Cavity walls are a type of masonry construction in which two separate wall leaves or ‘wythes’ are joined together with mortar but have an empty space (usually about 10 cm or just under 4 inches) between them. The wythes are bonded together by blocks of brick or metal ties for structural strength. The cavity is typically filled with mineral wool insulation during construction. This is a good way to prevent dampness in homes built using this technique.
One of the main advantages of a cavity wall is moisture prevention, as the gap between the wythes stops water from the outer leaf percolating into the inner leaf. They are also able to provide much better thermal insulation than solid masonry walls of the same thickness.
However, the performance of a cavity wall depends on a number of factors. The air space between the wythes must be free of any material that could form a water bridge, and the wythes must be constructed with high-quality masonry units. Furthermore, the weepholes or gaps in the pointing must be kept clear of mortar droppings to ensure that built-up water can drain back through them.
Nevertheless, cavities have been used for a long time and have a good track record of performance under widely varying conditions. They are also considerably cheaper to build than a solid wall of the same thickness, and their insulation properties make them very energy efficient. Considering all of these benefits, cavity walls are an excellent choice for modern housing.