CORRECT PLACEMENT OF CAVITY WALL TIES
Installation of cavity wall ties.
In this Bitesize CPD we will be looking at the correct placement of cavity wall ties.
Incorrect installation of wall ties has returned as a major issue for FCM’s Clerks of Works during their site inspections. Incorrect sizes, not enough ties, wrong placement in main walls and lack of ties around openings are becoming more common as the lack of apprenticed and experienced bricklayers becomes more common.
Incorrectly spaced wall ties causing expensive and time consuming take down and re-build.
- Cavity wall ties should be stainless steel.
- The maximum horizontal spacing of ties is 900mm and the maximum vertical spacing is 450mm. Ties should be staggered every 6 courses to form a diamond shape.
- Each tie must be set a minimum of 50mm into each masonry leaf.
- Ties should be laid with a slight outward (towards the outer leaf) fall to prevent water tracking back to the inner leaf and causing damp spots.
- Tie patterns change around openings such as doors, windows and movement joints. Vertical ties should be at a maximum of 300mm but are usually set at 225mm to coincide with block sizes. Ties must be within 225mm of the opening.
- Cavity wall insulation usually has a height dimension of 450mm to coincide with wall tie spacing.
- Only insulation retaining clips designed for the used wall tie should be used to ensure correct fixing.
- Insulation should be carefully cut and clipped at openings to avoud holes and cold bridging.
Ties over 225mm from opening.
Wall ties must be embedded at the courses of brick and blockwork are laid and not pushed in after as they will not be held securely or be embedded by the minimum of 50mm
Ties pushed in after wall built – not embedded 50mm or securely held.
Particular care should be made in inspecting vertical tolerances in the brickwork and blockwork as if either drifts from plumb the wall ties will not be embedded into the wall leaves at a minimum of 50mm.
Outer wall not plumb causing cavity spread. Wall ties did not even reach the outer leaf.
Fox Curtis Murray are a building consultancy specialising in providing Clerks of Works services and Quality Control inspections.
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