The three biggest causes in the Triangle are expansive clay soil (swells wet, shrinks dry), poor drainage that saturates the perimeter, and tree root activity that pulls moisture from one side of the footing. Older Raleigh and Durham neighborhoods on Piedmont clay see the most seasonal cracking. Not every crack is structural - width, orientation, and progression matter more than presence.
The three biggest causes in the Triangle are expansive clay soil (swells wet, shrinks dry), poor drainage that saturates the perimeter, and tree root activity that pulls moisture from one side of the footing. Older Raleigh and Durham neighborhoods on Piedmont clay see the most seasonal cracking. Not every crack is structural - width, orientation, and progression matter more than presence.
The Triangle sits on expansive Piedmont clay. When it rains heavily in spring, the clay swells and pushes up on footings. In dry summers it shrinks and pulls away. That cycle, repeated for decades, is enough to crack any foundation not designed for it.
Older neighborhoods (Oakwood, Five Points, Trinity Park, downtown Chapel Hill) were built before modern soil analysis was standard. Their foundations move with the soil every year.
Hairline vertical cracks in poured concrete under 1/16" are usually shrinkage and cosmetic. Stair-step cracks in brick veneer wider than 1/8", horizontal cracks in a foundation wall, or any crack that grows visibly over 6 months should be evaluated by a PE. Bowing or leaning foundation walls are urgent.