Cavity wall ties are the structural connectors between the outer (usually brick) leaf and the inner leaf of a cavity wall. Without them the outer leaf behaves as a free-standing panel and is vulnerable to wind pressure, while the inner leaf can bow under eccentric floor and roof loads. Despite their critical role, wall ties are rarely thought about until they fail — at which point horizontal cracking in the bed joints or bulging brickwork signals a problem that can cost thousands to remedy.
This guide covers tie types, the correct specification and spacing for new build, and the recognition, investigation and cost of remedial tie replacement.
Types of Wall Tie
Wall ties must comply with BS EN 845-1:2013+A1:2016 (specification for ancillary components for masonry). The type designation refers to their form factor, but the key specification variables are material/coating (controlling corrosion resistance) and configuration (controlling movement accommodation).
By Form Factor
Wire ties (butterfly and double-triangle): Made from plain galvanised or stainless wire bent into a butterfly or double-triangle profile. Cheap and fast to lay but the flat form provides little resistance to differential movement and offers no drip-point in the centre. These were standard in UK housing from roughly 1900–1980.
Fishplate ties (double-ended flat plate): A flat stamped metal plate, wider than wire ties, with an upstand drip in the centre. Good wind-load transfer, widely used in modern domestic construction. The standard product for most new-build work.
Vertical twist ties: A pressed stainless steel tie with a 90° twist at mid-length. The twist encourages water to drip off rather than tracking along the tie. This is now the most common pattern in UK domestic new build.
Remedial (resin-fixed) ties: Helical stainless steel rods (typically 6–8 mm diameter, 160–250 mm long) designed to be drilled into existing masonry and fixed with resin-injection anchors. Used exclusively for tie replacement — they create no line of weakness and are invisible externally after installation.
By Material and Corrosion Resistance
| Material | Specification | Use Case |
|---|---|---|
| Austenitic stainless steel (A2 or A4) | BS EN ISO 3506 | Standard for all new-build UK cavities ≥ 50 mm |
| Hot-dip galvanised steel (HDG) | BS EN ISO 1461, min. 940 g/m² zinc | Cavities ≤ 50 mm in moderate exposure (not recommended for new build) |
| Copper/brass alloys | Niche conservation | Historic masonry — compatibility with lime mortars |
| Stainless steel helical (remedial) | BS 5080 pull-out test required | Cavity tie replacement, injected resin anchor |
Post-2002 practice in the UK requires stainless steel ties for all new cavity walls following the widespread failure of HDG ties built into housing between 1920 and 1980. Specifying HDG ties in new build is now only acceptable in very limited circumstances and is generally avoided.
Tie Spacing and Embedment
Cavity wall tie spacing is defined in PD 6697:2010 (recommendations for the design of masonry structures to Eurocode 6) and in NHBC Standards Chapter 6.1 for domestic work:
Standard spacing (walls up to 12 m high, cavity 50–100 mm):
- 900 mm horizontal centres (along the bed joint)
- 450 mm vertical centres (every sixth course of standard brick)
- This gives 2.5 ties per m² of wall area
Additional ties required at:
- Openings: Extra ties within 150 mm of a window or door reveal, at 300 mm vertical centres up the reveal
- Movement joints: Ties designed to allow differential horizontal movement — use ties with a slip sleeve or debonded section at the joint
- Gable walls and parapets: Increase to 4 ties/m² in exposure zone 3 or 4 (as defined by BRE Digest 438)
Embedment depth: Minimum 50 mm into each leaf of masonry; for 50 mm embedment the mortar joint must be at least 10 mm, meaning a minimum 12 mm joint where the tie sits. The tie should be centred vertically within the bed joint.
Drip point: Wire ties and fishplate ties must have a downward drip or twist at the mid-point of the cavity to prevent moisture tracking across to the inner leaf. This requirement is often overlooked on site — check during inspection.
| Cavity Width (mm) | Minimum Tie Length (mm) | Standard Tie Length (mm) |
|---|---|---|
| 50 | 150 | 175 |
| 75 | 200 | 225 |
| 100 | 250 | 275 |
| 125 | 300 | 325 |
| 150 | 350 | 375 |
Wall Tie Failure and Corrosion
The majority of wall tie failures in existing UK housing involve galvanised mild steel ties installed between approximately 1920 and 1983, before stainless steel became the standard. Two corrosion mechanisms are involved:
-
Sacrificial zinc coating depleted — once the zinc is exhausted, the steel core corrodes and expands. The expansion exerts pressure on the bed joint, creating horizontal cracking at regular vertical intervals (every 450 mm) — the diagnostic signature of tie corrosion.
-
Expansive rust jacking — the rust occupies roughly 7× the volume of the original steel. It literally lifts and splits the brick courses, causing horizontal cracks and, in severe cases, wall bulging (the outer leaf leans outward or inward away from the inner leaf).
Signs of tie failure to look for:
- Horizontal cracks in mortar bed joints at consistent vertical spacings (every 3–6 courses)
- Cracks running across the full width of an exposed brick panel
- Outward bowing or bulging of the outer leaf
- Rust staining visible at the mortar joint
Investigation: A specialist wall tie surveyor uses a borescope (small camera pushed through a 10 mm drilled hole into the cavity) to inspect ties visually, supplemented by a metal detector survey to map tie positions and a pull-out test rig (to BS 5080 Part 1) to test residual anchorage strength. Typical survey cost: £300–£600 for a semi-detached house, more if scaffolding is needed.
Remedial Tie Replacement
Remedial wall ties are installed by drilling through the outer leaf and mortar-injecting a stainless helical rod. The old corroded ties are usually left in place (removing them would require cutting out and replacing every affected course of brickwork, which is prohibitively expensive). Instead, the helical tie is fixed either side of the old tie, transferring load to sound masonry.
Horizontal cracks are repointed after tie installation, and any severely corroded original ties that have fully parted may require a mortar injection to re-bond the leaf to the inner skin.
Process per tie:
- Mark tie positions from the survey (or at 900 × 450 mm grid if systematic replacement)
- Drill 8–10 mm hole through outer leaf at bed joint level
- Inject two-part polyester or epoxy resin anchor to the inner leaf
- Insert stainless helical rod; tap home while resin cures
- Repoint drill holes with matching mortar
- Repoint horizontal cracks if present
2026 costs (UK, VAT excluded):
| Item | Unit Cost | Notes |
|---|---|---|
| Remedial tie (supplied) | £1.50–£4.00 | Helical rod 250–300 mm, stainless A4 |
| Tie installation (labour + material) | £30–£60/tie | Includes drilling, resin, pointing |
| Full house remedial programme | £3,000–£8,000 | Typical 3-bed semi, access by cherry-picker or scaffold |
| Scaffold/cherry-picker hire | £800–£2,500 | Per week; often the dominant cost |
| New-build ties (supply-only) | £0.20–£0.80 | Stainless vertical twist or fishplate |
Key Standards
- BS EN 845-1:2013+A1:2016 — Specification for ancillary components for masonry: wall ties, tension straps, hangers and brackets
- PD 6697:2010 — Recommendations for the design of masonry structures to Eurocode 6 (tie spacing tables)
- BS 5080-1:1993 — Structural fixings in concrete and masonry: pull-out tests
- BRE Digest 401 (1995) — Replacing wall ties
- BRE Digest 329 (1988) — Installing wall ties in existing construction
- NHBC Standards Chapter 6.1 — External masonry walls — tie specification for warranty compliance
- Building Regulations Approved Document A — Structural performance of masonry walls
[!info] Partial vs full replacement If fewer than 25 % of ties in a wall panel have failed, partial replacement (installing new ties at 450 × 900 grid, leaving failed ties) is acceptable. Above 25 % failure rate, full remedial re-tying is normally specified. A structural engineer’s report is recommended before agreeing the scope, particularly if bowing is visible.
