Specification
A cavity wall is often flipped with a "half brick" thick outer skin and a dense concrete blockwork inner skin (100 mm). The "half brick" in bricklaying parlance actually refers to wall made with bricks laid end to end which just as a normal single-skinned brick wall would be — the "half" in reference to normal thickness which usually equates to "half the length" of the brick. For example, a brick might be 203 mm (8.0 in) long and 92 mm (3.6 in) wide which results in a single-skinned wall as thick as the brick is wide (92 mm in this example) and a double-skinned (no cavity) wall as wide as the brick is long (203 mm). The single-skinned wall is therefore roughly half the thickness of the double-skinned wall, but only because most bricks are roughly twice as long as they are wide.
It is common for external brickwork to be exposed in order to create a visually appealing facade, and for the inner skin (often constructed of cheaper "plaster bricks" or cement blocks) to be plastered over, leaving no visible blockwork. Blockwork can also be used on both sides, and the external skin is either rendered or clad in another material.
The cavity may be partially or completely filled with thermal insulation from the damp-proof course upwards. The two leaves are connected by wall ties to spread lateral loads. Cavity sizes have to adhere to a certain minimum to prevent water penetration and typically are at least 50 mm to 100 mm. Sizes are increasing rapidly to accommodate super-insulating wall specifications, but the larger the cavity the more interior floor area is sacrificed.
Read more about this topic: Cavity Wall