Q: We designed a single-wythe masonry wall that has an integral water repellant. Are flashings needed above windows and at the base of the wall in this system?
If so, how can they be installed?
A: Yes, flashings are needed. In fact, flashings may be more important in walls with an integral water repellant than in concrete masonry walls without this additive. The integral water repellent retards moisture from being absorbed by the masonry. Therefore, any water that penetrates through voids or cracks flows through the vertical cells.
The cells of the concrete masonry units actually work like a drainage cavity. Water flowing down the cells of the concrete masonry can result in interior leakage at openings or at the base of the wall if flashing is not provided.
Since this is a single-wythe masonry wall, flashings can be provided by either using half-thickness units at the location of the flashing or by extending the flashing through the thickness of the wall. It is fairly easy to extend the flashing through the wall at the base.
An angle or other device can be attached to the foundation wall to create the back leg of the flashing on the interior. The flashing can be attached to this angle and extend over the top of the foundation wall to the exterior. Dowels in the base of the wall, which are grouted in the concrete masonry, would be sealed at each of the penetrations in the flashing (Fig. 1).
The flashing detail at the head of windows depends on the type of lintel used to support the masonry over the opening. When a steel angle is used as a lintel to support a single wythe of masonry, the flashing is applied on the angle which supports the back leg. The flashing should extend past the end of the lintel and include an end dam within the concrete masonry.
When precast concrete lintels are used in a concrete masonry wall, the flashing should be provided in the course immediately above the precast concrete lintel. The flashing should turn up on the interior (Fig. 2). It is also possible that half-depth units can be used to create a step in the flashing (Fig. 3.)
A consultant at Wiss, Janney, Elstner Associates Inc., Northbrook, Ill.