House settling in New Orleans

The ground under New Orleans moves

The City’s hazard mitigation plan describes subsidence, the sinking of the ground, as driven mainly by the drainage and oxidation of organic soils, natural compaction, compaction of aquifers, and dewatering. It states that houses without deep pilings are settling unevenly and cracking, and that ruptured water and sewer lines are among the effects.

Many New Orleans soils are soft, compressible and rich in organic material. A satellite study covering 2002 to 2005, published in Nature, found an average sinking rate near 0.2 inch per year, with some areas at about 0.8 inch (20 mm) per year or more, and the fastest areas were largely former wetlands that had been drained and built on. Those are historical measurements from that period, not current rates for your street.

The practical point is that settlement is uneven. One corner of a house can move more than another, and that difference, not the overall sinking, is what cracks plaster and sticks doors.

Signs worth noting

• New or widening cracks in plaster, drywall or masonry, especially diagonal cracks at door and window corners.
• Doors and windows that begin to stick or no longer latch. See sticking doors.
• Floors that slope or dip. See sagging and sloping floors.
• Gaps between baseboard and floor, or between a porch and the house.
• Piers that lean or crack, or gaps between a pier and the beam it supports.

None of these is proof of settlement. Moisture, decayed wood and termites can produce several of the same signs. Write down what you see.

What you can do before you call anyone

1. Start a dated log of floor readings, cracks and door behavior, using our printable floor, crack and door log. It shows whether movement continues.
2. Check for water. The City notes that ruptured water and sewer lines are connected to subsidence damage. A leaking line can also wet the ground or wood. Watch for damp spots, unexplained water use, and slow drains.
3. Look at drainage. Historic-building guidance points to grading and downspouts that carry water away from the foundation.
4. Photograph cracks with a ruler in the frame.

When it is time to ask a professional

Ask promptly if movement is changing over days or after a storm, if a floor feels soft, or if cracks and jamming doors appear together. Who you ask depends on what you find: a foundation or leveling contractor for supports, a licensed pest control operator for termites, a plumber for leaks, and a structural engineer for significant or unclear conditions. Structural work generally needs a City permit; see structural repair permits.