Waterproofing is the building envelope that protects the building cosmetically and structurally. Water infiltration can cause major problem to a structure. It will first damage the building cosmetically then structurally. Unfortunately, most of the time it is considered as an inconvenience rather than a serious matter
However it is important to realize that by the time a stain shows up on the interior of your building most likely irreversible damage has been caused to the exterior. Water soaked roof insulation will almost never dry out.
Trapped moisture in insulation can also decay a roof deck and will cause roofs to fail prematurely. Water entering walls will rust steel, discharging angles and carrying beams, which support the structure. Moisture penetrating reinforced concrete structures carry chloride ions, which will rust reinforcing bars causing them to expand in size resulting in spalling of concrete. As one begins to understand the process of water infiltration one begins to understand the importance of keeping a building waterproofed.