Cavity Wall Ties: Types, Spacing & Replacement

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).¹ 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 galvanised or stainless wire bent into a butterfly or double-triangle profile, with a twist or kink at mid-length that acts as a drip. Butterfly ties are light and flexible; double-triangle ties are stiffer. Galvanised wire ties were widely used in older cavity-walled houses, and newer light-duty ties are now sold as replacements for the butterfly.²

Strip ties (fishtail): Flat metal strip ties with split fishtail ends for grip in the mortar and a drip at mid-length. Heavy galvanised mild steel strip ties are common in older houses, and because they are bulky their rust can lift the brickwork.³

Vertical twist ties: A heavy strip tie with a 90° twist at mid-length. The twist encourages water to drip off rather than tracking along the tie. It is a stiff, heavy-duty pattern; houses more often use lighter general-purpose or light-duty ties.

Modern ties are graded by performance rather than shape: masonry-to-masonry ties are classified as Types 1 to 4 under PD 6697 by strength, function and use.⁴ Type 4 light-duty ties are intended for box-form houses up to 10 m high on flat urban sites, while Type 1 heavy-duty ties suit buildings of any height.⁴

Remedial ties: Stainless steel ties designed to be installed through the face of existing masonry. Remedial wall ties generally fall into three main groups: mechanical, resin-bonded and driven.⁵ They are recessed below the face of the brickwork and are barely visible once the holes are made good.

By Material and Corrosion Resistance

Approved Document A has specified stainless steel cavity wall ties for all houses regardless of location since its 2004 edition, following the widespread failure of galvanised ties built into housing before 1981.⁶ Paragraph 2C19 calls for wall ties to BS EN 845-1 in austenitic stainless steel, so galvanised ties are not an option for a new house built to that guidance.⁶

Tie Spacing and Embedment

Cavity wall tie spacing is defined in Approved Document A (paragraph 2C8), in PD 6697 (recommendations for the design of masonry structures to Eurocode 6) and in NHBC Standards Chapter 6.1 for domestic work:⁶

Standard spacing (cavities at least 50 mm wide):

• 900 mm horizontal centres (along the bed joint)⁶
• 450 mm vertical centres (every sixth course of standard brick)
• This gives 2.5 ties per m² of wall area⁷

Additional ties required at:

• Openings: Extra ties up the reveal of a window or door at 300 mm vertical centres, set no more than 225 mm from the edge of the opening⁶
• Movement joints: extra ties are also needed within 225 mm of vertical movement joints; where a tie spans the joint it needs a slip sleeve or debonded section so the joint can still move⁷
• Roof verges: the same extra ties are needed within 225 mm of roof verges, such as the sloping top of a gable wall⁷

Embedment depth: The absolute minimum is 50 mm into each leaf of masonry, but the figure to design to is 62.5 mm, which is what leaves room for the tie to sit correctly if the cavity or the leaf thickness runs off nominal.⁷ The tie should be centred vertically within the bed joint.

Drip point: Ties have a drip (a twist, kink or bend) that should sit at the middle of the cavity, pointing downwards, so moisture cannot track across to the inner leaf. This requirement is often overlooked on site, check during inspection.

Approved Document A, Table 5, gives the tie length to use for each band of nominal cavity width.⁶

For cavities wider than 175 mm, Table 5 takes the nominal cavity width plus 125 mm and rounds to the nearest stock length; ties that need more than 50 mm embedment must be longer still.⁶

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 1981, before stainless steel became the standard.³ Two corrosion mechanisms are involved:

1. 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. Thin wire ties can corrode through without cracking anything, so the absence of cracks does not prove the ties are sound.⁵

2. Expansive rust jacking, the rust can build up to around four times the thickness of the original steel.³ 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 (typically every five to seven courses)³
• 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 small drilled hole into the cavity) to inspect ties visually, supplemented by a metal detector survey to map tie positions and a pull tester to check how well ties are anchored.³ Site testing of post-installed fixings in masonry is covered by BS 8539 and the Construction Fixings Association’s site-testing guidance; the old BS 5080-1 test method was withdrawn in 2018.⁸⁹ 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 fixing a stainless steel tie into both leaves, mechanically, with resin, or by driving it in. Old ties that are lifting the brickwork, typically mild steel strip (fishtail) ties, are removed or isolated from the mortar; lighter wire ties can often be left in place.³ The new ties are set out clear of the old ones, transferring load through sound masonry.

Horizontal cracks are repointed after tie installation, and wider cracks may need stitching or other repair.

Process per tie:

1. Mark tie positions from the survey (or at 900 × 450 mm grid if systematic replacement)
2. Drill through the outer leaf into the inner leaf at bed joint level; hole sizes vary by system, from a pilot hole of around 6 mm for driven ties to 10 mm for resin-bonded ties¹⁰
3. For resin-bonded ties, inject a two-part resin into the hole
4. Insert or drive the stainless steel tie until its outer end sits below the face of the brickwork¹¹
5. Repoint drill holes with matching mortar
6. Repoint horizontal cracks if present

2026 costs (UK, VAT excluded):

Supply prices are small next to the labour: a remedial supplier lists boxes of 100 helical ties at £113.45 to £177.03 including VAT and delivery, depending on length.¹² For new build, Selco lists a pack of 250 light-duty Type 4 stainless ties at £37.05 excluding VAT, about 15p a tie.¹³

Key Standards

• BS EN 845-1:2013+A1:2016, Specification for ancillary components for masonry: wall ties, tension straps, hangers and brackets
• PD 6697:2019, Recommendations for the design of masonry structures to BS EN 1996-1-1 and BS EN 1996-2 (tie types, lengths, embedment and density)¹⁴
• BS 8539:2012+A1:2021, Code of practice for the selection and installation of post-installed anchors in concrete and masonry, including site testing (the old BS 5080-1:1993 tensile test method was withdrawn in 2018)¹⁵
• BRE Digest 401 (1995), Replacing wall ties¹⁶
• BRE Digest 329 (2000), Installing wall ties in existing construction¹⁷
• NHBC Standards Chapter 6.1, External masonry walls, tie specification for warranty compliance
• Building Regulations Approved Document A, Structural performance of masonry walls

Partial vs full replacement

Where ties have failed, specialists normally allow for re-tying the whole property, on the assumption that the same corrosion will develop throughout; limiting the work to one elevation should be a decision backed by a survey.³ A structural engineer’s report is recommended before agreeing the scope, particularly if bowing is visible.

The rules in this note are those that apply in England. Scotland, Wales and Northern Ireland have their own building standards and permitted development rights.