# construction.brick-count

Bricks and mortar for a wall of UK standard bricks, with doors and windows
subtracted.

## The brick

A UK metric brick is 215 × 102.5 × 65 mm (work size). Laid with 10 mm joints
it occupies 225 × 75 mm of wall face (the coordinating size), so one square
metre of a half-brick (single-skin) wall takes 1,000,000 / 16,875 = 59.26
bricks, which the trade calls "60 a metre". A one-brick wall (two skins) is
twice that, 118.5, so 119 for a square metre rather than the 120 that doubling
the rounded figure gives.

## How it is worked out

1. Wall and openings, given in metres, are taken to the nearest millimetre;
   the net face area is the wall less the openings, in whole mm².
2. **Bricks** = net area × skins × (1 + wastage) ÷ 16,875 mm², rounded up.
3. **Mortar** is the joint volume the geometry implies, not a rule of thumb:
   per skin, the joints are (16,875 − 215 × 65) / 16,875 of the face, 102.5 mm
   deep, which is 17.6 litres per m²; each collar joint between skins adds a
   10 mm layer, 10 litres per m². Rounded up to a whole litre, then the
   wastage added and rounded up to a litre again.

All arithmetic is in integers after step 1, so it does not suffer from
floating-point ceilings.

## What it does not count

Frogs and perforations (a frog-up brick takes more mortar; add it to the
wastage), cavity walls built with a block inner leaf (count the brick skin
here, blocks separately), ties, lintels, piers and returns, and the bond:
English and Flemish bond one-brick walls use the same number of bricks per m²
as two stretcher skins, but headers change how many facing bricks you need.

Limits: length up to 1000 m, height up to 100 m, 1 to 4 skins, wastage 0 to
10,000 basis points. Openings larger than the wall are an error; openings
equal to it leave nothing to build.

## Sources

- BS EN 771-1 (clay masonry units) and the UK standard format of
  215 × 102.5 × 65 mm with a 225 × 112.5 × 75 mm coordinating size; see
  "Brick sizes", Designing Buildings Wiki,
  https://www.designingbuildings.co.uk/wiki/Brick_sizes
- The 60 bricks per m² single-skin rule as used in the UK trade, e.g.
  https://www.imperialbricks.co.uk/guidance/bricks-per-m2-guide/