Q: Our company is designing an office building. The exterior masonry wall extends beyond the intersecting wall to form wing walls and creates an aesthetic feature in the building. A question came up regarding how these wing walls should be flashed.

What should the flashing do at the wing wall when it approaches from the masonry walls on either side of the corner? Should the flashing continue around the wing wall, or should it simply stop with end dams on either side of the wing wall?

A: The answer to this question depends largely on the particulars of the building design. The question ultimately is whether or not water that penetrates the wing wall can enter interior spaces. For instance, in single-story masonry walls supported by a foundation containing a brick ledge where the top of the wing wall foundation is at the level of the lowest portion of the brick ledge, it is unlikely that water will enter the building from flashing leaks. In this case, it may be appropriate to use a fully adhered flashing that follows the vertical face of the brick ledge where the wing wall extends from the building.

In other cases, it may be appropriate to terminate the flashing with an end dam at either side of the wing wall and not continue it through the wing wall itself. In multi-story buildings, the flashing likely needs to be continued around the perimeter of the wing wall in order to prevent water from bypassing the masonry at this corner and entering at lower floors.

Carefully consider where the water from the wing wall will flow when designing flashing details. In many cases, it may be useful to build a model of areas requiring critical flashing details so that the situation can be studied in three dimensions.