The Leak Triangle

For leaks to occur, three things are required: water, a hole or path through the cladding, and a force to move the water through the hole. Take away any one of these three elements and there will be no leak. Obviously, if there is no water or path, there will be no leak.

Less obvious is the role of 'Force'. If no force exists, then even if water and a hole are present, there will not be a leak.

The five forces that move water through a hole are gravity, kinetic energy, surface tension, capillary movement and pressure difference. We can't eliminate the forces of nature, but we can work to deal with their effects.

Gravity is overcome with flashing and by allowing drainage to the exterior at the bottom of a cavity. Putting a cover over an opening controls kinetic energy. For example, we shut the window when it starts to rain. Putting a drip on ledges controls surface tension and capillary movement is stopped by adding a chamber - a capillary break. Pressure difference is caused largely by wind pressure and is controlled by adding an air barrier to the wall.

The Leak Triangle: Remove any element and there will not be a leak.