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Elaborate and expensive precautions are taken in buildings to prevent the entry of even a drop or two of water, because water is an agent of destruction. Water chills the skin, destroys the insulating value of clothing and building fabric, and raises the moisture content of the air in buildings to unhealthy levels. Water is the universal solvent, dissolving many materials used in building interiors and encouraging the staining or corrosion of others. Water is a necessity for all forms of life, including bacteria, molds, mildew, other fungi, plants, and insects. A leaking building is not only uncomfortable and unsanitary, but it's also destined for an early death through corrosion, decay, and insect attack.
A Theory of Watertightness
In order for water to penetrate the enclosure of a building, three conditions are necessary:
1. Water must be present at the surface of the enclosure.
2. There must be an opening in the enclosure through which the water can pass.
3. There must be a force to move the water through the opening.
These conditions are so simple as to be self-evident, yet they constitute a complete basis for the systematic exclusion of water from a building. Unless all three conditions are satisfied, water can't enter. By eliminating any of the three conditions at a given location on the building enclosure, a watertight condition can be ensured.
The Presence of Water
Water is present in and around a building in many guises. Rain and snow impinge directly on the skin of a building and collect on the ground around it, bringing surface runoff and subsurface water into contact with its foundations. Water can be tracked into a building by people or vehicles. Inside a building, atmospheric moisture can condense on cold surfaces and drip onto the floor. Piping, plumbing fixtures, cooking, washing, bathing, and industrial processes may cause leakage or spillage of water. Building materials that are put in place wet, such as concrete, brickwork, tile work, and plaster, release large amounts of water vapor as they dry, frequently causing copious condensate to run from windows and cold-water pipes.
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