What Causes Cracks in Walls and Ceilings? — A Homeowner's Guide to Structural Risk

Thermal movement. Brick, stone, and mortar all expand and contract with temperature change. In properties built with lime mortar — the majority of pre-1920s London stock — this movement is accommodated by the mortar itself. Hairline cracks at mortar joints are the normal result and are cosmetic.

Drying shrinkage. New plasterwork, render, and concrete all shrink as they cure. Fine map cracking or hairline cracks in relatively new work are usually this process and are not structural.

Clay shrinkage and heave. London clay — present across much of South and East London — shrinks in dry conditions and swells when wet. Properties on clay near trees are particularly susceptible. Seasonal clay movement causes cracking that follows a characteristic diagonal pattern, often at the corners of windows and doors.

Settlement. Most London properties have already settled fully — the majority of settlement occurs in the first years of a building's life. New cracking in an established property may indicate a new load, a drainage failure, root activity, or nearby excavation.

Lintel failure. Victorian and Edwardian terraces often have brick arches or early steel lintels over window and door openings. When these deteriorate, diagonal cracking at the corners of openings is the typical result.

Structural alterations without engineering. Load-bearing walls removed without proper structural design are one of the most common causes of structural cracking in London homes. If you are buying a property where a previous open-plan alteration has no documentation, a structural inspection is advisable.