Brick and block wall builder

What it works out

This plans a brick or block wall: a single leaf, or a cavity wall with two leaves, wall by wall with its corners, doors and windows. It lays every course, then counts the bricks and blocks with their cuts, the mortar as sand and cement, wall ties, cavity insulation, cavity closers and damp-proof course.

It draws the wall in elevation, plan and 3D, and gives a course plan with the height of each opening. It works out quantities only: lintels and foundations are never sized here, and walls holding back earth aren't covered.

How it works

Each leaf is laid course by course along its own centre line. The height is rounded to whole courses of the unit plus its joint. Stretcher bond starts alternate courses with a half; English and Flemish bond add headers and queen closers. Openings are taken to the nearest course and the units beside them cut to fit.

Whole units and cut pieces are counted, with two cut pieces taken from one unit where they fit. Mortar is the volume of each leaf's face times its thickness, less the units themselves. It's turned into dry sand and cement for your mix, or bags of ready-mixed mortar.

In a cavity wall, ties are counted over the face at the spacing you set, with more beside each opening. Insulation fills the cavity or partly fills it as boards, closers go round openings, and a damp-proof course runs under each leaf.

A worked example

One straight wall 4 m long and 2.4 m high with a window 1.2 m by 1.05 m, built as a cavity wall: an outer leaf of 215 mm × 102.5 mm × 65 mm units and an inner leaf of 440 mm × 100 mm × 215 mm units, with a 100 mm cavity.

1. Outer leaf: units of 215 × 102.5 × 65 mm with 10 mm joints, stretcher bond, 102.5 mm thick
2. Wall 1, outer leaf: 4 m along its centre line, 32 courses at 75 mm = 2.4 m high, 8.34 m² of face after openings
3. Outer leaf: 453 whole bricks, 76 cut pieces from 47: 500 in all
4. That's 60 bricks per m² of face (8.34 m²)
5. 500 bricks + 10% waste = 550
6. Mortar in the outer leaf: 8.34 m² of face × 102.5 mm, less the units' own 0.709 m³ = 0.146 m³, about 0.0175 m³ per m²
7. Inner leaf: units of 440 × 100 × 215 mm with 10 mm joints, stretcher bond, 100 mm thick
8. Wall 1, inner leaf: 4 m along its centre line, 11 courses at 225 mm = 2.48 m high, 8.55 m² of face after openings
9. Inner leaf: 71 whole blocks, 26 cut pieces from 15: 86 in all
10. That's 10.1 blocks per m² of face (8.55 m²)
11. 86 blocks + 10% waste = 95
12. Mortar in the inner leaf: 8.55 m² of face × 100 mm, less the units' own 0.8 m³ = 0.055 m³, about 0.0065 m³ per m²
13. Mortar: 0.202 m³ + 10% waste = 0.222 m³
14. Dry materials take up about 1.25 times the mortar: 0.277 m³, 1 part cement to 4 parts sand
15. Cement: 0.055 m³ × 1,440 kg/m³ = 79.82 kg: 4 bags of 25 kg
16. Sand: 0.222 m³ × 1,600 kg/m³ = 354.77 kg: 1 bulk bag of 850 kg
17. Ties every 900 mm along and 450 mm up, staggered, 2.47 per m²: 8.34 m² of wall takes 21; 8 more beside openings, every 300 mm up each side within 225 mm of the reveal; 32 with waste, about 1 box of 250
18. Choose the ties' type and length from their maker's table for a 100 mm cavity and the leaves they join.
19. Full-fill batts: 8.34 m² of cavity ÷ 0.55 m² each = 17 of 100 mm, filling the cavity
20. Cavity closers up both sides of 1 opening and under each window: 3.3 m, 3.63 m with waste
21. DPC 112.5 mm wide under 4 m of leaf, 4.4 m with waste, in a bed joint at least 150 mm above the ground
22. DPC 100 mm wide under 4 m of leaf, 4.4 m with waste, in a bed joint at least 150 mm above the ground
23. Openings are taken to the nearest whole course, and the units at their sides are cut to the reveal.
24. Lengths measured on the outside face. Each leaf runs along its own centre line, shorter or longer round corners, and is laid from its start as if stopped at both ends: where the bond turns a corner a few cuts change.
25. Every opening needs a lintel over it. None is sized here: its type and size come from the lintel maker's tables or a structural engineer.
26. The wall stands on a foundation, which isn't worked out here: its size and depth are for building control or an engineer.

Common mistakes

• Counting bricks per square metre and stopping there. Openings, corners and cut pieces change the count. Laying each course shows where the cuts really are.
• Forgetting the lintels. Every opening needs one, and in a cavity wall it carries both leaves with a cavity tray. Its type and size come from the maker's tables or an engineer.
• Building a tall freestanding wall without advice. How high a wall can safely stand depends on its thickness, piers, exposure and ground. A tall one needs a professional's design.
• Mixing too much mortar. Mortar stiffens within a couple of hours. Mix in batches you can lay before it goes off, and never add water to revive it.

Questions people ask