CAVITY WALL TIE FAILURE

Since the 1920's, most properties in the UK have been constructed with the main walls incorporating a cavity. A cavity helps reduce the risk of damp penetration and improves insulation standards.

The two leaves of brick or blockwork are held together by metal ties, stabilising the structure of the wall. Over time, these "ties" can corrode and fail allowing the inner and outer leaves of the wall to become unconnected and therefore unstable.

Standards of galvanising to wall ties were improved in 1981 and properties built before this date are possibly at greater risk to wall tie corrosion. Some types of mortar can be more corrosive and the type, height and location of a property can affect its vulnerability. Sometimes properties are constructed with insufficient wall ties.

Research by the BRE (Building Research Establishment) www.bre.co.uk has shown that perhaps two million dwellings suffer from cavity wall tie corrosion or failure.

Left to develop, horizontal cracks may be the first signs of a problem but corrosion can occur without external evidence. Older types of cavity ties can rust and expand causing movement and bulging of masonry, and possible eventual collapse in high winds.

Surveyors will look for evidence of deterioration or failure and will normally have local knowledge of this type of problem in a particular locality. When suspicions are aroused, a surveyor is likely to recommend closer examination of the cavity ties (probably by using a small optical instrument known as an endoscope) so that the extent of any problem can be ascertained.

A number of reputable companies specialise in the replacement of cavity wall ties and work can largely be carried out externally to minimise disruption and damage to the interior of the property.

It is always advisable to use an established specialist contractor who can offer a secure long-term transferable guarantee.