The cavity wall was introduced into buildings because it is the greatest of all damp precautions, water cannot travel across a void. Most masonry is pourus to some degree, and sooner or later, especially with weak, or incorrectly constructed joints, that masonry will let in water. Without a barrier of some kind, there is a chance that water will work its way indoors, however thick the wall. By inserting a cavity, that scenario is impossible. For a number of reasons that we will explain below, the cavity has to be bridged. That is the two leaves, or skins, of the wall have to be connected. We will start of the bottom of the diagram and explain. At the bottom of every cavity is a foundation of some kind, this will be dealt with in another project which will include a ground floor slab construction.

We have a range of solutions for various applications and wall types.

The first thing we see as we go up the cavity is a wall tie, this is necessary to "tie" the two halves of the wall together and stop one moving independently of the other. An important function, but from a damp point of view, sometimes a dangerous one. If the wall tie, which is built into the joints of the masonry, is placed so that it slopes down toward the inner skin of the building, water can run down it and soak into the inside wall. To counteract this, firstly it is important they are installed "on the level" or even sloping toward the outside of the building. Secondly, the wall ties themselves have a kink, twist or tail, which allows water to form on this part of the tie and, given that water cannot run uphill, drip off the lowest point.