Numerous things related to the geology and climate in Madison are to blame for the widespread foundation problems. We’ll explain each of these factors in-depth below and the effects they have on the concrete under your home.
The soil throughout Madison and the rest of Dane County is varied, but much of Dane County falls in the Batavia-Houghton-Dresden soil association, which is poorly drained and considered expansive.
Other areas are underlain by silt loam, which has a higher ratio of clay and silt and little sand to aid in drainage. Expansive soil swells and shrinks when it gets wet due to its abundance of clay, and the resulting ground movement can create instability under and around your foundation.
During rainfall, runoff soaks between the fine clay and silt particles and causes the ground to expand.
The swelling soil places excessive pressure on your slab and foundation walls, often creating enough stress to crack the concrete and cause structural damage and even foundation failure.
During the drier winter months in Madison, the soil shrinks and can pull away from the concrete, leaving it without support.
This process rarely occurs uniformly beneath your home, so your foundation regularly sinks into the earth unevenly when the soil dries at varying rates. The result is differential settling, which can cause significant foundation damage and necessitate structural repair.
Lastly, Madison’s silty and clayey soil absorbs and retains water readily, as capillary action keeps water suspended in the gaps between the small particles.
The moisture from runoff is held against your foundation for prolonged periods and eventually seeps through cracks or pores in the concrete. Once it enters your under-home area, it causes water damage, promotes mold growth, and contributes to several other moisture-related problems.
The problems with expansive soil are made significantly worse with excessive rainfall and cyclical rain patterns when the ground moves from wet to dry and back again rapidly. Unfortunately, both of these conditions are present in Madison.
The city receives just over 36 inches of rain annually, which is only slightly above the national average.
However, the summer months bring more than double the monthly average rainfall the rest of the year. The concentrated precipitation from April to September keeps the ground saturated for long periods, increasing the risk of the ground swelling and placing undue hydrostatic pressure on your foundation.
Additionally, the rain in the winter is minimal, and the average temperatures below freezing keep the snow from melting and saturating the soil.
As a result, the ground is given the opportunity to dry, which contributes to the risk of differential settling. The cyclical nature of the soil’s moisture content throughout the year is detrimental as well, as the frequent changes promote ground movement and foundation instability.
Flooding is a problem throughout much of Madison. The concentrated rainfall in the summer and early fall can easily overwhelm the city’s storm drains and back up to the surface. Heavy rain can also overfill Lake Mendota and Lake Monona, causing an overflow.
The strip of land between the two bodies of water is at the most severe risk of flooding, but much of the rest of the city experiences flooding regularly as well.
Flash floods saturate the soil to the extreme, causing maximum swelling and stress on your foundation.
Additionally, floods contribute to leaking under your home. Most houses in Madison are built with basements because the frost depth is so deep, and basement walls and slabs are naturally prone to water intrusion.
Flash flooding increases the risk of water and water vapor accumulating in your basement or crawlspace, causing a variety of potentially severe problems.
Lastly, home foundations in Madison are often affected by frost heave, which is when the moisture in the ground freezes, expands, and places additional stress on your foundation walls.
The frost line in the Madison area is between 48 and 60 inches deep, meaning the ground freezes to a depth of at least four feet throughout the city. The additional pressure created by the solidification of the soil’s water content can promote structural cracks and stability issues under your home.