6.1.18 Wall ties, bed joint reinforcements and windposts
Wall ties and bed joint reinforcements and windposts of the correct type shall be installed where required, and be suitable for their intended use and location. Issues to be taken into account include:
- position
- ties for partial fill insulation
- cavity widths of over 100mm.
Wall ties should:
- be in accordance with BS EN 845-1 or Technical Requirement R3
- be of the type as specified in the design
- be long enough to be embedded a minimum of 50mm into each leaf
- be stainless steel or non-ferrous
- be spaced above and below the DPC in accordance with Table 9
- be of the type or classification that is appropriate for the end use (including cavity width) and geographical location
- be specified to accommodate movement where required by the design
- be used in accordance with manufacturers recommendations.
Bed joint reinforcements should:
- be in accordance with BS EN 845-3 or Technical Requirement R3
- be of the type as specified in the design
- be sufficiently wide so that minimum cover of 20mm is provided from the external face of masonry
- be stainless steel or non-ferrous
- have a minimum lap length of 225mm and laps between lengths should always be staggered
- be used strictly in accordance with manufacturers recommendations.
Windposts should:
- be designed by an engineer in accordance with Technical Requirement R5
- comply with Cl. 5.12 and Table 2 of PD 6697:2019 'Recommendations for the design of masonry structures to BS EN 1996-1-1 and BS EN 1996-2'
- be austenitic stainless steel (chrome nickel alloys) or austenitic stainless steel (molybdenum chrome nickel alloys) where connected to or embedded in the external leaf of an external cavity wall
- be austenitic stainless steel (molybdenum chrome nickel alloys) where used in aggressive environments, eg coastal locations.
Position#
Table 9: Spacing on wall ties
| Maximum horizontal spacing (mm) | Maximum vertical spacing (mm) | |
|---|---|---|
| General wall area | 900 | 450 |
| Jamb openings, movement joints, etc | Within 225 of opening | Not more than 300(1) |
| Top of gable walls | 225 (parallel to the top of the wall) | Not more than 300(2) |
| Top and bottom of openings | 450 | N/A |
Notes
1. Vertical spacing and number of ties may need adjusting to produce equivalent number of ties when using insulation boards.
2. Vertical spacing and number of ties may need adjusting to produce equivalent number of ties when using studded or spandrel panels.
Water should be prevented from crossing the cavity. Care should be taken to avoid:
- ties sloping down to the inner leaf
- drips being off-centre
- ties having mortar droppings on them.
Cavity walls should be coursed so that the wall tie is level or slopes outwards.
Figure 38: Wall tie locations
Figure 39: Wall tie embedment
Figure 40: Wall tie to partial fill insulation
Wall ties should be:
- built in and not pushed into joints
- be of sufficient length to achieve a minimum 50mm embedment into each leaf of masonry, allowing for normal tolerances in cavity width
- positioned so that the drip is centred in the clear cavity and faces downwards.
Ties for partial fill insulation#
Where partial cavity fill insulation is being used, it should be held against the inner leaf by retaining devices, which may be clipped to the wall ties. Retaining devices should be:
- compatible with the wall ties
- used in accordance with Technical Requirement R3.
Where 1,200mm boards are used with partial fill cavities, the wall ties should:
- be spaced closer to provide adequate support and restraint
- be spaced at 600mm centres in rows ie, not staggered.
Cavity widths of over 100mm#
Where cavity to masonry walls is to be between 100-150mm, wall tie spacing in Table 10 above may still be used in dwelling of up to three storeys high in sheltered and moderate exposure locations, provided they are of the right length with 50mm minimum embedment in the masonry.
Where dwellings are exposed to severe and very severe winds including on exposed and elevated locations of over 150m above sea level as well as coastal locations, site specific assessment of wall tie requirements should be undertaken. The wall tie spacing in Table 9 above may still be acceptable, if used in conjunction with stiffer wall tie types – eg Type 1 or 2 in accordance with PD 6697.
Last updated: 27th February 2024