The cavity must also not be continuous around the sides of the building as it creates a positive pressure on that face. However, a negative pressure is created on the sides, roof and rear of the building. If the cavity between the two layers is continuous around the corner of the building, air will blow through the cavity to the sides of the building and pressure equilization will not occur. This could force rain into the cavity and water leakage could occur. A similar action will occur if the cavity is open at the top of the wall (Fig. 2). To make the rain screen function, the cavity must be divided into compartments. each of these compartments must be airtight to allow pressure equalization to occur.