Wall Ties: Types, Spacing and BS EN 845

Summary

Wall ties tie the inner and outer leaves of a cavity wall into a single structural unit. They transfer lateral wind loads from the outer leaf back to the inner leaf, allow each leaf to flex independently without separating, and prevent the outer leaf from acting as a freestanding panel. Get the ties wrong — wrong type, wrong spacing, missed at openings, sloped the wrong way — and the wall is no longer a cavity wall in the structural sense; it is two leaves held up by friction and luck.

The 1981 change to mandatory stainless steel ties (after widespread galvanised-steel failures) and the move to BS EN 845-1 from the older BS 1243:1978 brought the UK in line with European masonry standards. The relevant performance characteristics — declared load capacity, ductility, fire performance, durability classification — are now declared by the manufacturer under the Construction Products Regulation (CPR). The job on site is to specify and install ties whose declared performance matches what the structural engineer (or PD 6697 Table 2 for routine work) has asked for.

For tradespeople this matters in three situations: building new cavity walls, retrofitting ties to existing walls where a survey has found them inadequate or corroded, and tying-in new openings (lintels, padstones, structural reinforcement). The technique is straightforward; the consequences of getting it wrong are not. Tie work is notifiable under Building Regulations Part A, and Building Control will expect to see manufacturer specification, installation record and competency evidence.

Key Facts

• Primary standard — BS EN 845-1:2013 + A1:2016, Specification for ancillary components for masonry, Part 1: Wall ties, tension straps, hangers and brackets
• Design code — PD 6697:2019, Recommendations for the design of masonry structures (replaces BS 5628-3)
• Building Regulations — Approved Document A (Structure); ties are notifiable when used in structural masonry
• Minimum density — 2.5 ties/m² for cavities up to 75mm; rising to 4.9 ties/m² for cavities >150mm at higher exposure
• Standard spacing — 900mm horizontal × 450mm vertical (every 6th brick course) on a staggered pattern
• Perimeter and opening rule — Additional ties within 225mm of any unbonded edge, opening jamb, movement joint or roof edge, at maximum 300mm vertical centres
• Tie length — Embedment of at least 50mm into each leaf, with a 5–15mm gap between the drip and the outer leaf face
• Drip position — The plastic drip ring or twist must sit in the cavity, pointing downward, to shed water away from the inner leaf
• Stainless grade — Minimum 1.4301 (304); use 1.4401 (316) within 1km of the coast or in industrial/polluted areas
• DPC and tie interaction — No ties through a DPC; below-DPC ties (in the foundation/footing zone) are not required for structural reasons
• Movement joints — Use ties with a debonding sleeve over a movement joint so the leaf can move horizontally without restraint
• Insulation retention — When a partial-fill cavity is used, insulation retainer discs clip onto the tie to hold rigid board against the inner leaf
• Helical retrofit ties — For tie replacement, BS EN 845-1 compliant helical resin-fixed stainless ties (e.g. Helifix HeliBar) at typically 4 ties/m² to compensate for unverified existing ties

Quick Reference Table

Detailed Guidance

Selecting the Right Tie

Tie selection follows PD 6697 Table 2 for routine domestic work — the structural engineer's calculations override this for taller buildings, unusual geometry, or where loadings are atypical. The two governing variables are cavity width and the declared load capacity of the tie under wind load.

Vertical twist ties are stiffer than wire butterfly ties and transfer load more positively, which makes them the default for any wall above two storeys and for exposure zones 3–4. Butterfly ties are limited by PD 6697 to lower-rise sheltered work; they remain common in suburban housing but their use is restricted as cavity widths increase. Double-triangle wire ties sit between butterfly and twist ties in stiffness.

For wide cavities (>100mm, increasingly common with deep insulation), check the manufacturer's declared performance for the specific cavity width — a 250mm tie does not perform the same as a 200mm one in the same family, because the unsupported length increases the risk of buckling under wind suction. Some manufacturers publish supplementary tables; others require an engineer's specification.

Spacing and Layout

The standard pattern is 900mm horizontal × 450mm vertical, staggered between alternate courses, giving 2.5 ties/m² (1 ÷ (0.9 × 0.45) = 2.47). For higher density (4.9 ties/m²) drop the horizontal spacing to 450mm at 450mm vertical, or 600mm at 375mm vertical depending on coursing.

Perimeter ties go in at:

• Vertical jambs of openings — within 225mm of the reveal, at maximum 300mm vertical centres
• Unrestrained vertical edges — corners (within 225mm of the return), movement joints, junctions with timber frame
• Top of wall — within 225mm of the wall plate or roof-edge restraint
• Lintel bearing — at each end of every lintel, additional to the standard pattern

These additional ties matter because openings interrupt the normal load-shedding path; a window jamb without close ties is the most common place to find cavity walls separating.

Installation Detail

A tie should slope very slightly downwards from the inner to outer leaf — typically 5–10mm — so that any water tracking along the tie drips into the cavity, not back onto the inner leaf. The drip (the plastic ring on a wire tie, the twist on a strip tie) sits in the cavity, halfway between the leaves where practical, never resting on insulation or against the outer leaf.

The tie bears 50mm into each leaf as a minimum. On the outer leaf this means it is laid into a full mortar bed; do not press a tie into a thin "buttered" joint, and never bend a tie around an obstruction in the inner leaf. If a tie cannot be installed in its planned position because of an obstruction, install a substitute tie within 225mm at the next available coursing.

Insulation retainer discs clip onto the tie before it goes into the inner-leaf bed joint, then the rigid insulation board is pushed onto the tie and the disc is rotated to hold the board against the inner leaf. The disc must hold the board firmly — a board that has slumped 5mm away from the inner leaf creates a thermal bypass that no amount of cavity sealing will recover.

Retrofit and Remedial Tie Installation

When an existing wall fails the survey — corroded original ties, missing ties, or signs of leaf separation — replacement is by helical resin-fixed ties driven through the outer leaf into the inner leaf. The pattern is denser than original (typically 4 ties/m²) on the assumption that some original ties may still be working and the new pattern carries the load on its own.

The full procedure is covered in cavity wall ties; the key spacing rule for retrofit work is that the new tie pattern is laid out independently of the original, on a fresh chalked grid. Locating an old tie position with an electromagnetic detector and then installing a replacement tie 50mm to one side is acceptable; trying to drill through an existing tie is not — it deflects the new tie and risks damaging the outer face.

Common Site Mistakes

1. Ties sloping the wrong way. A tie that slopes from outer to inner leaf channels water onto the inner leaf — the cavity becomes a damp bridge. Check by eye every course and reset any tie that is not bedded with a downward slope into the cavity.
2. Missing ties at openings. The standard 900×450 grid does not provide enough ties around openings; the additional perimeter ties are not optional.
3. Ties dragging insulation. When pushing insulation against the inner leaf, ties not yet held by retainer discs flex outward and the insulation slumps into the cavity. Fit the retainer disc before pushing the board home.
4. Mortar snots on the tie. A blob of mortar on the cavity side of a tie acts as a damp bridge. Knock excess mortar off as you go.
5. Wrong grade in coastal work. Grade 304 in zone 4 will eventually pit and fail; the cost difference to grade 316 is small relative to the cost of retrofit.
6. Using construction adhesive instead of resin for retrofit ties. Resin systems are tested and certified to BS EN 845-1 for tie work; PU adhesive is not, and Building Control will reject the work.

Frequently Asked Questions

How many wall ties do I need for a typical 4 × 2.5m wall panel?

That panel is 10m². At the standard PD 6697 density of 2.5 ties/m², you need 25 ties — but add perimeter and opening ties on top. For a panel containing a single 1.2 × 1.2m window, expect to install roughly 35–40 ties (25 standard plus 10–15 additional around the opening, top edge and jambs).

Can I reuse existing ties when rebuilding a section of outer leaf?

No. Once a tie has been disturbed during demolition of the outer leaf its embedment is compromised and its tested performance no longer applies. Cut the original tie back flush with the inner leaf face and install new ties as if it were a new build. The exception is where the engineer has specifically designed the connection — e.g. a stitch-bonded repair using helical bars — in which case follow the engineer's detail.

What's the difference between a Type 1 and Type 4 tie?

In BS EN 845-1, ties are classified by declared tensile and compressive load capacity. Type 1 (heavy duty, vertical twist) has the highest capacity and is required for taller buildings and exposed sites. Type 4 (light duty, butterfly wire) has the lowest, and is restricted by PD 6697 to lower-rise sheltered work. Most domestic two-storey work in moderate exposure can use Type 2 (double-triangle wire) without an engineer's calculation.

Do I need a tie at every opening jamb?

Yes — within 225mm of the reveal, at maximum 300mm vertical centres, both sides of the opening. This is in addition to the standard 900×450 grid, not instead of it. A common error is to count an opening-jamb tie as one of the grid ties, which leaves both inadequately spaced.

How do I tie new masonry into an existing wall?

Two options: stainless steel masonry connector channels (cast or bolted to the existing wall, with debonded ties engaging the channel) or helical ties driven into the existing structure (typically 6–8mm helical bars in resin). Both are covered by BS EN 845-1 declared performance. For load-bearing junctions the engineer specifies which; for non-load-bearing junctions either is acceptable.

Regulations & Standards

• BS EN 845-1:2013 + A1:2016 — Specification for ancillary components for masonry, Part 1: Wall ties (the product standard)

• PD 6697:2019 — Recommendations for the design of masonry structures, BSI (the design rules)

• Approved Document A — Building Regulations Part A: Structure (notifiable; Building Control inspection required for new structural masonry)

• BS EN 1996-1-1:2005+A1:2012 — Eurocode 6: Design of masonry structures (used by engineers for non-routine work)

• BS 8104:1992 — Code of practice for assessing exposure of walls to wind-driven rain (exposure zone classification)

• BRE Digest SD3 — Cavity wall tie corrosion (retrofit and remediation reference)

• NHBC Standards Chapter 6.1 — Foundation conditions and external masonry (warranty-provider requirements)

• BS EN 845-1 on BSI — Wall tie product standard

• PD 6697:2019 on BSI — Masonry structures design guidance

• Approved Document A — Structure — Building Regulations Part A

• NHBC Standards Chapter 6.1 — External masonry warranty requirements

• cavity wall ties — Remedial tie replacement procedure

• cavity wall tie types — Detailed tie type comparison

• mortar mixes — Mortar specification for cavity work

• expansion joints — Tie selection at movement joints