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There are specific criteria to follow when choosing weep technology. According to wiseGeek.com, “A weep screed is a type of building material used along the base of an exterior stucco wall. The screed serves as a vent so that the moisture can escape the stucco wall finish just above the foundation.” It is a device used to terminate the bottom of a cementitious-based thin veneer rainscreen. This device should allow liquid moisture that drains down the back side of a thin veneer rainscreen and on the surface of the weather resistant barrier in the rainscreen drainage plane to freely exit the thin veneer 1.5” to 2” below the bottom of the framed wall system and the top of the stem wall. Section 2512.1.2, Weep Screeds, of the 2012 International Building Code states, “A minimum 0.019-inch (0.5 mm) (No. 26 galvanized sheet gage), corrosion-resistant weep screed or plastic seep screed, with a minimum vertical attachment flange of 3.5 inches (89 mm) shall be provided at or below the foundation plate line on exterior stud walls in accordance with ASTM C 926. The weep screed shall be placed a minimum of 4 inches (102 mm) above the earth or 2 inches (51 mm) above paved areas and shall be of a type that will allow trapped water to drain to the exterior of the building. The weather-resistant barrier shall lap the attachment flange. The exterior lath shall cover and terminate on the attachment flange of the weep screed.” (See P16)
It is critical that the drainage holes/weep holes be numerous and not more than 1 inch (or so) apart and located at the bottom of the weep screed and against the 3.5” back flange to allow for direct contact with the bottom of the rainscreen drainage plane. (See P17, 17A, 17B) This is critical for two reasons: First, the liquid moisture that drains down the rainscreen drainage plane/drainage mat will have an immediate exit point. Second, the cementitious materials used to create the thin veneer will not have access to block them. Dependence on a “shrinkage crack” to handle the amount of moisture that can be potentially drained to the bottom of the wall is inviting moisture-related building envelope failure!
MTI manufactures one of the few weep screeds on the market today that actually weeps.
You can visit our HyperSpecs Library of moisture management details to view detailed drawings and installation animations of L & R Weep ScreedTM used in specific applications. The links below will take you to details that correspond to the four images above. HyperSpecs can also be searched for additional details that may better reflect your specific needs. If you need a custom detail Contact Us!
For complete information on this product visit the L & R Weep Screed product page.
To learn more about effective weeps and weep screeds, download the MTI article "Getting to the Bottom of Moisture Management." This heavily illustrated article points out the necessity of the right type of mositure management at the bottom of walls.