![]() ![]() Mechanical and stack effect pressures are generally considered static or constant pressures that impact building envelope moisture infiltration and exfiltration. Pressure differences across the building envelope can result from wind, mechanical systems and stack effect. A simple drip edge metal detail is a good example of a capillary break. ![]() Understanding how certain wall systems react to capillary forces allows for detailing capillary breaks or small gaps within the wall system. For example, grade-level masonry walls can wick surface ground water vertically at a surprising rate depending on the porosity and openings of the masonry material. Capillary forces can defy gravity and can generate deep moisture saturation into building envelope systems. Using gravity to control rainwater by means of weep and flashing systems is fairly well understood, but the importance of well-defined clear path drainage, vertical to horizontal plane changes, end dams, ponding water and continuous water tight membrane detailing that these systems are so critically dependent upon is often neglected.Ĭapillary action – the movement of a liquid along the surface of a solid caused by the attraction of molecules of the liquid to the molecules of the solid – varies greatly within façade systems depending on the porosity of the materials within the wall and the openings that allow a path for water movement inward. The force of gravity can be both a friend and a foe when it comes to managing rainwater. Understanding how these forces impact rainwater penetration is critical in the design of building envelope water management. These forces can come alone or in pairs or all at one time during a windy rainstorm. The most significant forces that drive rain into buildings are gravity, capillary action and wind pressure differences. Water and moisture management strategies must consider the forces that drive water into the building envelope and the building envelope system components required to combat and regulate these forces. Dependence on face-sealed exterior wall systems to control rain-water penetration can have devastating building performance results. and a force to drive the water through the opening.įar too often building design professionals and contractors choose to rely on controlling rainwater penetration by sealing building envelope openings.an opening or path for the water to follow.Three conditions are required to move water through the building envelope: While authoritative data is not available, it is estimated that up to 80% of construction related lawsuits are related to the building envelope. Uncontrolled water and moisture ingress are two of the most common enemies of the building envelopes, threatening structural integrity and performance. Overcoming two common threats to building performance & structural integrity ![]()
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