A linden tree planted just four meters away from a house can cause one of its corners to sink by several centimeters over the course of a decade. This isn’t due to the tree’s weight or its roots pushing against the walls. Instead, it’s caused by the tree’s water consumption, which dries out the clay soil beneath the house’s foundation. This drying leads to soil shrinkage, which can cause the rigid walls to crack as they settle unevenly. This process is known as clay shrinkage and swelling, a natural phenomenon in certain types of soil. Clay soils contain minerals that can absorb water between their layers, acting like tiny sponges. When water is present, the soil expands, but when it dries—such as during the summer or due to tree roots drawing moisture away—the soil contracts. This expansion and contraction mainly affects the top few meters of soil, which is where many older homes, especially those built before the 1990s, have their foundations. These homes often lack prior soil studies, making them more vulnerable to these changes. The movement of the soil isn’t uniform under a house. For example, the south-facing side of a building dries out faster than the north-facing side due to direct sunlight. A tree planted nearby can make this imbalance worse, as its roots can draw moisture from the soil over several meters, drying the area closest to the tree. Meanwhile, a leaking gutter or a waterproofing issue can cause the opposite side of the house to become waterlogged. This difference in soil moisture creates uneven movement: one side of the foundation may sink while the other remains stable or even rises slightly. Similar effects can be caused by impermeable surfaces like terraces or paved areas, which prevent rain from reaching the soil and create drier zones near the foundation. This uneven settling is known as differential settlement. One corner of the house may sink by a few millimeters to several centimeters, while the rest of the building remains relatively stable. The walls, unable to bend, eventually crack at the most stressed point. These cracks typically follow the joints between bricks or blocks, forming a diagonal pattern with a step-like appearance. This kind of crack is a telltale sign of foundation movement caused by clay shrinkage and swelling. Other signs, such as doors or windows that stick during dry periods and then open easily in winter, or a garage floor that separates from a wall, can also indicate this issue. However, only a professional assessment can confirm the exact cause of such cracks. Older homes are especially at risk. Many were built with shallow foundations and without protective voids or proper drainage, making them more sensitive to soil moisture changes. The location and design of a house, along with the surrounding landscape, also play a role. In France, this phenomenon is mapped at the commune level, with risk levels from low to high available on the Géorisques website. Millions of homes in the country are located in areas with medium or high risk, making clay shrinkage and swelling one of the leading causes of home insurance claims. Planting a tree with high water needs near an older home on clay soil without proper foundation protection can combine multiple risk factors. Proper planning, including soil diagnostics and urban planning guidelines, usually specify safe planting distances based on the tree species and its mature size.