Why houses settle in Lincoln
Clay that shrinks in dry weather. Most Lincoln homes sit on loess, a fine wind-blown silt, with clay below. USDA rates the clay subsoil of Wymore, the most common soil in Lancaster County, in the highest shrink-swell class. Crete, another common soil here, is also clay-rich below the topsoil. When clay dries, it shrinks and pulls away from the footing. That lets the house drop a little.
Dry years after wet ones. Lincoln averages about 29 inches of rain a year, but in the 2012 drought it got only about 19. Long dry stretches shrink the soil deeper than usual. Corners near large trees, south and west walls that get the most sun, and areas under eaves without gutters often dry out first. Those corners settle first.
Soaked soil in spring. The same soil is often saturated within one to three feet of the surface in March and April, according to USDA data. Soft, wet clay under a footing can squeeze out and let it sink, especially where a downspout or a low spot keeps one corner wet.
Frost. The City of Lincoln asks for frost-free footings at least 36 inches deep for decks. Older porches, steps and add-ons built on shallow footings can heave in winter and drop in spring.
Housing age. About 1 in 8 Lincoln homes was built in 1939 or earlier, and the median home was built around 1982. Older homes have seen many cycles of wet and dry. Newer homes in growing areas sit on fill that is still packing down.
