at the top of doors that change over time.
• Cracks that run from the floor up the wall, or across the foundation itself.
• Floors sloping across the whole house, not just one room or addition.
• Gaps at the ceiling line or between walls and trim.

If you see these, get a structural engineer’s opinion before any contractor quotes a fix.

How New Orleans houses change the picture

Raised houses on piers or pilings. The main floor is framing on piers, and everything around it — walks, steps, patios, carport slabs — sits on soil. When that soil settles (the City of New Orleans puts average subsidence at about 0.2 inches a year), the concrete drops away from a house that holds still. That’s a flatwork problem. Leveling the house itself is a separate trade.

Slab-on-grade homes (common in Metairie, Kenner, Chalmette and the Westbank). The house slab and the flatwork were poured separately. A dropped driveway or patio beside a straight, trouble-free house is flatwork. Cracks through the house slab with interior symptoms are a foundation question.

Additions and converted garages. Often poured later on newer fill. A floor sloping only in the addition is usually a slab issue in that addition — see interior slab leveling.

Bottom line

Straight walls, working doors and a crack that stays in the slab mean flatwork — a leveling job. Stair-step wall cracks, sticking doors and cracks up the wall mean call a structural engineer first. For a free slab estimate, call (504) 517-8336 — free estimate within 24 hours.