What Is The Difference Between Settlement and Subsidence?
Settlement usually occurs in new or relatively new buildings or new additions to
existing buildings. This is due in part to the compaction of the subsoils because of the weight of the new structure, and partly due to the drying out of the various materials, that will dry at different rates. Normally, the movement will stop after a period of time, with no additional works required other than filling and redecoration of the cracks. Most buildings move to varying degrees due to seasonal movement. This is due to differences in temperature and humidity. Older properties with lime mortar were able to flex and move, so when cracks appeared, say in summer, they were able to close up again in winter.
Subsidence on the other hand is more serious, and is the result of the ground beneath the foundations not being able to support the weight of the building. This is evidenced by cracks at weak points of a building, usually around window and door openings. These cracks are usually diagonal and extend through the walls, being seen on the inside and outside wall surfaces.
Trees and clay subsoil are noted for being a contributory factor in causing subsidence. This is because trees remove moisture from the subsoil (clay), which then shrinks causing the foundations to sink. Another cause is defective drains, where water erodes the subsoil which in turn is unable to support the weight of the building, causing it to sink.
The opposite of subsidence is heave, where the ground swells due to the absorption of water causing buildings to rise.