Cracking to low-rise buildings

Cracking within low-rise buildings of masonry construction is common, but many cracks and signs of minor-movement are not significant and do not require any action.

All buildings move to some extent and for a variety of reasons. This is a brief summary of the sorts of cracking that might be encountered during the survey of a house or flat, or which can be reported to us by concerned homeowners or businesses.


Ground-related movement

Many homeowners worry that any cracks they see result from subsidence, but it is not a particularly common problem. Subsidence is movement of a building due to the downward movement of the supporting ground and the opposite is heave, which is where the supporting ground swells and the building moves upwards.

Soil types that are highly shrinkable, such as clay, are more prone to subsidence and heave. Changes in water content can result from the weather, trees, defective drains or local changes in the environment.

Subsidence often causes diagonal cracking, with cracks often passing through bricks rather than following brick-joints. Floors may slope, and doors and window openings may become distorted.

The problem often arises due to inadequate foundations, so more commonly affects older buildings. The standard remedy was once to underpin, which is expensive work where extra depth of foundation is added. However, it has become quite common to repair the affected building structure above ground and found to not always be essential to underpin.


Shrinkage

A great deal of water is used in traditional masonry building construction. When a building is young shrinkage can continue for a few years, sometimes leading to cracking or gaps, which are rarely significant and can normally be filled, or ignored.


Thermal movement

Different building materials expand or contract with heat or cold at different rates. In warmer weather, you can often hear plastic gutters or eaves creaking as they warm or cool. Expansion and contraction due to thermal movement can lead to cracking, normally narrow, vertical cracks in brick or block walls. This type of cracking is not often serious and can be tolerated, or remedied by introducing an expansion joint or by stitching the cracks with stainless-steel rods.


Differential settlement

When a new building is constructed, it gradually settles upon the ground under its self-weight. If an extension is added to an older building, the extension may settle relative to the original structure, which has long-since stopped moving. This is known as differential settlement, and can cause cracks at the junction between the old and new structure. If the cracking is significant, but straight, then it can usually be filled and / or tied into the main structure. If the crack is mild, remedial action is probably not essential.


Overloading or lack of support

Cracks can occur because part of the structure of a building is overloaded or not properly supported. This might be due to a design failure, alterations, or because deterioration or a specific defect has altered or weakened part of the structure. Examples include removing part of an internal wall, or creating a new doorway; a rotted area of floor structure or roof structure caused by dampness or water penetration; or storing too many heavy items in a loft.

A common issue is with lintels spanning window or door openings. Many older buildings were constructed by building-off of wooden window frames, with the walls perhaps having timber lintels, steel flat bar lintels or no lintels at all. Problems often arise following the installation of PVCu framed replacement windows, which might be fitted without any regard to the support of the brickwork above the opening. Unreinforced plastic frames then enable the brickwork to settle across the opening, typically causing stepped cracking in the shape of a triangle.


Wall ties / embedded metal

Metalwork has commonly been used in building construction for many purposes, including structural beams, lintels and columns, wall ties, bolts, and frame-fixings for windows and doors. This metalwork has a tendency to corrode and the expansion of the metal due to rusting can cause cracking originating from the position of the metalwork concerned. Over a longer period, unrestrained walls can be significantly displaced, especially at the tops of walls.


Assessment of cracking

Assessing the likely causes of cracking generally requires a methodical and systematic approach, beginning with a site inspection to measure and record details. The likely reasons for cracking might be fairly clear, but it is commonly the case that a conclusive opinion cannot be given without the benefit of further investigations, which might involve a period of monitoring. It is almost impossible to state with any certainty that a crack is historic and non-progressive from a single visit: just because a crack is old does not mean that movement has stopped.

The Building Research Establishment has produced a standard method of classifying cracks in houses, using a scale from 0 to 5. This enables a standard approach to categorising and explaining the likely significance of cracks and what remedial action might be required.


Typical remedial actions

Remedial action for cracks varies according to the cause, extent and severity, as well as to some extent the tolerance of the building occupants. Some cracks might need no action, or perhaps routine filling and decoration, whilst other cracks might indicate the need to repair, strengthen, rebuild or underpin. There are a variety of effective systems for repairing brickwork, for example, which no longer require disruptive and labour-intensive rebuilding.

Contact us if you have concerns about cracking or other signs of building movement and one of our Chartered Building Surveyors will be pleased to assist.