Wall ties are an unseen component found in cavity walls. A cavity wall is basically two different walls, usually an outer wall and an inner wall, separated by a gap or cavity. This design helps to improve insulation and prevent moisture from penetrating the interior of the building. The wall ties connect the two separate walls to each other, therefore giving them stability and strength. Wall ties have actually been used in construction methods since the 1800’s, and by 1945, they had become a standard part of cavity wall construction, which was the method used for most houses as it was proven that homes with cavity walls were warmer and drier.
Since then, filling the cavity wall with insulating material has become an increasingly popular way to conserve heat within the home. Just because wall ties are invisible from the exterior of a building, it does not mean that they are not crucially important! Poorly installed wall ties that have not been installed to the correct density and pattern can lead to severe structural problems.
How do wall ties function?
The wall ties are inserted during the construction of the two leaves at regular intervals, and the ends of the wall ties are embedded in the mortar of both leaves at regular intervals to a depth of 62–75 mm. Wall ties can be used for cavity walls made from brick, timber, and steel. Today, cavity walls are being built wider so that they can accommodate thicker insulation as energy efficiency improves.
Modern cavity walls vary in depth from 50 to 450 mm, and it is crucial that the correct wall ties are used. The wall ties must be carefully inserted at the correct density, and the minimum density as defined in Eurocode 6 is 2.5 ties per square metre. Additional ties must also be installed around openings and unbounded edges.
Cavity Wall Ties Design
The design of cavity wall ties has evolved over time to enhance their performance and durability. In the early days, they were made of terracotta, wrought iron, or cast iron, but later, galvanised mild steel became the preferred metal. It was soon discovered that this was not a good choice as it was found to start corroding after about 15 years, although it had been hoped that it would last the lifetime of the building. Since the early 1980’s, wall ties have been used that consist of a triple zinc coating on a stainless steel tie, and this composition is approved by British Standards.
Here are some key aspects of their design:
● Material: Traditionally, wall ties were made from galvanised steel, but stainless steel is now more commonly used due to its improved corrosion resistance.
● Shape and Size: Wall ties come in various shapes and sizes to suit different types of construction. Common designs in use are butterfly ties, double triangle ties, and wire ties. The size and shape of the tie depend on the width of the cavity and the type of walls being connected by the tie.
● Corrosion Protection: Modern cavity wall ties are either coated or made from corrosion-resistant materials. This is very important since corrosion weakens the ties; hence, the integrity of the wall structure is jeopardised.
● Thermal Efficiency: Some cavity wall ties are designed to minimise thermal bridging, which can reduce the energy efficiency of a building. Such ties normally have a plastic component that offers insulation.
Cavity Wall Ties Installation
Proper installation of cavity wall ties is vital to ensuring their effectiveness. Cavity wall ties must be spaced correctly to provide adequate support. The standard practice is to place them at regular intervals, typically 450 mm vertically and 900 mm horizontally. Sometimes, closer spacing may be necessary when there are other specific conditions, such as high wind loads, etc.
Ties should be installed slightly sloping towards the outer wall to prevent moisture transfusion into the inner wall; they should also be adequately embedded into the mortar joints of both walls. During installation, the level alignment of the ties should be checked to be very sure that they are rightly positioned, as misaligned ties will result in uneven load distribution with potential problems for the structure. Different cavity wall ties require various methods of fixing, with wire ties normally twisted into position and flat ties embedded in the mortar as the walls are built.
Problems with Cavity Wall Ties
Despite their crucial role, cavity wall ties can encounter problems that may compromise the integrity of a building. Some common issues include:
● Corrosion: Probably one of the most common problems associated with installed cavity wall ties on older properties is that when they corrode, they lose their strength, leading to wall movement and subsequent cracking. This is particularly common in properties built before the widespread use of stainless steel ties.
● Inadequate Installation: Poor installation practices, such as incorrect spacing or alignment, can lead to ineffective wall ties. This can create structural weaknesses and make them more susceptible to damage from wind loads or other forces.
● Wall Tie Failure: In some cases, wall ties can fail entirely, leading to serious structural issues. This can be caused by heavy corrosion, improper installation, and unsuitable types of ties for specific construction.
● Detection and Repair: Cavity wall tie problems normally require specialist equipment and expertise to detect. The most common signs of wall tie difficulties are usually horizontal cracking within the mortar joints or bulging or bowing of the walls.
Cavitech-UK is a Sussex-based company that operates nationwide in cavity wall tie installation and replacement as well as insulation filling and extraction.