The rainscreen wall incorporates two layers seperated by an air space, or cavity. The inner layer of the wall (the air barrier) is airtight, while the outer layer (cladding) is vented to the outside. When the wind blows on the building, a pressure difference is created across the cladding. With a rainscreen wall, a small amount of air enters the cavaity and is trapped by the inner air tight layer, causing the pressure in the cavity to increase until it equals the exterior pressure (Fig. 1). The air trapped in the cavity counteracts the wind blowing on the building and reduces the pressure difference across the cladding of the wall. Therefore, as there is no force to cause the water on the surface of the wall to move inwards, rain penetration is effectively reduced. For the rainscreen to function, the inner layer of the wall must be airtight. If there are leakage openings in the inner layer, the pressure in the cavity will not equalize with the exterior pressure and rain penetartion may occur. However, it is easier to seal this layer than it is to seal the outside of the wall, and the seal will last longer because the inner layer is not exposed to the harsh exterior environment. Any water that does penetrate the outer layer because of gravity forces or capillarity should drain back to the exterior face of the wall. Flashing details in the cavity are thus very important.