Cavity wall
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Cavity walls are two-part masonry that include a cavity, a hollow space.
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[edit] Introduction
The masonry sections of a cavity wall can be brickwork, blockwork or similar and don't have to be the same on each side and, while the cavity is initially empty, it can be filled with insulation by various methods. The benefits of cavity walls are widely recognised and they are the most commonly used form of external wall in the United Kingdom due to flexibility, cost effectiveness and potential for insulation.
[edit] Insulation
Even with the cavity left unfilled, the air trapped is a good insulator and dramatically reduces thermal energy lost through the walls. This is because, firstly, air is a poor conductor of heat and it must first be conducted through it onto the outer walls before being convected, as well as that the air pockets can hold heat for a longer time than the bricks, and therefore thermal energy does not move into the hotter environment (the cavity), but instead into colder regions.
With environmental conditions becoming more of an issue, people now take much more interest in reducing energy wastage and cavity wall insulation is a cost effective way to reduce the amount of heat lost from convection off walls. As well as being more environmentally friendly, it can reduce heating costs as more of the heat is used effectively and it is often used as a first step, due to it's low payback time and smaller initial installation costs.
[edit] Specification
A cavity wall is often constructed with a half brick thick outer skin (102.5mm) and a dense concrete blockwork inner skin (100mm). The cavity size can range from 50mm to 100mm and it 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.
[edit] History
Although cavity walls did not become common until the 20th century, they were introduced into the United Kingdom during the 19th century. In some early examples stones were used to tie the two leaves of the cavity wall together [1].
