Which Wall Tie Should You Use? Cavity Width, Exposure, and Remedial Tie Selection

Summary

Wall ties are the metal connectors that link the two leaves of a cavity wall, transferring lateral loads (wind pressure) from the outer leaf to the inner leaf while allowing vertical differential movement between them. Without adequate, correctly spaced, and properly corrosion-resistant ties, a cavity wall's outer leaf becomes structurally independent, vulnerable to overturning, bulging, and ultimately collapse in wind loading.

Tie failure due to corrosion was a major problem in UK housing built between approximately 1920 and 1981. Many of these properties used mild steel butterfly ties that have now corroded, expanded, and cracked the mortar joints — a condition known as tie failure or delamination. The prevalence of this problem in the housing stock is the reason that BRE Digest 329 was produced and that stainless steel became the standard material for new ties from the 1980s onward.

Cavity wall tie selection requires the designer or builder to balance several variables: cavity width, which determines the required tie length and load capacity; exposure zone, which determines the corrosion resistance class; structural requirements, which determine the load category (light, standard, or heavy duty); and any special conditions (insulated cavities, walls over 12m high, parapet walls) that require enhanced specifications.

Key Facts

• BS EN 845-1 — European harmonised standard for wall ties, lintels, hangers and brackets; all new ties for cavity walls must comply
• Standard tie frequency — 2.5 ties/m² for most domestic cavity walls; more specifically: 900mm horizontal centres, 450mm vertical centres (approximately 2.5/m²)
• Additional ties at openings — Extra ties within 225mm of an opening reveal, at 300mm vertical centres, to transfer lateral loads around window and door openings
• Stainless steel grades — A2 (304 stainless) for most applications; A4 (316 stainless, molybdenum-containing) for coastal/severe/very severe exposure zones; never use bright drawn steel (mild steel) or galvanised steel in new construction
• BRE Digest 329 — The key reference for corrosion risk assessment; defines exposure zones based on location (distance from coast, sheltered/exposed, pollution level) and classifies tie material requirements
• Cavity width and tie length — Tie must embed a minimum 50mm into each leaf; tie length = cavity width + 100mm; for example, a 100mm cavity requires a 200mm tie (100 + 50 + 50)
• Butterfly tie vs wall tie — Butterfly (twisted) ties are the traditional type used in older construction; they perform adequately in compression but are poor in tension; standard modern ties (fishtail, channel, or triangular pattern) provide both tension and compression load transfer
• Stainless steel fishtail tie — The dominant type in UK new-build; flat stainless strip with fishtail (leaf-shaped) ends for mortaring into beds; provides both compression and tension capacity
• Helical (spiral) remedial ties — Used for replacement of corroded original ties in existing cavity walls; drilled and grouted or mechanically fixed into the masonry rather than mortared in during construction
• Maximum vertical tie spacing — 450mm for standard domestic walls; reduced to 300mm for walls over 12m high and for parapets
• Drip feature on ties — All cavity ties must have a drip (groove or twist in the centre of the tie) to prevent water migrating along the tie from the outer leaf to the inner leaf
• Load categories — BS EN 845-1 defines minimum characteristic loads; the engineer specifies the load category for each tie position in engineered masonry; in standard domestic work, the standard tie specification covers most situations
• Timber frame construction — In timber-frame buildings with masonry outer skin, ties are fixed through the sheathing board into the structural studs; different tie types and spacing rules apply [verify with timber frame tie manufacturer data]

Quick Reference Table

Detailed Guidance

Tie Selection for New Build

For standard domestic new-build masonry cavity walls, the default specification is:

• A2 (Grade 304) stainless steel flat fishtail tie, length calculated as above
• Frequency: 900mm horizontal, 450mm vertical (2.5/m²)
• Additional ties at 225mm from reveals, at 300mm vertical
• All ties installed with drip feature pointing downward and centred in the cavity

The tie supplier's technical data sheet should confirm compliance with BS EN 845-1 and state the load category achieved. Ties must be selected to achieve the design lateral loads calculated for the wall panel dimensions.

Insulated cavities: Where the cavity is partially or fully filled with insulation board (rigid PIR or EPS) or mineral wool slab, the tie must be long enough to penetrate through the insulation and achieve the required 50mm embedment in each leaf. In full-fill installations, the insulation is typically fitted in sections between the ties as construction proceeds. Do not use ties that are too short to achieve the embedment requirement after allowing for insulation.

High-rise and exposed locations: For walls above 12m in height and for parapets (which are exposed on both faces), reduce vertical tie spacing to 300mm. This applies to domestic construction where a parapet wall exists, for example on flat-roofed extensions.

Exposure Zone Assessment

BRE Digest 329 (Cavity Wall Ties: Assessment, Installation and Inspection) is the key reference for UK corrosion zone mapping. The zone is determined by:

1. Location relative to coast: Within approximately 1–2km of the sea (very severe), 2–5km (severe), inland (moderate or sheltered)
2. Exposure to driving rain: Using METS (Meteorological Exposure by Topographic and Sheltering) assessment or simplified national exposure classification maps
3. Pollution level: Industrial and urban pollution can increase corrosion risk even inland

For most standard domestic new-build in England outside the coastal zone, A2 stainless is adequate. For coastal locations (Cornwall, Scottish islands, west coast of Ireland), A4 stainless is the correct specification.

Remedial Ties for Existing Buildings

Cavity wall tie failure in buildings constructed between approximately 1920–1981 is widespread. Typical indicators:

• Horizontal cracking in mortar joints at regular vertical intervals (typically 450mm — the original tie spacing)
• Visible staining or rust marks at mortar joint courses
• Any bulging or bowing of the outer leaf
• Confirmed by specialist survey (metal detection scan of tie positions, followed by mortar joint opening to inspect tie condition)

Remedial tie installation:

1. Survey: Identify all tie positions; assess extent of failure; check for localised vs widespread failure
2. Drill: Drill through outer leaf and into inner leaf at new tie positions; diamond drill bit at correct diameter for the chosen helical tie
3. Install: Drive helical ties into both masonry leaves; the spiral profile grips the masonry mechanically; some systems use an injected grout for additional bonding
4. Seal: Seal the drill hole entry in the outer leaf with a matching mortar
5. Original ties: In most cases, the corroded original ties are left in place (removing them requires cutting out mortar joints over the full elevation, which is very disruptive); they are stabilised by the new tie pattern

Helical tie products are available from suppliers such as Helifix, Rawlplug, and Cintec. Installation contractors must follow the system manufacturer's instructions for drill diameter, embedment depth, and tie density.

Butterfly Tie vs Standard Tie Comparison

Butterfly ties (twisted wire loops) were the standard type in UK domestic construction until approximately the 1960s–1980s. Their performance characteristics:

• Adequate in compression (wall panels pushing against each other)
• Poor in tension (outer leaf pulling away from inner under wind suction)
• Minimal resistance to differential vertical movement (the twist provides some flexibility)

Standard modern stainless steel flat ties (fishtail or channel section) provide:

• Both tension and compression capacity
• Positive drip feature
• Defined compliance with BS EN 845-1 load categories
• No corrosion risk in the service life of the building

Butterfly ties in original condition in pre-1981 buildings are a recognised failure risk, particularly in coastal environments. If a property in an exposed location is being assessed, the tie type and condition should be checked as part of any structural survey.

Frequently Asked Questions

How do I know if the cavity wall ties in an existing house have failed?

Typical signs: horizontal cracking in mortar joints at regular intervals (usually 450mm or 300mm vertical centres); any outward bowing or bulging of the outer masonry leaf; rust staining at mortar joints; visible separation of the outer leaf from the inner leaf at openings. A structural engineer or specialist surveyor should carry out a tie assessment — metal detector survey followed by mortar joint opening for visual inspection — before any major refurbishment or retrofit.

Can I use galvanised ties for new cavity wall construction?

Galvanised ties are not recommended for new-build in current UK practice. The zinc coating on galvanised ties can fail within 15–30 years in moderate to severe exposures, leading to the same tie corrosion and failure problem that has affected hundreds of thousands of pre-1980s properties. Stainless steel (A2 or A4 as appropriate) is the correct specification for all new work.

Do I need to change tie spacing for a 150mm cavity?

The standard 2.5/m² frequency (900mm horizontal, 450mm vertical) generally applies regardless of cavity width, provided the tie length is correct for the cavity and the tie is rated for the required load. For very wide cavities (150mm+), consult a structural engineer, as the slenderness of the outer leaf and the bending moment in the tie both increase with cavity width.

What tie should be used in a timber-frame cavity wall?

Timber-frame construction (structural timber inner leaf, masonry outer leaf) uses different tie types fixed through the sheathing board into the structural studs. Standard horizontal flat ties are not used in the same way. Specialist timber-frame wall ties (screw-in or through-stud types) are used instead. The tie manufacturer and the timber frame designer/engineer should specify the appropriate product, fixing detail, and spacing for the specific panel configuration.

Regulations & Standards

• BS EN 845-1 — Specification for ancillary components for masonry: ties, tension straps, hangers and brackets; defines load categories and material requirements for wall ties

• BS EN 1996-1-1 (Eurocode 6) — Design of masonry structures; tie spacing and load design

• BRE Digest 329 — Assessment of damage in low-rise buildings; corrosion zone classification for wall tie material selection

• BRE Good Repair Guide 2 — Diagnosing cavity wall tie corrosion and failure; remedial options

• NHBC Standards — Chapter 6.1 — External masonry walls; tie specification and workmanship standards for new-build

• BRE Digest 329 — Corrosion zone assessment and tie material selection

• Helifix — Remedial wall tie guidance — Remedial tie installation methods and case studies

• Ancon — Wall tie specification and selection — New-build tie range with BS EN 845-1 data

• NHBC Technical Standards — Minimum standards for new-build masonry cavity walls

• Brick Development Association — Technical guidance on cavity wall construction

• grout types — Another cross-reference on material selection

• solder types — Material selection for plumbing and electrical applications