Where 60 and 10 come from
A UK brick is 215 × 102.5 × 65 mm. With a 10 mm joint its face takes up 225 × 75 mm, so 1,000,000 ÷ (225 × 75) = 59.3 bricks per m². A standard block is 440 × 215 mm, or 450 × 225 mm with joints: 1,000,000 ÷ (450 × 225) = 9.9 blocks per m².
Worked example: a cavity wall
A 6 m long, 2.4 m high cavity wall with a 1.2 × 1.2 m window: facing brick outer leaf, 100 mm block inner leaf, 5% waste.
| Step | Working | Result |
|---|---|---|
| Net area | 6 × 2.4 − 1.44 | 12.96 m² |
| Bricks, +5% | 12.96 × 59.26 = 768, × 1.05 | 807 |
| Blocks, +5% | 12.96 × 9.88 = 128, × 1.05 | 135 |
| Wall ties at 2.5 per m², +5% | 12.96 × 2.5 × 1.05 | 35 |
| Mortar | 768 bricks × 0.00053 + 128 blocks × 0.001, +5% | 0.56 m³ |
Bricks are sold in packs of around 400, so this is two packs plus a few loose, and blocks on pallets of around 48 to 72 depending on the block.
UK rules worth knowing
- Cavity wall ties: Approved Document A gives the spacing, typically 900 mm horizontally and 450 mm vertically (about 2.5 per m²), with extra ties within 225 mm of openings and movement joints.
- Blockwork choice (dense, lightweight, aircrete) depends on loading, thermal performance and fire, so follow the specification.
- Movement joints are needed in long runs of clay brickwork, about every 12 m.