- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 16 Jun 2018
Wall ties are an essential component of a cavity wall, helping to keep the structure safe and stable. Although cavity walls have been constructed for centuries, the use of metal ties to connect the two skins only emerged in the second half of the 19th century, and has been a standard bricklaying practice in the UK since the early-20th century.
Wall ties are strips or bars, made of metal that span the cavity and tie the internal and external walls of bricks or blockwork together. The ends of the tie are designed to lock tightly into the mortar. The ties are also designed to prevent water transfer from the outer to the inner leaf of the wall, this often takes the form of a twist in the tie or, if a wire tie, corrugations formed in the wire.
Wall ties are important because of the relative thickness of the outer skin in relation to its height. Unlike the inner skin, the outer skin may not benefit from the intermediate support of floor joists, ceiling joists and the roof which bear into it and help to make it rigid. This horizontal lateral restraint ensures that the inner skin remains stable, as does vertical lateral restraint from internal walls that divide rooms and brace the inner skin.
Cavity wall ties transfer the stability of the inner skin to the outer skin, effectively combining them to make a wall with greater overall thickness.
The cavity width and the width of each wall leaf determine the appropriate spacing of the wall ties. These can vary from a 900mm x 450mm staggered pattern to as close as 450mm x 450mm pattern if required in specific parts of a wall, for instance around windows. The density of the wall tie installation must also take into account predicted wind loadings, and must therefore be designed for the specific geographic conditions of the site.
In order to allow the inner and outer leaves of a wall to move differentially as they warm and cool as well as through natural settlement, wall ties need to be flexible. Embedding ties at building corners is generally avoided as stress fractures may be incurred.
Steel, and traditionally iron, are the most common materials used to make wall ties. These eventually become subject to corrosion in damp conditions so are often galvanized to try and prevent this. Older buildings that incorporated mild-steel ‘fishtail’ ties and galvanized wire ‘butterfly’ ties are increasingly at risk of corrosion.
Modern practice is to use stainless steel ties to try and limit the risk of exposure to water and chemical attack from cement. Insulation retaining discs made from robust polypropylene are used to apply a firm grip onto each wall tie.
The main cause of failures is the rusting of metal ties, although there can be other causes, such as:
- Failure to properly bed the tie in the mortar joint.
- Poor quality mortar reducing the bond between tie and mortar.
- Not installing the requisite number of ties.
Read more about wall tie failure.
 Related articles on Designing Buildings Wiki
- Building damp-free cavity walls.
- Cavity wall.
- Cavity wall insulation.
- Cavity tray.
- Damp proof course.
- Diaphragm wall.
- Herringbone strut.
- Preventing wall collapse.
- Wall tie failure.
- Wall types.
- What are walls made of?
 External references
Featured articles and news
Balfour Beatty fined £500,000 for exposing workers to hand-arm vibration.
James Brokenshire launches a consultation on banning combustible cladding.
A year after Grenfell, we have a collection of 30 articles telling you everything you need to know.
ICE publish a policy paper on the UK’s future interconnectivity with the EU and the challenges for infrastructure.
Detailed guidance about construction waste management.
The changing identity of London communities in the face of rapid urbanisation.
Can you help? We have 300 industry acronyms beginning with 'C' but none beginning with 'Y'.
From the sinister Carceri d’Invenzione to the triple portrait of Sir Watkin Williams-Wynn and his Grand Tour travelling companions.
BSRIA launch the 5th edition of the Design Framework for Building Services (BG 6/2018).
Stella Rimmington famously said the construction industry was just as tricky as the KGB.
Construction site visitor cards are to be withdrawn.
3 WTC opens, RSHP’s first built project in New York.