Dynamic wind pressure on the surface of an exposed wall can drive exterior moisture (in the form of rain or irrigation water) into the masonry. Significant forces that influence water movement include wind pressure, gravity, and moisture absorption by the material. In the design of any structure, the presence and movement of water in any of its three forms needs to be considered. This damage may appear in the form of water stains, ravelled mortar joints, spalled surfaces, or efflorescence. For example, in some instances it is possible for the humidity of interior air to cause water damage to the exterior of a structure. During cold weather, below 28 ☏ (-2 ☌), water vapor can accumulate on a cold surface and form frost or increase the quantity of ice within the masonry.Īlthough it is commonly thought that moisture problems stem only from the external environment, this is not always the case. Alternatively, water vapor can lead to condensation inside the cores and on the surfaces of masonry if the dew point temperature is reached. In some extreme cases, water trapped within the masonry may freeze, inducing spalling and cracking of the masonry units or mortar. For example, in the liquid state, water penetrating to the interior of a building may cause considerable damage to its contents. The damage caused to a masonry structure (or its contents) due to the infiltration of moisture can take many forms, depending on the source and the physical state of the water. 3) includes such details.Īlthough flashing is the primary focus of this TEK, it should be understood that the role of vapor retarders, air barriers, and insulation are also important elements to consider for any wall design as the performance of the entire system can be dependent on the design of its individual components. TEK 19-5A Flashing Details for Concrete Masonry Walls (ref. Drawings for flashing details, often the only method of communicating the necessary information between the designer and contractor, should be comprehensive and show sufficient detail for the proper interpretation and installation of flashing systems. Design/build considerations include the selection of the proper type of flashing material, location of the flashing, structural, and installation details. Environmental considerations include such factors as the physical state of moisture present (liquid, solid, or vapor), air movement, and temperature extremes as well as temperature differentials. The type of flashing material to be used is governed by both environmental and design/build considerations. Due to the abundant sources of moisture and the potentially detrimental effects it can have, the choice of flashing material, and the design and construction of flashing details, can often be as key to the performance of a masonry structure as that of the structural system. The primary role of flashing is to intercept the flow of moisture through masonry and direct it to the exterior of the structure.
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February 2023
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