Masonry Design: Not-Quite-Through-Wall Flashing

Through-wall flashing is a common water management feature of masonry cavity wall and veneer construction. It is most effective if its outer edge is beyond the outer face of the wall and is turned down to form a drip edge and help water fall away from the joint under the flashing. It can be ineffective and result in leaks into a building if the outer edge of the flashing is concealed within the wall. In at least one case, a leak was attributed to flashing that stopped above the core holes of extruded brick. The design relied on the through-wall flashing to protect the building interior, but water which was intended to be conveyed out of the wall by the through-wall flashing was instead allowed to re-enter the wall and subsequently find its way to the building interior. Apparently, someone did not want to see the edge of the flashing coming out through the wall. At the time of construction it was common for the flashing to be coated with asphalt, and the asphalt coating – not especially attractive in any case – would melt under sunlight and over time it would drip and stain the face of the wall below. More attractive materials are widely used today, including drip edges of proprietary compositions or even stainless steel. The more attractive materials are likely to be more expensive. However, stopping the flashing within the wall may be the most expensive option of all, considering the possible costs of leak remediation.

Posted in Construction Administration, Construction Documents, Design, Masonry, Specifications

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