How this calculator works
Worked example: a wall 10 m long and 2.4 m high is 24 m², and three openings of 1.2 × 1.2 m (4.32 m²) leave 19.68 m², which at 2.5 ties per m² is 50 ties. Each opening has a tie every 300 mm up both sides: 5 up each side, so 30 more. That is 80 ties, and 84 with 5% extra. For a 100 mm cavity the tie is 225 mm long. A 150 mm cavity needs 275 mm, a 200 mm cavity 325 mm and a 60 mm cavity 200 mm. With no openings the buy is 63 ties.
Wall tie length for each cavity width
The standard tie length, with at least 50 mm into each leaf.
| Cavity width | Tie length |
|---|---|
| 50 to 75 mm | 200 mm |
| 76 to 100 mm | 225 mm |
| 101 to 125 mm | 250 mm |
| 126 to 150 mm | 275 mm |
| 151 to 175 mm | 300 mm |
| 200 mm | 325 mm |
| 250 mm | 375 mm |
| 300 mm | 425 mm |
Tips before you buy
- Count the ties for the main wall at 2.5 per m², and then add the ties around the openings.
- Stagger the ties in alternate courses so that they are not in line.
- Fit the drip in the middle of the tie so that water on it runs off into the cavity.
- Keep the cavity clear of mortar droppings, which let water across to the inner leaf.
- Tall buildings and exposed sites need a different tie design: ask the engineer or the tie maker.
Tools & materials for this project
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Frequently asked questions
How many wall ties do I need per m²?
At least 2.5 ties per m² of cavity wall, with the ties 900 mm apart across the wall and 450 mm apart up it, staggered.
How many ties go around an opening?
A tie at most every 300 mm up each side of the opening, within 225 mm of the edge: 5 up each side for a 1.2 m high opening.
How long should a wall tie be?
It depends on the cavity. A 100 mm cavity takes a 225 mm tie, a 150 mm cavity 275 mm. The tie goes at least 50 mm into each leaf.
How many ties for this wall?
For this wall, 80 ties, or 84 with 5% extra.
Are these the rules for all buildings?
No. They are the usual spacings in Approved Document A for houses. A tall or exposed building, a timber frame and a very wide cavity follow the tie maker and an engineer.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.