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Property Surveying Blog
Written by Tughan Musa

Have you ever wondered why your wall appears to have a bulging beer belly? Bulging, bowing or leaning walls are one of those peculiar issues. It is a problem that can affect any solid masonry or cavity wall and may occur for a number of reasons.

Why Do Walls Bow?

Bowing walls occur more frequently in older buildings, particularly those built up to the Edwardian period.  The most susceptible are semi-detached, extended storeys and end of terrace properties.

Bowing in external walls can be the result of a few different symptoms, but it’s always due to a decrease in wall stability whereby the walls were never properly tied into the floor or roof structure in the first place, or were just cheaply built.  Solid walls as opposed to cavity walls may have inadequate lateral restraint, symptom, of the construction methods of the time.

How to identify it?

You will often be able to identify a bowed, leaning or bulging wall through visual examination. A bowing wall will have an obvious bulge. In older properties ‘spreader’ plates will be visible. These were retrospectively fitted to restrain the wall.

What are the causes?

Poor Building Practices

Older buildings are susceptible to wall distortion due to lower standards and inferior building knowledge in that time. Typically, there was a lack support and restraint, e.g., walls were often butted up to each other, bonding was minimal, and floor joists would have no lateral ties to support the wall, all of which would not pass todays building regulations.

Poor practices isn’t exclusive to the by gone era. Modern thoughtless alterations can result in restraining elements being removed without providing and alternative solution. One common example is the removal of a chimney breast to increase the floor area. The problem is, chimney breasts provided more than just heating for the Victorians, they also gave the wall a buttress style wall support.

Inadequate Thickness

If a wall is tall and thin it will have greater tendency to bow under applied load as opposed to shorter and thicker walls. The calculation for the relationship between a walls height and thickness ‘Slenderness ratio’ has improved over the last 50 years.

Lack of Restraint or Support

A large unsupported area of wall will tend to lean. Current statutory requirements are that walls are fully tied in together or supported by the provision of buttresses.


Walls can also bow outwards because they are overloaded having been built too thin, botched structural alterations or as a result of increase in floor load (where for example additional floors have been added to an existing building).

The most common cause from lean is ‘roof spread’ which happens when there is a failure to adequately support the main rafters. This occurs when the ceiling joists are no longer holding the walls together, pushing the upper section of the wall outward.

Bonding Failure

Solid walls were sometimes built with small embedded bonding timbers, in which over time can rot and deteriorate, causing the wall to bulge.

Tree Roots

If you have trees or shrubs growing near a wall, the roots may cause the walls to bow. Some roots can exert a lot of pressure against walls and grow significantly long.

Heave and Subsidence

Movement from both heave (expansion of soil normally caused by removing a nearby tree) and subsidence (shrinkage of soil) can damage the integrity of the wall resulting in bowing.


If over time the bowing wall is not repaired, snow, water or ice can accumulate and cause the mortar and brick to deteriorate and further weaken the structure risking collapse.

Where walls have bowed due to excessive loadings, some form of additional support will need to be provided and a structural engineer consulted. Some thin walls may need to be rebuilt entirely or installing a steel beam can divert the loadings.

Walls suffering from a lack of restraint can be secured to the upper floor joists or roof structure by building in metal ties — a modern variation on traditional S or X iron tie bars (below) that can be seen adorning the walls of many an old cottage.

Sometimes a wall will have ‘come loose’ because the floor joist ends that used to hold it in place have rotted through. The rotten timbers must be cut out, the cause of dampness remedied, and the ventilation improved, before defective lengths can be replaced with new pre-treated timber protected by a damp-proof course.

Similarly, where the roof has pushed out the walls causing them to spread, the solution is to provide additional restraint such as new ceiling joists or collars, and, in serious cases, to rebuild the upper wall.

If you suspect your wall is bowing, we would be happy to assist, feel free to give our team of surveyors a call now.