Water Tight Walls, What are water tight walls
Water tight walls speaks to what are water tight walls, why use water tight walls and types of water tight walls.
These are conceptual approaches to water tightness in exterior walls. In detailing the exterior wall for water resistance, we work from an accepted theoretical base as below stated.
In order for water to penetrate a wall three conditions must be available at the same time.
There must be water present at the outer face of the wall.
There must be an opening through which water can pass.
There must be a force to move the water through the opening.
If any one of these conditions is not satisfied, the wall will not leak and this suggests three conceptual approaches to making a wall watertight.
We can try to keep water completely away from the wall. A very broad roof overhang can keep a one or two story wall dry under most conditions. When designing the exterior wall of a taller building, however, we must either shelter each opening with its own small roof, usually not a realistic option or else assume that the wall will get wet.
We can try to eliminate the openings in a wall by building very carefully, sealing every seam in the wall with membranes, sealants or gaskets, attempting to eliminate every hole and crack. This approach which is called “the barrier wall approach” works fairly well if well done but it has inherent problems. In a wall made up of sealant jointed components, the joints are unlikely to be perfect.
If a surface is a bit damp, dirty or oily, sealant may not stick to it. If the worker applying the sealant is insufficiently skilled or has to reach a bit too far to finish a joint, he or she may fail to fill the joint completely. Even if the joints are all made perfectly, building movement can tear the sealant or pull it loose. Because in this approach, the sealant is on the outside of the building, it is exposed to the full destructive forces of sun, wind, water and ice and may fail prematurely from weathering.
Whatever the cause of sealant failure, because the sealant joint is on the outside face of the wall, it is difficult to reach for inspection and repair. Thus, in practice, the barrier wall approach proves unreliable.
In response to these problems, exterior wall designers often employ a strategy of internal drainage or secondary defense, which accepts the uncertainties of external sealant joints by providing internal drainage channels within the wall to carry away any leakage or condensate and backup sealant joints to the inside of the drainage channels.
The ordinary masonry cavity wall facing exemplifies this strategy. The cavity flashings and weep holes constitute an internal drainage system for any moisture that finds its way through the facing bricks. Internal drainage systems are an important component of every metal and glass curtain wall system on the market.
We can try to eliminate or neutralize all the forces that can move water through the wall. These forces are gravity, momentum, surface tension, capillary action and air currents.
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