Bowing, leaning or bulging in external walls are a result of decreasing wall stability, these defects are often a symptom of:
- Prolonged vibrations from heavy traffic or plant machinery
- An increase in the floor loads (for example where additional floors have been added to an existing building)
- The original walls being insufficiently thick in comparison to the building height
- A lack of restraint between the external walls and the floor joists, beams and partitions
Bowed, leaning or bulging walls occur more regularly in older buildings, particularly those built prior to 1914. Most commonly these properties will also be semi-detached, extended to three storeys, or end-of-terrace.
These types of properties are more prone to a decrease in wall stability because they will typically have solid walls (rather than cavity walls) which may have inadequate lateral restraint, a symptom of the construction methods of the time.
Typically, modern construction methods make use of metal strapping which connects the floors and roof to the external cavity walls. Additionally the internal walls are connected to the external walls.
You will often be able to identify a bowed, leaning or bulging wall through visual examination. Cracks may be evident at the connection of internal walls and floors with the external wall. It is important to note however, that a bowed wall without a crack will still require the same consideration as it is a dangerous fault.
In all instances, it is important to have a surveyor conduct the same accurate examination of the defective wall, taking into consideration the following points:
- The thickness and height of the wall
- The method of restraint
- The amount the wall is out of plumb
- The length, width and position of any fractures – both internally and externally
- General state of repair or disrepair
- Evidence of historic filling of gaps between internal finishes and external wall
- The number of openings and piers in the defective wall
The rule of thumb is that remedial measures will certainly be required when the amount of lean in the full wall height exceeds 1/6 of the thickness of the wall at the base.
There are a number of ways in which external walls can be restrained to prevent further bowing, many are disruptive for the homeowner and consequently more expensive and aesthetically unfavourable, for example channel sections or brick buttressing. Remedial wall tying is a less invasive, quicker and a more cost effective method for domestic structural repairs.
Remedial wall tying has been used to repair bowed, leaning or bulging walls since the early 19th Century. Early wall ties take the form of cast iron bosses (known as pattress plates) and were connected by tie rods to the opposite wall of the building, in an attempt to hold the walls vertical. Over the years, corrosion of these iron bosses has been known to cause damage to the surrounding stonework, so it is important to have these checked by a surveyor if they exist in your property. This early form of wall tying was largely phased out for domestic use from the 1940s.
Modern day wall ties are much less invasive for property owners. The Helibeam System of structural repair can be used to provide horizontal restraint in the external wall including BowTies and BowTie HDs to provide lateral restraint, and grouted CemTies are used to reconnect the internal and external walls. Depending on the cause of the bowing, HeliBars can be grouted into slots (normally the mortar beds) across the crack to assist in providing simple, permanent and non-disruptive stabilisation of the wall.